taxonID	type	description	language	source
1B0B87EFFFACFFDEC730409CBF491774.taxon	description	urn: lsid: zoobank. org: act: 55 EFA 3 A 3 - D 7 E 8 - 4 DAB-BC 8 A- 1 A 6 FC 39 EF 051	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFACFFDEC730409CBF491774.taxon	type_taxon	Type species Cirrinerilla sulcipalpata gen. et sp. nov.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFACFFDEC730409CBF491774.taxon	diagnosis	Diagnosis Cirrinerilla gen. nov. is morphologically diagnosed by the following unique combination of characters: body cigar-shaped with eight segments. Prostomium with three, long and straight antennae and two long, cylindrical palps. Trunk segments with very long parapodial cirri. Compound chaetae in all segments. Hermaphroditic, with one pair of spermioducts opening in segment VII and one pair of oviducts in segment VIII.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFACFFDEC730409CBF491774.taxon	etymology	Etymology The genus name relates to the presence of long parapodial ‘ cirri’ and ‘ nerilla’ refers to the type genus of Nerillidae. The Japanese name for this new genus is given here as ‘ Iejima-usamimi-gokai-zoku’ (meaning ‘ Ie Island-rabbit ear-bristle worm’ in English).	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFACFFC5C76E4515BD17140A.taxon	description	urn: lsid: zoobank. org: act: 1 C 802929 - 4 F 05 - 48 D 8 - B 205 - 38957594 C 97 D Figs 3 – 4; Table 3	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFACFFC5C76E4515BD17140A.taxon	diagnosis	Diagnosis Cirrinerilla gen. nov. with very long antennae, up to ⅔ of body length. Palps ventrally densely ciliated and dorsally with longitudinal non-ciliated furrow. Eyes absent. Long cylindrical parapodial cirri of minimum half body length in segments II – VII, longest in segment V. Maximum 12 compound chaetae per parapodium. Dorsal and ventral transverse rows of ciliary tufts on each segment.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFACFFC5C76E4515BD17140A.taxon	etymology	Etymology ‘ Sulcipalpata’ refers to the dorsal, longitudinal furrow on each palp. The Japanese name for this new species is given here as ‘ Iejima-doukutsu-usamimi-gokai’ (meaning ‘ Ie Island-cave dwelling-rabbit ear-bristle worm’ in English).	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFACFFC5C76E4515BD17140A.taxon	materials_examined	Type material Holotype JAPAN • adult; Okinawa Prefecture, Ie Island, ‘ Unnamed Cave’ (or sometimes called ‘ Sho-doukutsu’); 26.72518 ° N, 127.83107 ° E; 5 – 12 meters depth; 9 Jun. 2019; Y. Fujita, M. J. Hansen, M. C. Allentoft-Larsen and K. Worsaae leg.; NHMD 1842011 mounted on SEM stub. Paratypes JAPAN • 4 adults; same data as for holotype; 5 – 17 meters depth; 2 – 9 Jun. 2019; NHMD 1842012 and 1842013 as permanent whole mounts, NMHD 1842014 and 1842015 mounted on SEM stub • 1 spec. examined with LM but lost during preparation for SEM; same data as for preceding. Representative DNA sequences GenBank accession numbers PQ 149834 – PQ 149835 (nuclear 18 S rRNA), PQ 149816 – PQ 149817 (nuclear 28 S rRNA), PQ 570584 – PQ 570585 (nuclear H 3) and PQ 421126 – PQ 421127 (mitochondrial COI); from specimen with same collection data as holotype (Table 1).	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFACFFC5C76E4515BD17140A.taxon	description	Description Measurements are based on LM of holotype, counts and ciliation from SEM of holotype; values for paratype are given in parentheses. Body about 525 µm long (500 – 685 µm, n = 5) with eight segments (Figs 3 A, 4 A). Segment I double length of following segment (n = 6); segment lengths of holotype 98, 53, 72, 70, 63, 53, 43, 28 µm, pygidium 24 µm long. Cigar-shaped body. Segment V widest, segments VII – VIII decreasing in length and width (n = 6). Maximum width of trunk segments, including parapodia, about 125 µm (115 – 180 µm, n = 3); about 90 µm excluding parapodia (90 – 125 µm, n = 3). Max length of parapodium segment I, 37 µm (35 – 45, n = 5); max length in segments II – VIII, 34 µm (37 – 48 µm, n = 5). Prostomium carrying three antennae and two straight palps (Fig. 3 A, C, E). Palps 117 µm long (121 µm, n = 2) and 18 µm in width (23 µm, n = 1) with heavy ventral ciliation and dorsal longitudinal furrow. Lateral antennae cylindrical with a length of about 400 µm, estimated relative to LM measure of total body length from dissection scope images of live holotype (la, Fig. 3 E). Scars from lateral and median antennae visible in fixed holotype (las, mas, Figs 3 C, 4 D). Characteristics of median antenna unknown. Eyes absent. Elongated esophageal glands in segments II – IV, along foregut (Fig. 3 A). Parapodial cirri observed on live specimens on segments II – V and VII (cirri assumed lost in segment VI, absent on segment I (buccal segment) and VIII); increasing in length posteriorly until segment V. Cirri of segment V noticeably longest; maximum length of 310 µm estimated relative to LM measure of total body length from dissection scope images of live holotype (pc, Fig. 3 E). Parapodial cirri lost in fixed specimens. Pygidial cirri lost in all specimens; only regenerating bud of cirrus recorded (rpc, Fig. 3 A). Compound chaetae in all segments. Up to ten chaetae in one bundle on each parapodium of segment I, pointing posteriorly, maximum 149 µm long (141 µm, n = 1). Segments II – VIII with up to 12 chaetae per parapodium (five-seven in each dorsal and ventral bundle, respectively; often broken or lost). Chaetae maximum 127 µm long (84 – 138 µm, n = 5) (cc, Fig. 4 B, G); shaft up to 96 µm long (52 – 111 µm, n = 5), blade up to 31 µm long (20 – 63 µm, n = 5), distal extension on shaft at joint 2 µm long (n = 1). Prostomium with anterior and posterior fields of presumed sensory cilia and lateral rows of cilia extending from insertion of lateral antenna and more than halfway towards insertion of nearest palp (lrc, Fig. 4 D). Paired, densely ciliated nuchal organs on dorsolateral border between prostomium and segment I. Palps ventrally with longitudinal dense ciliary row from insertion point to tip of palps (pvc, Fig. 4 D), lined by ventrolateral row of ciliary tufts (each tuft with up to six cilia). Palps lost in most specimens during SEM and CLSM preparation. Segment I with paired dorsolateral transverse rows of each three ciliary tufts (each tuft with minimum four cilia) at the level of parapodia. Trunk segments each with dorsal transverse row of up to 20 ciliary tufts (with middorsal gap in segments III – V) on slightly elevated dorsal ridges at level of parapodia (tdc, Fig. 4 B – C). Ventral ciliation consisting of i) densely ciliated mouth, ii) midventral ciliary band and iii) continuous transverse rows of cilia in all segments at level of parapodia (vc, tvc, Fig. 4 A, F). Multiple single cilia scattered on dorsal, lateral, and ventral sides of body. Three to ten blind ending enteronephridia extend from transition between mid- and hindgut, posteriorly along hindgut (ent, Fig. 3 D). Four pairs of segmental nephridia run laterally in segments III – VI, originating more dorsally and opening ventrolaterally (n 3 – n 6, Fig. 3 G). Hermaphroditic. One pair of spermioducts opening in segment VII, and one pair of oviducts opening in segment VIII, both with an anterior ciliated ‘ funnel’ and separate ventral openings (Figs 3 H, 4 E). Mature egg and many oocytes observed in a single specimen in segments IV – VI (Fig. 3 B).	