Echinoderes ahlfeldae, Sørensen & Macheriotou & Braeckman & Smith & Ingels, 2025

Sørensen, Martin V., Macheriotou, Lara, Braeckman, Ulrike, Smith, Craig R. & Ingels, Jeroen, 2025, Antarctic Kinorhyncha: Seven new species from the Antarctic Peninsula, European Journal of Taxonomy 1000 (1), pp. 1-102 : 32-42

Echinoderes ahlfeldae sp. nov

urn:lsid:zoobank.org:act:E59B6DA9-45BD-4DE8-80E6-16529FBEC3A1

Figs 9–12 , Tables 9–10

Diagnosis

Echinoderes with acicular spines in middorsal position on segments 4, 6, and 8, and in lateroventral positions on segments 6 to 9. Tubes present in subdorsal and ventrolateral positions on segment 2, in lateroventral positions on segment 5, in sublateral positions on segment 8, and in laterodorsal positions on segment 10; tubes on segment 10 show sexual dimorphism and are longer in males. Sieve plates on segment 9 in sublateral positions. Males with flare-like extensions from secondary fringe of sternal plates on segment 10. Female papillae or glandular cell outlets type 2 not present. Dorsal glandular cell outlets type 1 are present in middorsal positions on segments 1 to 3, 5, 7, and 10, and in paradorsal positions on segments 4, 6, 8, and 9.

Etymology

The species name is dedicated to Katie Ahlfeld, museum specialist at the USNM, in appreciation of her work maintaining the Smithsonian invertebrate collections and of the numerous kinorhynch loans she has issued to the first author.

Material examined

Holotype ANTARCTICA • ♀ (mounted for LM in Fluoromount G on HS slide); Antarctic Peninsula, CRS 1792; 64°51.40′ S, 62°34.01′ W; 525 m b.s.l.; 11 Apr. 2016; FjordEco2; soft sediment; NHMD 1784759 .

Paratypes

ANTARCTICA – Antarctic Peninsula • 7 ♂♂ (mounted as holotype); CRS 1698; 64°51.60′ S, 62°33.80′ W; 541 m b.s.l.; 28 Nov. 2015; FjordEco1; soft sediment; NHMD 1784762 to 1784766 , USNM 1740029 to 1740030 • 1 ♂ (mounted as holotype); CRS 1769; 64°52.37′ S, 62°25.27′ W; 547 m b.s.l.; 5 Apr. 2016; FjordEco2; soft sediment; NHMD 1784768 • 4 ♂♂, 2 ♀♀ (mounted as holotype); CRS 1790; 64°51.49′ S, 62°34.01′ W; 532 m b.s.l.; 10 Apr. 2016; FjordEco2; soft sediment; NHMD 1784770 to 1784773 , USNM 1740031 to 1740032 • 1 ♂, 2 ♀♀ (mounted as holotype); same data as for holotype; NHMD 1784760 to 1784761 , USNM 1740033 • 1 ♂ (mounted as holotype); CRS 1793 ; 64°39.53′ S, 62°55.03′ W; 701 m b.s.l.; 11 Apr. 2016; FjordEco2; soft sediment; NHMD 1784774 • 6 ♂♂, 5 ♀♀ (mounted as holotype); CRS 1809; 64°39.59′ S, 62°55.09′ W; 694 m b.s.l.; 15 Apr. 2016; FjordEco2; soft sediment; NHMD 1784775 to 1784782 , USNM 1740034 to 1740036 .

