Desmoscolex (Desmoscolex) nibelungus, García-Cobo & González-Casarrubios & Sánchez, 2025

García-Cobo, Marta, González-Casarrubios, Alberto & Sánchez, Nuria, 2025, Description of two new species of Desmoscolex Claparède, 1863 (Nematoda: Desmoscolecidae) from the Cassidaigne Canyon, Mediterranean Sea, European Journal of Taxonomy 1004, pp. 211-236 : 219-226

publication ID	https://doi.org/10.5852/ejt.2025.1004.2969
publication LSID	lsid:zoobank.org:pub:B054F879-D806-4DA9-BAFC-512B263CB101
DOI	https://doi.org/10.5281/zenodo.16422960
persistent identifier	https://treatment.plazi.org/id/E8363960-FFB1-8A4D-7BEF-4E50F0EC94E2
treatment provided by	Plazi
scientific name	Desmoscolex (Desmoscolex) nibelungus
status	sp. nov.

Treatment

Desmoscolex (Desmoscolex) nibelungus sp. nov.

urn:lsid:zoobank.org:act:159D1F58-029D-40A1-8760-4E1376076352

Figs 1–4 View Fig View Fig View Fig View Fig , Tables 1–3 View Table 1 View Table 2 View Table 3 , 6 View Table 6

Diagnosis

Desmoscolex (Desmoscolex) nibelungus sp. nov. is mainly defined by: (1) presence of 17 main rings with typical desmoscolecid setae arrangement: nine pairs of subdorsal setae and eight pairs of subventral setae; (2) thick somatic setae, except for wiry terminal pair (3) slightly elongated subdorsal setae on the 16 th ring and more elongated subdorsal setae on the 17 th ring; (4) apparent absence of cephalic setae; (5) rounded cephalic region, with lip region not covered by concretion material; (6) strongly ventrally curved, beak-shape last main ring.

Etymology

The specific name ‘ nibelungus ’ refers to the cycle of four epic music dramas composed by Richard Wagner called The Ring of the Nibelung (‘Der Ring des Nibelungen’ in German). Name chosen due to the presence of rings on the nematode’s body.

Type material

Holotype MEDITERRANEAN SEA • ♂, adult (mounted in glycerine); Cassidaigne Canyon , Station U 07; 43°0′5.940″ N, 5°19′12.510″ E; depth 1056 m; 11 Jan. 2022; CREOCEAN enterprise leg.; ZMB 12957 View Materials ; ZMB. GoogleMaps

Paratypes

MEDITERRANEAN SEA • 2 ♂♂, adult (mounted in glycerine); same data as for holotype.; ZMB 12958 View Materials to 12959 View Materials ; ZMB GoogleMaps • 1 ♀, adult (mounted in glycerine); same data as for preceding; ZMB 12961 View Materials ; ZMB GoogleMaps • 1 ♀, adult (mounted in glycerine); Cassidaigne Canyon , Station U06 ; 43°2′20.352″ N, 5°21′0.096″ E; depth 605 m; 11 Jan. 2022; CREOCEAN enterprise leg.; ZMB 12960 View Materials ; ZMB GoogleMaps .

Description

See Table 2 View Table 2 for a summary of the most relevant measurements of the type material.

Body short (249–310 µm), dorsally curved in holotype and one female paratype (M1 and F1), S-shaped in one male paratype (M2), straight in one male paratype (M3) and ventrally curved in one female paratype (F2). Body slightly tapered towards anterior end (at level of cephalic region) and tail. Width almost uniform over rest of body. Body with 17 well-separated main rings covered by concretion material on annulated body cuticle. Main rings relatively rounded and separated by 3–4 cuticle annules ( Figs 1A View Fig , 2A View Fig , 3A View Fig , 4A View Fig ).

Somatic setae inserted in peduncule and following typical desmoscolecid setal pattern of nine subdorsal and eight subventral pairs (see below). Both subdorsal and subventral setae thick, with cylindrical base and tapering towards distal end. Terminal setae of different shape, with thin and wiry appearance ( Fig. 3D View Fig ). Subdorsal and subventral setae with similar shape and length ( Table 2 View Table 2 ), except for slightly elongated subdorsal setae on 16 th main ring (16 µm) and more elongated subdorsal setae on 17 th ring (17–31 µm).

Nine pairs of subdorsal somatic setae present on 1 st, 3 rd, 5 th, 7 th, 9 th, 11 th, 13 th, 16 th –17 th main rings. One male specimen (M2) has one subdorsal setae located on second ring instead of on third one. Eight pairs of subventral somatic setae located on 2 nd, 4 th, 6 th, 8 th, 10 th, 12 th, 14 th –15 th main rings ( Table 2 View Table 2 ).

Cephalic region globular, moderately wider than long, slightly truncated anteriorly, with distinct lip region. Head cuticle completely covered with concretion material except beneath amphideal fovea. Amphideal fovea covering nearly completely lateral sides of cephalic region. Labial sensilla not detected. Cephalic setae apparently absent, not descirnable in optical microscopy ( Figs 1C View Fig , 3C View Fig , 4B View Fig ). Short cheilostome at level of protruding lip region, leading to short (extending over 2 rings), nearly cylindrical pharynx without posterior pharyngeal bulb ( Figs 1B View Fig , 2B View Fig , 3B View Fig ). In females, intestine with postrectal sac ( Fig. 4A View Fig ) and anal tube protruding from 15 th main ring.