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFACFFC5C76E4515BD17140A.taxon	distribution	Distribution and habitat ‘ Unnamed Cave (or ‘ Sho-doukutsu’) ’, northeastern reef of Ie Island, Okinawa Prefecture, Ryukyu Islands, Japan. Marine anchialine cave with entrance from the reef slope at 17 meters depth and main tube penetrating about 50 meters under land (see Osawa & Fujita 2019 for the description of the cave). Specimens collected at 5 – 17 meters depth from plankton tow and sediment samples from the main tube and the anchialine right hall of the cave. Associated nerillids from the cave include Leptonerilla sp. 3, Mesonerilla gamaglandulata sp. nov. and Trochonerilla sp. 1.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFACFFC5C76E4515BD17140A.taxon	description	Molecular information Cirrinerilla sulcipalpata gen. et sp. nov. is nested within a fully supported larger clade comprising the seven- to eight-segmented genera Trochonerilla, Micronerilla, and Aristonerilla (Fig. 2). Within this clade, Cirrinerilla gen. nov. is sister group to Aristonerilla (PP / BS: 1 / 92), together with Micronerilla constituting a fully supported subclade, sister to Trochonerilla. The phylogenetic analyses (Fig. 2) include two terminals of C. sulcipalpata found to represent identical haplotypes. Pairwise comparison of C. sulcipalpata gen. et sp. nov. sequence similarity to phylogenetic closely related species: 18 S rRNA – 100 % intraspecific similarity between the two C. sulcipalpata sequences – 89.28 – 93.59 % similar to its sister group (Aristonerilla brevis (Saphonov & Tzetlin, 1997) and A. sp. 1); 28 S rRNA – 100 % intraspecific similarity – 66.21 – 66.38 % similar to its sister group; COI – 100 % intraspecific similarity – 74.67 – 80.44 % similar to its sister group; H 3 – 100 % intraspecific similarity – 96.65 % similar to its sister group.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFACFFC5C76E4515BD17140A.taxon	discussion	Remarks (see also Table 3 for genus comparisons) Cirrinerilla sulcipalpata gen. et sp. nov. shows closest morphological and molecular similarity to species of Aristonerilla and Micronerilla, and to a lesser degree to species of Trochonerilla. Species of all four genera have less than nine segments, three antennae, relatively long parapodial cirri, and are of similar small size. However, Cirrinerilla sulcipalpata differs from all species of these closely related genera by being hermaphroditic, having a cigar-shaped body narrowing in width anteriorly and posteriorly, and by having significantly longer and straighter palps with a dorsal longitudinal furrow. Moreover, it differs from species of Trochonerilla by having compound rather than capillary chaetae and by lacking dense transverse segmental ciliary bands. It also differs from species of Aristonerilla by having eight rather than seven segments and from species of Micronerilla by having only single rather than double parapodial cirri on each parapodium as well as only a single rather than two pairs of spermioducts. Therefore, we choose to erect the new genus Cirrinerilla gen. nov., since a designation of the new species to Aristonerilla, Micronerilla or Trochonerilla would otherwise result in a considerable ambiguity of their diagnostic genus characters (e. g., reproductive mode, segment number, chaetal type), generally assumed to be constant within the genera of Nerillidae (Jouin 1971; Tzetlin & Larionov 1988; Worsaae 2021; Worsaae et al. 2021 a). Additionally, Cirrinerilla sulcipalpata gen. et sp. nov. differs from the closely related species of Aristonerilla and Micronerilla by having longer and straight (rather than wrinkled) antennae, lacking eyes, and having relatively longer parapodial cirri, especially on segment V. Noticeably, A. brevis is reported to sometimes possess comparatively much longer parapodial cirri on segment VII (Müller 2002).	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB6FFC3C7224077B8D611F6.taxon	description	urn: lsid: zoobank. org: act: CAD 96362 - 1 FDA- 4243 - 813 E- 4 F 2 FBE 68 AA 5 E Figs 5 – 6; Table 4	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB6FFC3C7224077B8D611F6.taxon	diagnosis	Diagnosis A nine-segmented Leptonerilla diagnosed by a combination of following characteristics: three long antennae all distally wrinkled, median antenna shorter than lateral antennae. Segment I with cirriform, relatively short cirri and chaetae. Trunk segments with long, double parapodial cirri and long pygidial cirri, exceeding half of body length. Gonochoristic with one pair of oviducts in segment VIII, males not observed.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB6FFC3C7224077B8D611F6.taxon	etymology	Etymology The species is named in recognition of the annelid researcher Günter Purschke, who erected the genus Leptonerilla and described the morphologically highly similar L. diplocirrata Westheide & Purschke, 1996. The Japanese name for this new species is given here as ‘ Shimoji-doukutsu-usamimi-gokai’ (meaning ‘ Shimoji Island-cave dwelling-rabbit ear-bristle worm’ in English).	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB6FFC3C7224077B8D611F6.taxon	materials_examined	Type material Holotype JAPAN • ♀ adult; Miyako Islands, Shimoji Island, ‘ Akuma-no-yakata’ (Devil’s Hole); 24.82291 ° N, 125.13551 ° E; rubble at 22 meters depth; 26 Oct. 2018; Y. Fujita, M. Mizuyama, P. R. Møller and K. Worsaae leg.; NHMD 1842016 mounted on SEM stub. Paratype JAPAN • 1 ♀ adult; same data as for holotype; NHMD 1842017 as permanent whole mount. Representative DNA sequences GenBank accession numbers PQ 149839 (nuclear 18 S rRNA), PQ 149820 (nuclear 28 S rRNA), PQ 570589 (nuclear H 3) and PQ 421135 (mitochondrial COI); from specimen with same collection data as holotype (Table 1).	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB6FFC3C7224077B8D611F6.taxon	description	Description Measurements are based on LM of holotype, counts and ciliation from SEM; values for paratype are given in parentheses. Body with nine chaetigerous segments (Fig. 5 A), total length about 940 µm (745 µm, n = 1). Segment lengths of holotype 97, 90, 104, 123, 115, 103, 101, 77, 68 µm, pygidium 37 µm long. Maximum width about 195 µm including parapodia (165 µm, n = 1), about 145 µm excluding parapodia (115 µm, n = 1). Max length of parapodium on segment I, 41 µm (38, n = 1), on segments II – IX, 45 µm (53 µm, n = 1). Prostomium with three long antennae wrinkled distally (Fig. 5 C), often lost during fixation. Lateral antenna estimated length up to 485 µm (n = 1) (la, Fig. 5 A, C), median antenna shorter than lateral antennae (ma, Fig. 5 C) with estimated length up to 370 µm from photos of live specimen (n = 1). Prostomium with two club-shaped palps up to 78 µm long (65 µm, n = 1) and 31 µm wide (20 µm, n = 1), inserted ventrally on prostomium (pa, Figs 5 A, C, 6 A – B) with distinct ventral and frontal ciliation. Two dorsal eyes. Paired nuchal organs laterally between prostomium and peristomium (no, Fig. 6 B). Segment I with a single, up to 73 µm long, cylindrical (cirriform) cirrus per parapodium (Figs 5 A, 6 B). Segments II – IX carrying double, cylindrical