Additional material

ANTARCTICA – Antarctic Peninsula • 2 ♂♂, 1 ♀ (mounted for SEM); CRS 1698; 64°51.60′ S, 62°33.80′ W; 541 m b.s.l.; 28 Nov. 2015; FjordEco1; soft sediment; MVS • 1 juv. (mounted as holotype); CRS 1698; 64 o 51.60′ S, 62 o 33.80′ W; 541 m b.s.l.; 28 Nov. 2015; FjordEco1; soft sediment; NHMD 1784767 • 1 ♂ (mounted for SEM); CRS 1773; 64°52.35′ S, 62°25.88′ W; 553 m b.s.l.; 6 Apr. 2016; FjordEco2; soft sediment; MVS • 4 ♂♂, 2 ♀♀ (mounted for SEM); same data as for holotype; MVS • 12 ♂♂, 7 ♀♀ (mounted for SEM); CRS 1793; 64°39.53′ S, 62°55.03′ W; 701 m b.s.l.; 11 Apr. 2016; FjordEco2; soft sediment; MVS • 4 ♂♂, 1 ♀ (mounted for SEM); CRS 1799; 64°51.51′ S, 62°33.83′ W; 541 m b.s.l.; 13 Apr. 2016; FjordEco2; soft sediment; MVS • 11 ♂♂, 6 ♀♀ (mounted for SEM); CRS 1809; 64°39.59′ S, 62°55.09′ W; 694 m b.s.l.; 15 Apr. 2016; FjordEco2; soft sediment; MVS • 1 ♂, 7 ♀♀ (mounted for SEM); CRS 1832; 64°39.30′ S, 62°55.98′ W; 631 m b.s.l.; 21 Apr. 2016; FjordEco2; soft sediment; MVS .

Description

GENERAL. Adults with head, neck and eleven trunk segments ( Figs 9 , 10 , 11A , 12A–B ). An overview of measurements and dimensions is given in Table 9. Distributions of cuticular structures, i.e., sensory spots, glandular cell outlets, spines, and tubes, are summarized in Table 10.

HEAD. Consists of a retractable mouth cone and an introvert ( Figs 10 , 12C–D ). Mouth cone with nine outer oral styles composed of two units; all oral styles with uniform morphology, but differ alternatingly in length, with styles in uneven numbered sectors being ca 15% longer than those in even numbered ( Fig. 12C ). A partly folded structure with seven spikes (lateral ones longest) is present at the base of each outer oral style. A set of double fringes is located more basally, at the base of the mouth cone and in between the attachment points of the outer oral styles. Inner oral styles could not be examined.

INTROVERT. With ten primary spinoscalids in Ring 01 ( Fig. 10 ). Each primary spinoscalid consists of a basal sheath and a distal end piece with a blunt tip ( Fig. 12D ). The sheaths have two transverse fringes; the most proximal fringe has the strongest fringe tips. End-pieces are flexible, with two longitudinal fringes on their proximal parts, whereas they are smooth on their distal halves. Rings 02 and 04 have 10 spinoscalids, and Rings 03 and 05 have 20. All spinoscalids in these rings are well-developed and consist of a basal sheath and a pointed end-piece. Ring 06 has only six spinoscalids, located in sectors 1, 3, 5, 6, 7, and 9; they resemble those in preceding sectors, but the distal end-pieces are much shorter, only slightly longer than their proximal sheaths. Ring 07 has two kinds of scalids: one kind resembles those in Ring 06 and are located as pairs in sectors 3 and 9; the other kind resembles trichoscalids ( Fig. 12D ). They have the same bushy appearance, but are much smaller than the actual trichoscalids. These trichoscalid-like scalids are present as pairs in sectors 1, 2, 4, 8, and 10, and as single, laterally displaced ones in sectors 5 and 7 ( Fig. 10 ). Described sector-wise ( Fig. 10 ), sector 1 has its scalids arranged as two double diamonds, anterior to a pair of trichoscalid-like scalids. Sectors 3 and 9 are similar, and also have their spinoscalids arranged as two double diamonds but anterior to a pair of regular scalids. Sectors 2, 4, 8, and 10 all have spinoscalids arranged as a quincunx, located in between an anterior spinoscalid in Ring 02, a posterior pair of trichoscalid-like scalids, and a trichoscalid plate. Sectors 5 and 7 have spinoscalids forming double diamonds, anterior to an unpaired, lateral trichoscalid-like scalid and a trichoscalid plate. Regular trichoscalids with trichoscalid plates are present in sectors 2, 4, 5, 7, 8, and 10.

NECK. With 16 placids. Midventral placid broadest, 17 µm in width and length, whereas all others are narrower, measuring 10 µm in width at their bases. The trichoscalid plates are well-developed and hat-shaped.