interramal parapodial cirri (pc, Figs 5 B, 6 A), up to 336 µm long, lengths seemingly increasing in posterior segments. Cylindrical pygidial cirri up to 590 µm long (pyc, Fig. 5 C), estimated relative to body length from live specimen images. Compound chaetae in all segments (cc, Fig. 5 B). Segment I with one bundle of up to 18 posteriorly pointing chaetae (up to 148 µm long) per parapodium (Fig. 6 A – B). Following segments with dorsal and ventral bundles of chaetae; up to 20 chaetae per parapodia (up to 236 µm long) (Fig. 6 A). Shaft up to 169 µm long, blade up to 82 µm long, distal extension on shaft at joint up to 15 µm long (Fig. 6 C – D). Prostomium with anterior and posterior fields of presumed sensory cilia and lateral rows of cilia extending between lateral antenna and palp insertion (Fig. 6 B). Paired, densely ciliated nuchal organs on lateral border between prostomium and segment I. Palps with ventral longitudinal dense ciliary row from insertion point to tip of palps, dorsal row of minimum 4 ciliary tufts on distal half of palp (each tuft with> 15 cilia), and lateral row of indistinct small tufts of cilia (Fig. 6 B). Segment I with paired dorsolateral transverse rows of each two ciliary tufts (each tuft with> 20 cilia) at the level of parapodia. Following trunk segments with dorsal transverse continuous row of up to 14 ciliary tufts at level of parapodia (tdc, Fig. 6 A – B); tufts increasing in numbers, ciliary length and showing remarkable density in posterior segments. Segment II with an additional lateral pair of longitudinal ciliary bandlets (ldc, Fig. 6 B). Ventral ciliation could not be observed. Four pairs of segmental nephridia positioned laterally, parallel to ventral nerve cord, opening in segments IV, V, VI and VII (n 4 – n 7, Fig. 5 E). Enteronephridia not distinguished. Gonochoristic reproduction; females with one pair of straight oviducts opening latero-ventrally just anterior to the segmental nerve in segment VIII (ov, Fig. 5 D). Spermioducts unknown. A single mature egg (about 80 µm long) observed in segments VI – VII (n = 2).	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB6FFC3C7224077B8D611F6.taxon	distribution	Distribution and habitat Devil’s Hole ‘ Akuma-no-yakata’, northwestern coast of Shimoji Island, Ryukyu Islands, Miyako Islands, Japan. Anchialine cave located on coral reef slope. Specimen collected from rubble patches in middle zone of cave at about 22 meters depth (see Osawa & Fujita 2019 for the description of the cave). Associated nerillids from the cave include Mesonerilla sp. (Worsaae, unpubl. record and not sequenced), N. irabuensis and Leptonerilla sp. 2.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB6FFC3C7224077B8D611F6.taxon	description	Molecular information Leptonerilla purschkei sp. nov. constitutes a fully supported clade with L. westheidei sp. nov. and Leptonerilla sp. 1 (Fig. 2). The clade is sister to a larger clade comprising the remaining Leptonerilla spp. Pairwise comparison of L. purschkei sp. nov. sequence similarity to other Leptonerilla spp.: 18 S rRNA – 99.43 – 99.89 % similar to its sister group (clade comprising L. westheidei sp. nov and L. sp. 1) – 97.13 – 98.24 % similar to the remaining Leptonerilla spp.; 28 S rRNA – 96.16 % similar to its sister group – 79.30 – 82.72 % similar to the remaining Leptonerilla spp.; COI – 88.62 – 89.57 % similar to its sister group – 79.12 – 80.40 % similar to the remaining Leptonerilla spp.; H 3 – 96.59 % similar to its sister group – 88.09 – 89.31 % similar to the remaining Leptonerilla spp.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB6FFC3C7224077B8D611F6.taxon	discussion	Remarks (see also Table 4 for Leptonerilla spp. comparisons) Leptonerilla purschkei sp. nov. shows the greatest morphological and molecular similarity to L. westheidei sp. nov., but differs from it by a larger body size, segment I with much shorter cirri, and double as many chaetae. Both species share a small body size compared to L. diatomeophaga (Núñez in Núñez, Ocaña & Brito, 1997) and especially L. prospera Sterrer & Iliffe, 1982 (Sterrer & Iliffe 1982; Núñez et al. 1997; Worsaae et al. 2009). Leptonerilla purschkei differs from these latter two species by having longer cirriform, cylindrical parapodial cirri on segment I, although these are similar in shape and relative length to those of L. diplocirrata. Leptonerilla purschkei differs from all other species of Leptonerilla by the very long pygidial cirri and by the very long antennae, more than half the body length, with a wrinkled appearance, otherwise only described for the distantly related Micronerilla and Aristonerilla (Swedmark 1959; Saphonov & Tzetlin 1997; Müller 2002). It thereby also differs from the only other described species of Leptonerilla from the West pacific region, L. diplocirrata found more than 1000 kilometres away, near Hainan, China. Leptonerilla purschkei also differs molecularly from both L. sp. 2 found within the same cave and L. sp. 3 found further North off Okinawa in ‘ unnamed cave’ of Ie Island. Both two latter potential new cave species were only found as single specimens with very limited morphological information obtainable prior to DNA extraction of all their tissue.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB1FFCCC71E4397BE59121C.taxon	description	urn: lsid: zoobank. org: act: 756 B 9 FFA- 2 D 1 E- 49 B 3 - AF 75 - 7558 EF 2 FA 291 Fig. 7; Table 4	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB1FFCCC71E4397BE59121C.taxon	diagnosis	Diagnosis A Leptonerilla diagnosed by a combination of following characteristics: three antennae, two club-shaped palps. Segment I with relatively long, unpaired, cylindrical cirri and few chaetae. Following trunk segments with long, double parapodial cirri. Gonochoristic; females with one pair of oviducts in segment VIII, males not observed.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB1FFCCC71E4397BE59121C.taxon	etymology	Etymology The species is named in recognition of the annelid researcher Wilfried Westheide, who erected the genus Leptonerilla and described the morphologically highly similar L. diplocirrata.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB1FFCCC71E4397BE59121C.taxon	materials_examined	Type material Holotype SOUTH KOREA • adult; Jeju Island, Munseom Islet; 33.22772 ° N, 126.56330 ° E; sand and shell gravel around 25 meters depth; 21 Oct. 2015; K. Worsaae and T. Park leg.; NIBRIV 0000927415 mounted on SEM stub. Paratype SOUTH KOREA • 1 adult; same data as for holotype; NIBRIV 0000927416 mounted on SEM stub. Representative DNA sequences GenBank accession numbers PQ 149836 (nuclear 18 S rRNA), PQ 570586 (nuclear H 3) and PQ 421134 (mitochondrial COI); from specimen collected near type locality: SOUTH KOREA • Jeju Island, Beomseom Islet; 33.22115 ° N, 126.51809 ° E; sand and shell gravel at around 20 meters depth; 23 Oct. 2015 (Table 1).	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB1FFCCC71E4397BE59121C.taxon	description	Description Measurements are based on LM of holotype, counts and ciliation from SEM; values for paratype are given in parentheses. Body with nine chaetigerous segments (Fig. 7 A – B), total length about 705 µm (565 – 640 µm, n = 2). Segment lengths 54, 75, 91, 83, 81, 78, 74, 65, 63 µm. Maximum width about 180 µm including parapodia (140 – 145 µm, n = 2), about 130 µm excluding parapodia (90 – 95 µm, n = 2). Prostomium with median and two lateral antennae (only scars visible) and two, ventrally inserted, short, club-shaped palps (47 – 50 µm long and 35 – 36 µm wide, n = 2) (las, mas, pa, Fig. 7 A, D, F). Presence of eyes difficult to discern in fixed material. Parapodium of segment I uniramous with long, single, cylindrical (cirriform) cirrus, up to 120 µm long (85 µm, n = 1) and inserted ventral to the chaetal bundle (bc, Fig. 7 B, D, F). All trunk segments with long, cylindrical, double, interramal cirri (Fig. 7 A), up to 263 µm long (186 – 192 µm, n = 2). Parapodial cirri with few evenly scattered cilia. Pygidium with scars from two lost cirri and midterminal short, cirriform lobe (pyl, Fig. 7 A). Compound chaetae in segments I – IX plus 1 – 2 short, dorsal, bent, simple chaetae in most trunk segments (n = 2). Up to nine posteriorly pointing compound chaetae in segment I (n = 3), maximum 135 µm long (Fig. 7 A, D, F); up to 18 compound chaetae in segments II – IX (n = 3), maximum 195 µm long (blade up to 150 µm, shaft up to 54 µm, extension of shaft at chaetal joint up to 8 µm) (Fig. 7 A); length of chaetae increasing posteriorly. Prostomium with anterior and posterior fields of presumed sensory cilia, lateral rows of cilia between lateral antenna and palp insertion, paired densely ciliated nuchal organs on lateral border between prostomium and segment I (Fig. 7 D, F). Palps with ventral longitudinal dense ciliary row from insertion point to tip of palps (pvc, Fig. 7 F), dorsal row of minimum 3 ciliary tufts on distal half of palp (each tuft with> 15 cilia) (ct, Fig. 7 F), and lateral row of small tufts of cilia (sct, Fig. 7 F). Segment I with paired dorsolateral transverse rows of each two ciliary tufts at the level of parapodia. Following trunk segments with dorsal transverse continuous row of up to 12 ciliary tufts at level of parapodia (tdc, Fig. 7 A, C, E); tufts increasing in numbers, ciliary length, and density in posterior segments. Segment II with an additional lateral pair of longitudinal ciliary bandlets (ldc, Fig. 7 E). Ventral ciliation not examined. Gonochoristic. Females with mature eggs (up to 110 µm long) and oocytes in segments VI – VIII (eg, Fig. 6 B). Nephridia and gonoducts not examined.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB1FFCCC71E4397BE59121C.taxon	distribution	Distribution and habitat Western coast of Munseom Islet and northern coast of Beomseom Islet, south of Jeju Island, South Korea. Collected between 20 – 25 meters depth from sediment consisting of sand and shell gravel. Associated nerillids from the Munseom and Beomseom islets include Meganerilla sp. 2, Mesonerilla dannyi sp. nov. and Nerillidium sp. 1.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB1FFCCC71E4397BE59121C.taxon	description	Molecular information Leptonerilla westheidei sp. nov. always groups together with L. purschkei sp. nov. and L. sp. 1 in all phylogenetic analyses. Pairwise comparison of L. westheidei sp. nov. sequence similarity to other Leptonerilla spp.: 18 S rRNA – 99.66 % similar to its sister group (L. sp. 1) – 97.25 – 99.89 % similar to the remaining Leptonerilla spp.; COI – 96.53 % similar to its sister group (L. sp. 1) – 81.29 – 89.57 % similar to the remaining Leptonerilla spp.; H 3 – 98.66 % similar to its sister group – 89.69 – 96.59 % similar to the remaining Leptonerilla spp.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB1FFCCC71E4397BE59121C.taxon	discussion	Remarks (see also Table 4 for Leptonerilla spp. comparisons). The small sized Leptonerilla westheidei sp. nov. shows the greatest morphological and molecular similarity to the two geographically closest species L. purschkei sp. nov. from Japan and L. diplocirrata from Hainan, China. It differs, however, from both by its half number of chaetae in segment I, and from these and all other species of Leptonerilla by having much longer cirri on segment I and molecular differences (see also remarks of L. purschkei). Specimens of L. westheidei sp. nov. used for morphological examination were collected from Munseom Islet, while the specimen used for DNA analysis was obtained from Beomseom Islet and identified in the field prior to DNA extraction.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFBEFFC9C73B40EFBD8B1427.taxon	description	urn: lsid: zoobank. org: act: 4 A 0 AF 43 F-DC 06 - 4522 - BA 89 - CDBD 236 CE 3 EF Figs 8 – 9; Table 5	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFBEFFC9C73B40EFBD8B1427.taxon	diagnosis	Diagnosis Meganerilla without a median antenna. Small body length, less than 450 µm. No eyes present. Short cirri in segment I. Parapodial cirri increasing in length posteriorly; glandular pigmentation in parapodial cirri of segments VI – VII and distally in pygidial cirri. Chaetae only lacking in segment I.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFBEFFC9C73B40EFBD8B1427.taxon	etymology	Etymology Named after the type locality at ‘ Ie Island’, and the Latin root ‘ - ensis ’ (‘ of’). The Japanese name for this new species is given here as ‘ Sango-usamimi-gokai’ (meaning ‘ Coral reef-rabbit ear-bristle worm’ in English).	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFBEFFC9C73B40EFBD8B1427.taxon	materials_examined	Type material Holotype JAPAN • late juvenile; Ryukyu Islands, Okinawa Prefecture, Ie Island; 26.72518 ° N, 127.83107 ° E; coarse coral sand at 13 – 15 meters depth; 3 Jun. 2019; Y. Fujita, M. J. Hansen, M. C. Allentoft-Larsen and K. Worsaae leg.; NHMD 1842018 mounted on SEM stub. Representative DNA sequences GenBank accession numbers PQ 149840 (nuclear 18 S rRNA), PQ 149821 (nuclear 28 S rRNA), PQ 570590 (nuclear H 3) and PQ 421132 (mitochondrial COI); from specimen with same collection data as holotype (Table 1).	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFBEFFC9C73B40EFBD8B1427.taxon	description	Description Measurements are based on LM of holotype, counts and ciliation from SEM (no measurements from SEM pictures where the specimen seemingly shrank to about 60 % of live length). Body about 405 µm long with nine segments (Figs 8 A, 9 C). Segment lengths of 43, 44, 40, 47, 47, 45, 54, 31, 27 µm. Trunk segments about 90 µm wide including parapodia, about 55 µm excluding parapodia. Segments II – VII similar in length and width, segments VIII and IX shorter and less wide, possibly because not fully grown (Figs 8 A – B, 9 B). Prostomium round with straight palps, increasing slightly in width distally (pa, Figs 8 C, 9 A). Palp 92 µm long and 29 µm wide. Prostomial lateral ciliary band next to palp insertion. Antennae and indicative scars thereof absent. Eyes absent. Nuchal organs laterally in groove between prostomium and segment I (no, Figs 8 C, 9 A, E). Cirri on segment I short, 13 µm long and with several cilia on and / or next to cirri (Fig. 9 F). Lanceolate parapodial cirri on segments III – VIII, increasing in length and width posteriorly until segment VII (pc, Figs 8 B, D, 9 B – C), maximum length 38 µm. Parapodial cirri on segments VI – VII with brown pigmented glands (Fig. 8 D). Short pygidium with cylindrical pygidial cirrus, 73 µm long, and a shorter regenerating