SEGMENT 1. Consists of a complete cuticular ring. Sensory spots are present in subdorsal, laterodorsal, and ventromedial positions; subdorsal and laterodorsal sensory spots are present on the anterior half of the segment, but not immediately at the anterior margin. They are composed of a dense tuft of micropapillae around a central pore and are flanked by four to five, irregularly arranged, strong and bristle-like cuticular hairs; ventromedial sensory spots are more posterior, with same appearance as the dorsal ones, but with only two or three cuticular hairs. Glandular cell outlets type 1 are present in middorsal and ventrolateral positions. Besides the few hairs around the sensory spots, the segment has either no cuticular hairs at all, or only very few rigid and bristle-like hairs on the dorsal side. The posterior segment margin is straight and terminates in a well-developed pectinate fringe with broad fringe tips ( Figs 9A–B , 11B–C , 12E–G ).

SEGMENT 2. Consists of a complete cuticular ring; some specimens mounted for SEM had indications of a weak, superficial tergosternal line ( Fig. 12F ), but this line did not occur consistently in all SEM specimens, and none of the specimens mounted for LM had any indications of plate differentiation. Tubes are located in subdorsal and ventrolateral positions; missing tubes in some specimens were evidently broken off. Sensory spots present in middorsal, laterodorsal, and ventromedial positions. The micropapillary areas around the sensory spots on this, and all following segments, are more oval; the micropapillae along the posterior margins of the areas are slightly longer, and one to three very long, hair-like micropapillae extend from the posterior part of the areas. Glandular cell outlets type 1 are present in middorsal and ventromedial positions. Bracteate cuticular hairs are arranged in three transverse rows from the middorsal to the midlateral positions; hairs in the two anteriormost rows are rather short, whereas those of the third row are considerably longer, reaching the pectinate fringe at the posterior segment margin; the ventral half of the segment is devoid of cuticular hairs. The posterior segment margin is straight along the dorsal and lateral sides, but extends in a small midventral V-shaped flap. Pectinate fringe as on preceding segment ( Figs 9A–B , 11B–C , 12E–G ).

SEGMENT 3. As remaining segments, consisting of one tergal and two sternal plates. Sensory spots are present in subdorsal and sublateral positions, and glandular cell outlets type 1 in middorsal and ventromedial positions. The hair covering of the tergal and lateral halves of sternal plates is dense on the anterior half of the segment, except in hair-less midlateral areas; bracteate cuticular hairs are arranged in six to seven rows, with hairs getting gradually longer in the more posterior rows; the hairs in the most posterior row are considerably longer than the others. Paraventral areas without bracteate hairs, but with fine, short hair-like extensions. Posterior segment margin straight and pectinate fringe as on preceding segment ( Figs 9A–B , 11B–C , 12E ).

SEGMENT 4. With spine in middorsal position. Sensory spots are not present. Glandular cell outlets type 1 are present in paradorsal and ventromedial positions. Cuticular hairs as on preceding segment, but in addition to the hairless midlateral areas, the mid- and paradorsal areas are also devoid of hairs. Posterior segment margin and pectinate fringe as on preceding segment ( Figs 9A–B , 11B–C , 12E ).

SEGMENT 5. With tubes in lateroventral positions. Sensory spots present in subdorsal, sublateral and ventromedial positions, and glandular cell outlets type 1 in middorsal and ventromedial positions. Cuticular hairs, posterior segment margin, and pectinate fringe as on preceding segment ( Figs 9A–B , 11B–C , 12E ).

SEGMENT 6. With spines in middorsal and lateroventral positions. Sensory spots present in paradorsal, subdorsal, sublateral, and ventromedial positions. Glandular cell outlets type 1 present in paradorsal and ventromedial positions. Cuticular hairs, posterior segment margin, and pectinate fringe as on preceding segment ( Figs 9A–B , 11B–C ).

SEGMENT 7. With spines in lateroventral positions. Sensory spots present in paradorsal, sublateral, and ventromedial positions. Glandular cell outlets type 1 present in middorsal and ventromedial positions. Cuticular hairs, posterior segment margin, and pectinate fringe as on preceding segment ( Figs 9A–B , 11B–E , 12I–J ).