cirrus, 41 µm long (pyc, Figs 8 A – B, 9 B – C). Pygidial cirri with brown pigmentation at distal tip. Capillary chaetae in all trunk segments, increasing in length posteriorly until segment VIII, maximum 72 µm long. Maximum six chaetae in each parapodium of segments II – IX; many chaetae lost. Prostomium with anterior and posterior fields of presumed sensory cilia and lateral rows of cilia next to palp insertion. Paired, densely ciliated nuchal organs on lateral border between prostomium and segment I (acf, lrc, pcf, Fig. 9 A, C, E – F). Palp with ventral longitudinal dense ciliary row from insertion to tip of palp, and lateral rows of small tufts of cilia (ct, sct, pcf, Fig 9 F). Segment I with paired dorsolateral transverse rows of ciliary tufts at level of parapodia. Following trunk segments with dorsal transverse continuous rows of cilia in all segments at level of parapodia (tdc, Fig. 9 A – B). Ventral ciliation consisting of i) densely ciliated mouth (mo, Fig. 9 C, E), ii) midventral longitudinal ciliary band extending from mouth to pygidium and iii) transverse ventral rows of cilia of up to 6 ciliary tufts in all segments at level of parapodia (tvc, vc, Fig. 9 C). Multiple single cilia scattered on dorsal, lateral, and ventral sides of body. Reproduction unknown. Nephridia and gonoducts not investigated.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFBEFFC9C73B40EFBD8B1427.taxon	distribution	Distribution and habitat Reef slope in front of and near Unnamed Cave, northern part of eastern reef of Ie Island, Okinawa Prefecture, Ryukyu Islands, Japan. Patches of coarse coral sand with shells and small coral fragments at 13 – 15 meters of depth between corals. Associated nerillids from the same locality include Nerillidium sp. 2 and Mesonerilla sp. 4.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFBEFFC9C73B40EFBD8B1427.taxon	description	Molecular information Meganerilla iensis sp. nov. nests within a fully supported clade of Meganerilla spp., next to Meganerilla sp. 1 from Miyako Islands, Japan (with no morphological information available). Pairwise comparison of Meganerilla iensis sp. nov. sequence similarity to other Meganerilla spp.: 18 S rRNA – 99.77 % similar to its sister taxon (M. sp. 1) – 97.89 – 99.54 % similar to the remaining Meganerilla spp.; 28 S rRNA – 99.80 % similar to M. sp. 1 – 88.35 – 97.83 % similar to the remaining Meganerilla spp.; COI – 94.56 % similar to M. sp. 1 – 94.07 % similar to the remaining Meganerilla spp.; H 3 – 100 % similarity M. sp. 1 – 90.52 – 96.27 % similar to the remaining Meganerilla spp.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFBEFFC9C73B40EFBD8B1427.taxon	discussion	Remarks (see also Table 5 for Meganerilla spp. comparisons) Like its five congeneric described relatives, M. iensis sp. nov. has nine segments, simple chaetae, lanceolate or leaf-shaped parapodial cirri (not found in Meganerilla bactericola (Müller, Bernhard & Jouin-Toulmond, 2001 )) and relatively large palps (Boaden 1961; Magagnini 1966; Riser 1988; Müller et al. 2001; Westheide 2008; Worsaae et al. 2009; Worsaae 2021). Meganerilla iensis sp. nov. is smaller in size compared to other species of Meganerilla (Boaden 1961; Núñez et al. 1997; Worsaae et al. 2009); however, the holotype may not be fully grown. Meganerilla iensis does not possess any median antenna, as in M. cesari and M. bactericola, and lacks chaetae in the first segment but not in the following trunk segment. Moreover, M. iensis possesses apomorphic pigmented glands in the parapodial and pygidial cirri. Meganerilla sp. 1 and M. iensis sp. nov. were collected from two Japanese islands about 350 km apart. Neither species was found in isolated caves, as Meganerilla sp. 1 was collected from subtidal sand at Irabu Island. The two taxa show a high molecular affinity (99.77 % for 18 S rRNA; 99.80 % for 28 S rRNA; 98.56 % for COI; 100 % for H 3), but no morphological information is available for Meganerilla sp. 1. Out of caution, they are so far treated as separate species mainly due to dissimilarities in COI. Additional morphological and molecular data are necessary to assess the taxonomic status of Meganerilla sp. 1.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB9FFF1C7784077B8711797.taxon	description	urn: lsid: zoobank. org: act: E 06 FA 3 A 6 - 4975 - 48 AB- 977 B- 232 B 72 E 7 CE 8 C Figs 10 – 11; Table 6	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB9FFF1C7784077B8711797.taxon	diagnosis	Diagnosis Mesonerilla with similar-sized cylindrical parapodial cirri on segments II – I, and longer cylindrical pygidial cirri. Three antennae, median short and slightly swollen. Segment I with chaetae and short cirri. Three pairs of pigmented glands in segments I and II. Ventral transverse rows of ciliary tufts between parapodia and intersegmentally. About 14 enteronephridia spanning the hindgut; pairs of nephridia opening in segments III, IV, V. Hermaphroditic with spermioducts opening in segments VI and VII and gonoducts in segment VIII.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB9FFF1C7784077B8711797.taxon	etymology	Etymology ‘ Gama’, means ‘ cave’ in Okinawan dialect and ‘ glandulata’ refers to the relatively many glands associated with palps, peristomium and oesophagus. The Japanese name for this new species is given here as ‘ Gama-usamimi-gokai’ (meaning ‘ Cave dwelling-rabbit ear-bristle worm’ in English).	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB9FFF1C7784077B8711797.taxon	materials_examined	Type material Holotype JAPAN • adult; Okinawa Prefecture, Ie Island, ‘ Unnamed Cave’ (or ‘ Sho-doukutsu’); 26.72518 ° N, 127.83107 ° E; 5 – 12 meters depth; 9 Jun. 2019; Y. Fujita, M. J. Hansen, M. C. Allentoft-Larsen and K. Worsaae leg.; NHMD 1842019 mounted on SEM stub. Paratypes JAPAN • 3 adults; same data as for holotype; 3 Jun. 2019; NHMD 1842021 to NHMD 1842023 (mounted on SEM stubs) • 1 adult; same data as for holotype; 10 – 17 meters depth; 3 Jun. 2019; NHMD 1842020 as permanent whole mount. Representative DNA sequences GenBank accession numbers PQ 149843 (nuclear 18 S rRNA), PQ 149824 (nuclear 28 S rRNA), PQ 570593 (nuclear H 3) and PQ 421136 (mitochondrial COI); from specimen with same collection data as holotype (Table 1).	