SEGMENT 8. With spines in middorsal and lateroventral positions, and tubes in sublateral positions. Sensory spots present in paradorsal positions only. Glandular cell outlets type 1 present in paradorsal and ventromedial positions. Cuticular hairs, posterior segment margin, and pectinate fringe as on preceding segment ( Figs 9A–B , 11D–E, G , 12H–J ).

SEGMENT 9. With spines in lateroventral positions. Sensory spots present in paradorsal (posterior on segment), subdorsal (anterior on segment), laterodorsal (medial on segment), and ventrolateral (medial on segment) positions. Glandular cell outlets type 1 present in paradorsal and ventromedial positions. Small rounded sieve plates located in sublateral positions; gaps between sieve plates and lateroventral spines are distinct. The cuticular hair covering is similar to that on preceding segments, but hairless middorsal area is broader, and the hairless lateral areas are in laterodorsal, rather than midlateral positions. Posterior segment margin and pectinate fringe as on preceding segment ( Figs 9A–B , 11D–E, G–H , 12H ).

SEGMENT 10. With sexually dimorphic laterodorsal tubes located near, but not at, the posterior segment margin; female tubes are extremely small, hardly projecting from attachment site; male tubes of more regular size, reaching beyond the segment margin. An additional sexually dimorphic trait is expressed in the secondary fringe, enwrapping the anterior part of the segment; at most other segments the secondary fringe is covered by the free flap of the preceding segment, but in male specimens, a tuft of long setae expands from the secondary fringe on each sternal plate and reaches more than halfway down the exposed part of the segment ( Figs 9D , 11F, H–I , 12K ). In some specimens, the setal extensions appear rather disorganised, but in others they are very well-arranged and spread out from a common shaft, forming a fan- or flare-like structure. Due to this appearance, the structures will be referred to as ‘flare-like extensions from secondary fringe’. No indication of a similar structure is evident in females. Sensory spots present in subdorsal and ventrolateral positions. Glandular cell outlets type 1 present as two longitudinally arranged outlets in middorsal position and in ventromedial positions. Cuticular hairs of uniform length, covering the tergal plate, except in two hairless subdorsal areas; cuticular hairs on sternal plates as on preceding segments. The posterior segment margin of the tergal plate is straight, with very minute fringe tips; the margins of the sternal plates are concave, reaching the posterior margin of the terminal segment, also with very short fringe tips ( Figs 9A–D , 11D–F, H–K , 12K–N ).

SEGMENT 11. With lateral terminal spines. Females with lateral terminal accessory spines; males with thin, tubular dorsal and ventral penile spines, and a well-developed, cone-shaped medial pair of penile spines. Sensory spots present in ventromedial positions, near margins of sternal extensions. A single glandular cell outlet type 1 present in middorsal position. A minute middorsal protuberance-like structure extends from the intersegmentary joint in some specimens ( Fig. 12M ), whereas it is evidently absent in others ( Fig. 12N ); holotype without middorsal protuberance. The segment is devoid of cuticular hairs, but with very short cuticular hair-like structures covering the mid- and paradorsal areas, and the inferior margins of the tergal extensions. Tergal extensions are short and triangular with slightly offset tips. Sternal extensions short, broadly rounded, and not extending beyond tergal extensions ( Figs 9A–D , 11I–K , 12L–N ).

Distribution

Antarctic Peninsula: Gerlache Strait and Andvord Bay MBA, IBB and OBA, 525 to 701 m b.s.l. See Fig. 1 for geographic overview of stations and Table 1 for station and specimen information.

Diagnostic remarks

The composition of segments 1 and 2 forming closed cuticular rings easily assigns the new species to Echinoderes . This generic assignment could, if genus diagnoses of Echinoderidae are used in the strictest possible way, be challenged by the presence of superficial markings on segment 2, which could indicate the presence of partial tergosternal junctions. However, several previous descriptions have demonstrated that a weak indication of a partially developed midventral fissure on segment 2 does not bring the generic assignments to Echinoderes into question ( Sørensen et al. 2012; Herranz et al. 2018; Yamasaki & Dal Zotto 2019; Grzelak et al. 2023). In the case of E. ahlfeldae sp. nov. the superficial fissures on segment 2 are lateroventral rather than midventral, which to our knowledge has not been observed previously among species of Echinoderidae , but since the indications are only superficial lines on the cuticle, never observable with LM, and not even occurring in all specimens, we would not put any taxonomic value into this trait. Instead, it only confirms that the ring-like composition of segment 2 might show a certain level of variation within Echinoderes .