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB9FFF1C7784077B8711797.taxon	description	Description Measurements are based on LM of holotype, counts and ciliation from SEM, and values for paratypes are given in parentheses. Hyaline body, about 785 µm long (670 – 785 µm, n = 4) with nine segments (Figs 10 A, 11 A). Segment lengths of holotype 93, 91, 92, 94, 101, 83, 78, 67, 60 µm. Trunk segments about maximum 135 µm wide, including parapodia (135 – 150 µm, n = 3), about 105 µm excluding parapodia (100 – 110 µm, n = 3). Prostomium with club-shaped palps, 81 µm long (64 – 82 µm, n = 3) and 41 µm wide (36 – 40, n = 3) (pa, Figs 10 A, D, 11 B, F – G) with unique lateral row of 4 – 6 glandular papillae interspersed by tufts of cilia (ppl, Fig. 11 C). Median antenna cylindrical and slightly swollen distally (ma, Figs 10 C, 11 B, F), 84 µm long (75 – 80 µm, n = 3). Only scars from lateral antennae left but presence further documented by CLSM of lateral antennae muscles in prostomium (lam, mam, Fig. 10 E). Eyes absent. Paired nuchal organ between prostomium and segment I. Three groups of dark, paired glands: i) small, dorso-anterior on segment I and extending ventrally, ii) large, rounded, opening into mouth cavity, and iii) large group, dorsally in segment II (oesophageal?) (gl, Fig. 10 D). Parapodial cirri in segment I short (bc, Figs 10 D, 11 A – B), 15 – 20 µm long (16 – 22 µm, n = 3). Trunk segments with cylindrical cirri of similar length (pc, Figs 10 A – B, 11 A), maximum 55 µm (49 – 59 µm, n = 3). Pygidium with 216 µm long cylindrical cirrus (pyc, Fig. 10 A). Straight to slightly curved compound chaetae in all segments. Parapodia with up to eight chaetae, maximum 75 µm long in segment I and maximum 120 µm long in trunk segments. Prostomium with anterior and posterior fields of sensory cilia extending between lateral antennae scars and palp insertions (acf, pcf, Fig. 11 B, G). Paired densely ciliated nuchal organs on dorsolateral border between prostomium and segment I. Palps with ventral longitudinal dense ciliary row from insertion points to tip of palps, lined by dorsolateral row of five ciliary tufts present posteriorly (each tuft with up to 15 cilia). Segment I with paired dorsolateral transverse rows of each two ciliary tufts (each tuft with> 10 cilia) at the level of parapodia. Continuous transverse dorsolateral row with numerous cilia on all trunk segments, extending from basis of parapodia to about halfway to mid-dorsal line (tdc, Fig. 11 A – B). Ventral ciliation consisting of i) densely ciliated mouth (mo, Fig. 11 G), ii) midventral longitudinal ciliary band extending from mouth to pygidium (vc, Fig. 11 E) and iii) transverse rows of up to five tufts of cilia on each parapodia (tvc, Fig. 11 D, H). Additional ventral row intersegmentally with 2 – 6 tufts between segments I – VIII. Three pairs of discontinuous ciliated nephridia extending along segments and opening latero-ventrally in segments III, IV, V (n 3 – n 5, Fig. 10 F). About 14 enteronephridia extending along the hindgut (en, Fig. 10 H – I), on the dorsal (4), lateral (6) and ventral (4) sides. Hermaphroditic with two pairs of slightly curved dorsoventrally extending spermioducts opening separately in segments VI and VII (sp, Figs 10 G, 11 E, H) and one pair of relatively straight oviducts opening in segment VIII (ov, Figs 10 G, 11 H).	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB9FFF1C7784077B8711797.taxon	distribution	Distribution and habitat Unnamed Cave ‘ Sho-doukutsu’, eastern reef of Ie Island, Okinawa Prefecture, Ryukyu Islands, Japan. Submarine cave located on the reef slope. Specimens collected from plankton tow and sediment samples from the anchialine right hall of the cave, at 5 – 17 meters of depth; see Osawa & Fujita (2019) for the description of the cave. Associated nerillids from the cave include Cirrinerilla sulcipalpata gen. et sp. nov., Leptonerilla sp. 3 and Trochonerilla sp. 1.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB9FFF1C7784077B8711797.taxon	description	Molecular information Mesonerilla gamaglandulata sp. nov. is found in both analyses (Fig. 2) as a sister taxon to M. armoricana Swedmark, 1954 and M. roscovita Levi, 1953, albeit with low support (PP / BS: 0.51 / 69). Together, this clade has a sister relationship to M. dannyi sp. nov. (PP / BS: 1 / 99). The hermaphroditic Mesonerilla spp. within clade C does not form a monophyletic sub-clade, as Nipponerilla irabuensis groups with the previously mentioned species of Mesonerilla, although with low support (PP / BS: 0.68 / 79), and this clade is itself sister to the hermaphroditic Mesonerilla fagei Swedmark, 1959 (PP / BS: 1 / 96). Morphologically, M. gamaglandulata sp. nov. has a strong resemblance to the three hermaphroditic Mesonerilla spp. and exhibits a high degree of similarity in 18 S rRNA and 28 S rRNA sequences. Pairwise comparison of M. gamaglandulata sp. nov. sequence similarity to other hermaphroditic Mesonerilla spp. and Nipponerilla irabuensis: 18 S rRNA – 98.83 – 98.89 % similar to its sister group (clade comprising M. armoricana and M. roscovita) – 98.88 – 99.14 % similar to remaining hermaphroditic Mesonerilla spp. – 96.92 % similar to N. irabuensis; 28 S rRNA – 90.52 % similar to its sister group – 89.42 – 91.37 % similar to the remaining hermaphroditic Mesonerilla spp. – 84.89 % similar to N. irabuensis; COI – 72.86 % similar to the remaining hermaphroditic Mesonerilla spp. – 70.36 % similar to N. irabuensis; H 3 – 90.76 – 92.32 % similar to its sister group – 86.72 % similar to the remaining hermaphroditic Mesonerilla spp. – 91.97 % similar to N. irabuensis.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFFB9FFF1C7784077B8711797.taxon	discussion	Remarks (see also Table 6 for comparisons of morphologically similar nerillids) With its nine segments, compound chaetae, spoon-shaped palps, three antennae, equally long parapodial cirri and configuration of gonoducts M. gamaglandulata sp. nov. bears most resemblance to the three hermaphroditic species of Mesonerilla (M. roscovita, M. fagei and M. armoricana) and Mesonerilla dannyi sp. nov. (Levi 1953; Swedmark 1959; Westheide 2008; Worsaae et al. 2019 a, 2021 a; Worsaae 2021). Mesonerilla gamaglandulata shares different characteristics with the three hermaphroditic Mesonerilla including the presence of chaetae and shorter cirri in segment I (also seen in M. fagei), ventrolateral rows of cilia, oesophageal glands and cylindrical pygidial cirri (also seen in M. roscovita and M. fagei) and a swollen median antenna and spoon-shaped palps (also seen in M. armoricana) (Levi 1953; Swedmark 1959; Westheide 2008; Worsaae et al. 2019 a). The main difference between M. gamaglandulata and Mesonerilla dannyi is the presence or absence of chaetae in segment I, respectively. Mesonerilla gamaglandulata, Mesonerilla dannyi and N. irabuensis were monophyletic in the Bayesian and maximum likelihood analyses and they all have compound chaetae, nine segments and three antennae. Nipponerilla irabuensis differs from the two others by having a cigar-shaped body, spermioducts in segments VII and VIII and being gonochoristic. In contrast to M. gamaglandulata, N. irabuensis also has long palps and a relatively long median antenna (Worsaae et al. 2021 b), traits that could not be determined from Mesonerilla dannyi. Apart from M. gamaglandulata sp. nov., oesophageal glands have also been recorded in M. laerkae, Mesonerilla katharinae Worsaae, Mikkelsen & Martínez, 2019, M. roscovita, M. fagei and M. xurxoi Worsaae, Mikkelsen & Martínez, 2019, with two lateral glands also being observed in segment I of the latter species (Worsaae et al. 2019 a). Furthermore, M. minuta Jouin, 1970 has about 10 yellowish dorsal epidermal glands on each side of segment I (Swedmark 1959). Three independent groups of glands in the head region, as seen in M. gamaglandulata, have, to our knowledge, not been recorded previously in Nerillidae and the anteriormost pair of small glands seems unique to the species.