Among species of Echinoderes , E. ahlfeldae sp. nov. shares the common pattern with middorsal spines on segments 4, 6, and 8, and lateroventral tubes or spines on segments 5 to 9, with no less than 27 congeners ( Yamasaki et al. 2020b). However, if this tube-spine pattern is combined with the presence of sublateral tubes on segment 8 and the complete lack of glandular cell outlets type 2, the list of similar candidates is shortened dramatically to only three species, i.e., E. hispanicus Pardos et al., 1998 , E. leduci Grzelak & Sørensen, 2022 , and E. newcaledoniensis Higgins, 1967 . These three species certainly show great resemblance to each other and to E. ahlfeldae , but still they can be distinguished from the latter by carrying additional pairs of tubes in various positions. Likewise, E. newcaledoniensis has laterodorsal and sublateral tubes on segment 2, whereas subdorsal tubes are lacking, and it has in addition midlateral tubes on segment 9 and lateral accessory tubes on segments 6 to 8 ( Higgins 1967). Also E. hispanicus differs, by having sublateral tubes on segment 2 and lateral accessory tubes or spines on segment 8 ( Pardos et al. 1998). The species showing the closest resemblance to E. ahlfeldae is E. leduci . However, E. leduci differs by its uncommon lack of regular cuticular hairs that have been replaced by minute scales, by having laterodorsal tubes on segment 9, and by having its dorsal tubes on segment 2 in laterodorsal rather than subdorsal positions ( Grzelak & Sørensen 2022). Even without taking the lack of glandular cell outlets type 2 into account, the combined spine and tube pattern in E. ahlfeldae is unique within the genus, which makes identification of the species fairly easy.

The distribution of glandular cell outlets type 1 in E. ahlfeldae sp. nov. follows the MD Seg. 1–3, 5, 7, PD 4, 6, 8–9 pattern (see table with summary of species with this pattern described up to 2020 in Sørensen et al. 2020). Among species described after 2020, this pattern is also found in E. leduci , which stresses the close resemblance between the two species.

Two other noteworthy characters in E. ahlfeldae sp. nov. are the position of the sieve plates and the uncommon flare-like extensions from the secondary fringes of the sternal extensions of segment 10 in males. The sieve plates in species of Echinoderes are most commonly located in lateral accessory positions on segment 9, but a slight relocation to sublateral positions is not uncommon either. Therefore, the sieve plate positions rarely play an important role as a diagnostic character. However, during the species identification phase of the present study, their positions turned out to be an extremely handy character when distinguishing between E. ahlfeldae and E. nataliae sp. nov. (see description below). The two species have a rather similar appearance, especially when it comes to specimens mounted for SEM, with only the ventral and parts of the lateral sides exposed. However, in E. nataliae the sieve plates sit in lateral accessory positions, very close to the lateroventral spines, and soon during the identification phase the position of the sieve plates became the easy way to distinguish between the two species when other diagnostic characters were hidden. This example shows that even the most unexpected character trait can suddenly become useful in species recognition.

Another subtle, but yet significant trait of E. ahlfeldae sp. nov. is the flare-like extensions from the secondary fringes of the sternal plates on segment 10 in male specimens. When first observed, the flare-like structures were considered to be unique for the species, because something like this was certainly never reported previously. The most similar, and also the only, published example of a structure like this are the tufts of long hairs reported from Echinoderes pterus Yamasaki et al., 2018a . However, the structures in E. pterus differ in several points: they are much stronger and appear more like a brush; they are present on the tergal plate and on segment 9; and they are present in both sexes. Thus, the similarities between the hairy tufts in E. pterus and the flare-like extensions in E. ahlfeldae are only superficial, and the structures in the latter species were therefore initially considered to be limited to this particular species. However, as discussed above, the similarities between E. ahlfeldae and E. leduci led to a closer examination of unpublished SEM images of the latter species and, surprisingly, similar structures were found in this species. In E. leduci they also appear on the sternal plates of segment 10 and were found in two males mounted for SEM (their presence in females could not be confirmed though, as the only available female mounted for SEM was mounted on its ventral side). Their appearance and position in E. leduci clearly suggest that the structures are homologous with the flare-like extensions in E. ahlfeldae , but they also showed clear differences. Whereas the flares in E. ahlfeldae consist of six to eight setal threads, only one to three threads were present in E. leduci . This obviously makes the structure much more indistinct, which also explains why they were not mentioned in the original description ( Grzelak & Sørensen 2022). In addition to the occurrence in these two species, similar setal threads was found in one of the new species, E. nataliae sp. nov. (see following description). In this species, the setal threads are also restricted to males and are formed as extensions from the secondary fringe of the sternal plates of segment 10. However, in E. nataliae only a single thread is present on each sternal plate, in contrast to the more numerous threads found in E. ahlfeldae .

Figures

Fig. 9. Line art illustrations of Echinoderes ahlfeldae sp. nov. A. Female, dorsal view. B. Female, ventral view. C. Male, segments 10 to 11, dorsal view. D. Male, segments 10 to 11, ventral view.

Fig. 10. Diagram of mouth cone (grey area), introvert, and placids in Echinoderes ahlfeldae sp. nov., showing distribution of inner oral styles (closed dots,) outer oral styles, scalids, and trichoscalids. Table shows the scalid arrangement by sector (S1 to S10); single-lined boxes mark quincunxes, double-lined boxes mark “double diamonds”.

Fig. 11. Light micrographs showing overviews and details of Echinoderes ahlfeldae sp. nov. A–E, J–K. Female, holotype (NHMD 1784759). F. Male, paratype (NHMD 1784764). G. Female, paratype (NHMD 1784760). H. Male paratype (NHMD 1784768). I. Male paratype (NHMD 1784775). A. Ventral overview. B. Segments 1 to 6, dorsal view. C. Segments 1 to 6, ventral view. D. Segments 7 to 10, dorsal view. E. Segments 6 to 10, ventral view. F. Segment 10, ventral view, showing male sexual dimorphism. G. Segments 8 to 9, ventral view. H. Segments 9 to 10, ventral view, showing male sexual dimorphism. I. Segments 10 to 11, ventral view, showing male sexual dimorphism. J. Segments 10 to 11, focused on tergal extensions, showing female sexual dimorphism. K. Segments 10 to 11, ventral view, showing female sexual dimorphism. Scale bars: A = 100 µm; B–E = 25 µm; F–K = 20 µm.

Fig. 12. Scanning electron micrographs showing overviews and details of Echinoderes ahlfeldae sp. nov. A. Dorsal overview of female. B. Ventrolateral overview of male. C. Mouth cone, ventral view. D. Introvert focused on the midventral sector 1 and sector 10. E. Segments 1 to 5, dorsal view. F. Segments 1 to 2, ventral view. G. Segments 1 to 2, right lateral view. H. Segments 8 to 9, right lateral view. I. Segments 7 to 8, ventral view. J. Segments 7 to 8, right lateral view. K. Detail of sternal plates of segment 10 with male dimorphic flare-like extensions from the secondary fringe. L. Segments 10 to 11, ventral view, showing male sexual dimorphism. M. Segments 10 to 11, right lateral view, showing male sexual dimorphism. N. Segments 10 to 11, dorsal view, showing female sexual dimorphism. Scale bars: A–B = 100 µm; C–G, I–J, L–M = 20 µm; H, N = 10 µm; K = 5 µm.

Fig. 1. Map showing the sampling stations. A. Overview of Antarctica, with the Antarctic Peninsula framed. Previous records of Polacanthoderes martinezi Sørensen, 2008 (green dots) and P. shiraseae Yamasaki et al., 2022 (red dots) are marked. B. Antarctic Peninsula with sampling area framed. C. Sampling area with station numbers and stations indicated as yellow dots. Study sites in Andvord Bay refer to OBA – Outer Basin A; MBA – Middle Basin A; IBB – Inner Basin B. Only stations yielding adult kinorhynch specimens are included.