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFF83FFF2C71F4435BF8615D3.taxon	description	urn: lsid: zoobank. org: act: 32 DE 4 DE 5 - C 0 FB- 4 AE 8 - BAE 5 - D 108 C 2 E 8114 C Fig. 12; Table 6	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFF83FFF2C71F4435BF8615D3.taxon	diagnosis	Diagnosis Mesonerilla with three antennae. Segment I uniramous, with oval cirri; trunk segments biramous with cylindrical parapodial cirri. Pygidial cirri cylindrical. Row of seven dorsolateral ciliary tufts on palps. Trunk segments with short continuous ventrolateral band of cilia at each parapodia. Paired dorsolateral rows of cilia at basis of parapodia, not medially connecting. Dorsolateral ciliary tufts next to chaetae in segments II – VII. Gonochoristic. Females with rounded brooding hood extruding from the dorsal epidermis of segment VIII.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFF83FFF2C71F4435BF8615D3.taxon	etymology	Etymology The species name refers to the characteristic stone statues and deities (Dol-Hareubang, which means ‘ Stone Grandfather’) of Jeju Island in South Korea, a large island geographically close to the islets where the species was collected.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFF83FFF2C71F4435BF8615D3.taxon	materials_examined	Type material Holotype SOUTH KOREA • ♀; Jeju Island, Munseom Islet; 33.22772 ° N, 126.56330 ° E; sand and shell gravel at around 28 meters depth; 21 Oct. 2015; K. Worsaae and T. Park leg.; NIBRIV 0000924478 mounted on SEM stub. Paratypes SOUTH KOREA • 4 ♀♀ adults; same data as for holotype; NIBRIV 0000924479 to NIBRIV 0000924482 mounted on SEM stub • 3 adults; same data as for holotype; NIBRIV 0000924483 to NIBRIV 0000924485 mounted on SEM stub. Representative DNA sequences GenBank accession numbers PQ 149844 (nuclear 18 S rRNA) and PQ 570594 (nuclear H 3); from specimen collected near type locality: SOUTH KOREA • Jeju Island, Seopseom Islet; 33.2294 ° N, 126.6027 ° E; shell gravel at around 33 meters depth, 19 October 2015, same collectors as holotype (Table 1).	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFF83FFF2C71F4435BF8615D3.taxon	description	Description Measurements are based on holotype and values for paratypes are given in parentheses, all measurements obtained from SEM. Body with nine chaetigerous segments (Fig. 12 A), total length about 590 µm excluding appendages (455 – 725 µm, n = 7). Trunk segments similar in size and up to about 130 µm wide including parapodia (120 – 125 µm, n = 2), about 80 µm excluding parapodia (75 – 80 µm, n = 2). Prostomium with club-shaped palps, 56 µm long (50 – 52 µm, n = 2) and 23 µm wide (26 – 28 µm, n = 2) (pa, Fig. 12 A, C – D), and three antennae (las, mas, Fig. 12 B – D). Lateral antennae lost in holotype and in all but one paratype (148 µm long) (la, Fig. 12 B). Median antenna, 30 µm and possibly broken (ma, Fig. 12 B). Eyes absent. Paired nuchal organs dorsolaterally between prostomium and segment I (no, Fig. 12 B). Parapodia uniramous in segment I (Fig. 12 B, D), with short oval cirrus in paratype (36 µm long) (bc, Fig. 12 D). Parapodia biramous in segments II – IX, with cylindrical and tapering interramal cirrus (pc, Fig. 12 A, F); increasing in length posteriorly up to 123 µm (56 – 152 µm, n = 7). Pygidium with 70 µm long cirri similar in shape to parapodial cirri, (pyc, Fig. 12 H). Compound chaetae in all segments. Chaetae with distal extension (es, Fig. 12 G) and increasing in length towards pygidium. Parapodia with up to 10 chaetae in segment I, maximum 109 µm long (42 – 98 µm, n = 7). Up to 13 neuro- and 13 notochaetae in segments II – IX, maximum 184 µm long (127 – 191 µm, n = 7). Prostomium with anterior and posterior fields of cilia and paired lateral ciliary bands extending between lateral antenna and palps insertion (an, Fig. 12 D). Palps ciliated continuously on frontal side from insertion point to tip of palps (ct, Fig. 12 C), lined by dorsolateral row of ciliary tufts present posteriorly (each tuft with up to seven cilia). Ventral ciliation consisting of i) densely ciliated mouth (mo, Fig. 12 D), ii) midventral longitudinal ciliary band extending from mouth to pygidium (vb, Fig. 12 F) and iii) short transverse ventrolateral band of at least 20 cilia on each parapodia (vt, Fig. 12 F – G). Continuous transverse dorsolateral row with numerous cilia on all trunk segments, extending from basis of parapodia to about halfway to mid-dorsal line (dt 1, Fig. 12 E). Dense dorsolateral tuft of more than 20 cilia on each parapodium next to notochaetae insertion and cirrus in segments II – VII (dt 2, Fig. 12 E). Dorsal ciliation patterns of last two segments not observable. Few individual cilia scattered on ventral and dorsal surfaces. Sixteen ciliary tufts observed on ridge of the brooding hood (ct, Fig. 12 H). Gonochoristic. Females with round brooding hood, 103 µm long and 126 µm wide, in segment VII at parapodia level (bh, Fig. 12 A, H), partially covering up to two embryos attached dorsally. One embryo typically more developed. Juveniles attached to female with six chaetigers maximum and conspicuous parapodia. Male gonopores not found. Nephridia and gonoducts not studied.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFF83FFF2C71F4435BF8615D3.taxon	distribution	Distribution and habitat Eastern coast of Seopseom Islet and the western coast of Munseom Islet, south of Jeju Island, South Korea. Collected from 22 – 33 meters depth from sediment consisting of sand and shell gravel. Associated nerillids from the Seopseom and Munseom Islets include Leptonerilla westheidei sp. nov., Mesonerilla dannyi sp. nov. and Nerillidium sp. 1.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFF83FFF2C71F4435BF8615D3.taxon	description	Molecular information Only the maximum likelihood analysis resolved M. harubangi sp. nov. as a sister group to Mesonerilla sp. 2 and M. laerkae (albeit poorly supported, BS: 78) within the large clade of gonochoristic Mesonerilla spp. Pairwise comparison of M. harubangi sp. nov. sequence similarity to other gonochoristic Mesonerilla spp.: 18 S rRNA – 96.28 – 97.42 % similar to its sister group (clade comprising M. laerkae and M. sp. 2) – 96.22 – 97.38 % similar to the remaining gonochoristic Mesonerilla spp.; COI – 65.28 – 65.86 % similar to its sister group – 56.57 – 71.65 % similar to the remaining gonochoristic Mesonerilla spp.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFF83FFF2C71F4435BF8615D3.taxon	discussion	Remarks (see also Table 6 for comparisons of morphologically similar nerillids) Mesonerilla harubangi sp. nov. has nine segments, compound chaetae and club-shaped palps, and thereby conforms to the main characteristics of Mesonerilla. Furthermore, it resembles M. intermedia and M. laerkae by possessing a brooding hood and being gonochoristic (Worsaae 2005 a, 2021; Worsaae et al. 2019 a). Mesonerilla laerkae has a pointed tip on the brooding hood and equally long parapodial cirri in the trunk segments, which is not seen in either M. harubangi or M. intermedia. Mesonerilla harubangi differs from both species by being smaller in size and by not possessing continuous dorsolateral transverse ciliary rows (found in M. intermedia). The dorsal and ventral ciliation patterns of M. harubangi are most comparable to those of M. xurxoi, but this species does not possess a brooding hood (Worsaae et al. 2019 a). Specimens of M. harubangi sp. nov. used for morphological examination were collected from Munseom Islet, while the specimen used for DNA analysis was obtained from Seopseom Islet and identified in the field prior to DNA extraction. The unresolved phylogenetic position of M. harubangi sp. nov. among the other gonochoristic Mesonerilla could be explained by the absence of two of the four genes, as only 18 S rRNA and COI fragments were successfully obtained. Individual maximum likelihood analysis of COI sequences found M. harubangi as sister group to Mesonerilla, Meganerilla, Speleonerilla, N. irabuensis, C. sulcipalpata gen. et sp. nov., Micronerilla, Leptonerilla, Trochonerilla and Aristonerilla. This is also reflected in the low pairwise sequence similarity of COI between M. harubangi and all other gonochoristic Mesonerilla (around 60 %). Inclusion of additional sequence data is expected to clarify the phylogenetic position of this species within the clade of gonochoristic Mesonerilla spp.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFF80FFFEC73147F1B8461062.taxon	description	urn: lsid: zoobank. org: act: AF 47235 F- 7 D 0 A- 464 E- 904 C- 61 D 83 C 1 E 2 AA 3 Figs 13 – 14; Table 6	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFF80FFFEC73147F1B8461062.taxon	diagnosis	Diagnosis Hermaphroditic Mesonerilla with three antennae and equally short parapodial cirri on segments II – VIII. Segment I with short, ovoid cirri and lacking chaetae. Hermaphroditic with two pairs of spermioducts with separate openings in segments VI, VII, and one pair of oviducts opening in segment VIII.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFF80FFFEC73147F1B8461062.taxon	etymology	Etymology Named in honour of Danny Eibye-Jacobsen, in recognition of his valuable contributions to annelid taxonomy and systematics, as well as his highly appreciated mentorship of the first author.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFF80FFFEC73147F1B8461062.taxon	materials_examined	Type material Holotype SOUTH KOREA • adult; Jeju Island, Munseom Islet; 33.22779 ° N, 126.5675 ° E; shell gravel with mud at 25 meters depth; 24 May 2018; K. Worsaae and T. Park leg.; NIBRIV 0000924486 as permanent whole mount. Paratypes SOUTH KOREA • 2 adults; Jeju Island, Seopseom Islet; 33.2304 ° N, 126.6015 ° E; shell gravel at 15 meters depth; 25 May 2018; K. Worsaae and T. Park leg.; NHMD 1842024, NHMD 1842025 mounted on SEM stubs. Representative DNA sequences GenBank accession numbers PQ 149847 (nuclear 18 S rRNA), PQ 149827 (nuclear 28 S rRNA) and PQ 570598 (nuclear H 3); from specimen with same collection data as holotype (Table 1).	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFF80FFFEC73147F1B8461062.taxon	description	Description Measurements are based on LM of holotype, counts and ciliation from SEM; values for paratypes are given in parentheses. Body with nine segments (Figs 13 A, 14 A), total length about 875 µm long (810 – 985 µm, n = 3). Trunk segments up to about 185 µm wide including parapodia (155 – 185 µm, n = 3), about 120 µm (115 – 135 µm, n = 3) excluding parapodia. Segment lengths of paratype 72, 69, 86, 102, 92, 112, 88, 77, 49 µm. Round prostomium with palps and antennae lost in all mounted specimens, but median antennal and lateral antennal scars observed in SEM (las, ma, Fig. 13 A – B). Eyes absent. Nuchal organs visible with CLSM and SEM (no, Fig. 14 B). Parapodial cirri in segments I – IX. Segment I with short cylindrical cirri, 35 µm long (33 µm long, n = 1) (bc, Fig. 13 B). Segments II – VIII with cylindrical, slightly tapering cirri, up to 65 µm long (54 – 74 µm long, n = 3), similar in length, slightly shorter cirri on segment VIII (pc, Fig. 13 C). Only regenerating pygidial cirri were observed (rpc, Fig. 13 D). Compound chaetae in segments II – IX, with up to 12 chaetae per parapodium and maximum 180 µm long (128 – 155 µm long, n = 2) (cc, Fig. 14 A). Prostomium with anterior and posterior fields of presumed sensory cilia (acf, Fig. 14 B). Paired, densely ciliated nuchal organs on dorsolateral border between prostomium and segment I (no, Fig. 14 B). Ventral ciliation consisting of i) densely ciliated mouth (mo, Fig. 14 C), ii) midventral longitudinal ciliary band extending from mouth to pygidium (vc, Fig. 14 C – D) and iii) transverse rows of up to about 10 small ciliary tufts at level of parapodia (tvc, Fig. 14 D). Multiple single cilia scattered on dorsal, lateral, and ventral sides of body. Many cilia lost during preparation. Three lateral enteronephridia extending from posterior end of stomach along the hindgut until pygidium (Fig. 13 F). Spermioducts present in segments VI and VII with posterior ventral opening. Two relatively long and slender oviducts opening ventrally in segment VIII (so, ovo, Figs 13 E, 14 D).	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFF80FFFEC73147F1B8461062.taxon	distribution	Distribution and habitat Eastern coast of Seopseom Islet and southern coast of Munseom Islet, south of Jeju Island, South Korea. Collected from 25 meters depth from shell gravel with mud. Associated nerillids from Munseom Islet include Leptonerilla westheidei sp. nov., M. harubangi sp. nov. and Nerillidium sp. 1.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFF80FFFEC73147F1B8461062.taxon	description	Molecular information Mesonerilla dannyi sp. nov. is found as sister group to a clade composed of M. gamaglandulata sp. nov., Mesonerilla roscovita and Mesonerilla armoricana (PP / BS: 1 / 99). Mesonerilla dannyi sp. nov., like M. gamaglandulata sp. nov., has a high sequence similarity of 18 S rRNA and 28 S rRNA to three hermaphroditic Mesonerilla. Pairwise comparison of M. dannyi sp. nov. sequence similarity to other hermaphroditic Mesonerilla and Nipponerilla irabuensis: 18 S rRNA – 98.88 – 99.04 % similar to its sister group (clade comprising M. gamaglandulata sp. nov., M. roscovita and M. armoricana) – 99.11 % similar to M. fagei – 97.52 % similar to N. irabuensis; 28 S rRNA – 89.42 % similar to its sister group – 90.85 % similar to M. fagei – 84.86 % similar to N. irabuensis; COI – 72.86 % similar to its sister group – 68.07 % similar to N. irabuensis.	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
1B0B87EFFF80FFFEC73147F1B8461062.taxon	discussion	Remarks (see also Table 6 for comparisons of morphologically similar nerillids) Mesonerilla dannyi sp. nov. is morphologically most similar to the hermaphroditic Mesonerilla (Levi 1953; Swedmark 1959; Worsaae et al. 2019 a), due to its nine-segmented body, compound chaetae, three antennae, equally short and single parapodial cirri in segments II – VIII, and its configuration of gonoducts. It shares the absence of chaetae in segment I with M. roscovita and M. armoricana as well as the presence of short, ovoid cirri with M. fagei. Similar to M. armoricana, M. fagei and M. gamaglandulata sp. nov., cirri on the last segment are similar or nearly equal in length to cirri in the remaining trunk segments (Levi 1953; Swedmark 1959; Worsaae et al. 2019 a).	en	Worsaae, Katrine, Hansen, Malte J., Defourneaux, Éloïse, Olesen, Jørgen, Park, Jiseon, Park, Taeseo, Fujita, Yoshihisa (2025): High diversity and new species of meiofaunal Nerillidae (Annelida) in subtidal sediments and anchialine caves of the East China Sea. European Journal of Taxonomy 1021: 1-54, DOI: 10.5852/ejt.2025.1021.3075, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/3075/13717