One pair of pigment spots as orange, oval areas with well-defined border, present at level of 4 th –5 th main rings ( Figs 1B View Fig , 2B View Fig , 3D View Fig , 4A View Fig ).

Males monorchic with single testis outstretched and extending anteriorly up to level of 9 th desmos. Spicules (36–39 µm) slightly curved and cephalated. Gubernaculum absent. Cloacal tube broad, opening to exterior on 15 th main ring ( Figs 1B View Fig , 3A View Fig ). Both female paratypes with reproductive system inconspicuous. Even though hard to distinguish, reproductive system of female paratype (F1) didelphic-amphidelphic, with anterior branch extending from base of 7 th main ring and posterior one to 15 th main ring. Vulva appearing at posterior end of 10 th main ring. Oocytes are observed between main rings 11 and 13 ( Fig. 2 View Fig )

Tail with 2 main rings. Last main ring completely covered with concretion material, about 2,5–3 × as long as wide, and composed of wider and cylindrical anterior part with insertion of terminal pair of setae at its base ( Figs 3E View Fig , 4D View Fig ). Posterior part of last main ring strongly curved ventrally. Spinneret minute, not covered with concretion material.

Differential diagnosis

Based on similarities in the number of main rings, the somatic setal pattern, the globular cephalic region and circular amphids, D. (D.) nibelungus sp. nov. is grouped with other 14 species: D. (D.) australicus Decraemer, 1974 ; D. (D.) bathyalis Freudenhammer, 1975 ; D. (D.) borealis Kreis, 1963 ; D. (D.) coronatus Soetaert, 1989 ; D. (D.) galeatus Freudenhammer, 1975 ; D. (D.) gerlachi Timm, 1970 ; males of D. (D.) gladisetosus Timm, 1970 ; D. (D.) lapilliferus Freudenhammer, 1975 ; D. (D.) opacus Bussau, 1993 ; D. (D.) paraleptus Decraemer, 1975 ; D. (D.) perspicuus Freudenhammer, 1975 ; D. (D.) petalodes Lorenzen, 1972 ; D. (D.) rotundicephalus Jung, Kihm & Rho, 2024 ; and D. (D.) yongei Decraemer, 1974 (see Table 3 View Table 3 ). These species share as characteristics having 17 main rings along the body and same somatic setal pattern consisting of 9 pairs of subdorsal setae and 8 pairs of subventral ones. On the other hand, what distinguished D. (D.) nibelungus from the majority of the aforementioned group of species is the apparent lack of cephalic setae and its strongly ventrally curved, beak-shaped tail. The lack of cephalic setae is highly unusual; however, after careful examination of the type material under optical microscopy, no cephalic setae were observed. Desmoscolex (D.) rotundicephalus shares this peculiar characteristic with the species described here, as well as the uncovered lip region, the number of main rings and the somatic setae arrangement. Nevertheless, the somatic setae of D. (D.) rotundicephalus differ in length between subdorsal and subventral, though they share a similar shape. In contrast, the somatic setae of D. (D.) nibelungus are all of similar length, with the last pair exhibiting a wiry appearance. Additionally, the beak-shaped last main ring of D. (D.) nibelungus contrasts with the conical appearance of the last main ring in D. (D.) rotundicephalus .

Apart from differing in the apparent lack of cephalic setae and the particular tail shape, D. (D.) australicus , D. (D.) gerlachi , D. (D.) paraleptus and D. (D.) yongei have subdorsal somatic setae with spatulated or lance-shaped tip, unlike D. (D.) nibelungus sp. nov. ( Timm 1970; Decraemer 1974, 1975). The presence of a long and thin terminal main ring as well as the short cephalic setae with blunt tips ( Freudenhammer 1975) are useful to differentiate D. (D.) bathyalis from the new species described herein. Regarding D. (D.) borealis , it differs from D. (D.) nibelungus sp. nov. in its fusiform body shape and the spinelike setae observed on the 15 th main ring ( Kreis 1963). Both D. (D.) coronatus and D. (D.) nibelungus have a protuding lip region, not covered by concretion material. However, the subdorsal setae of D. (D.) coronatus are slightly longer than the subventral ones, it possesses short cephalic setae and a much shorter spicules in males ( Soetaert 1989) (see Table 3 View Table 3 ).

Desmoscolex (D.) galeatus has cephalic setae and an elongated pair of subdorsal setae on the 13 th and 16 th –17 th rings ( Freudenhammer 1975), unlike D. (D.) nibelungus sp. nov., whose pair of subdorsal setae on the 13 th main ring has average length (see Tables 2 View Table 2 and 3 View Table 3 ). Males of D. (D.) gladisetosus have wiry cephalic setae and a thin and long terminal main ring ( Timm 1970), which differs from the aforementioned features that characterize the new species. Similarly, D. (D.) lapilliferus is notable for its somatic and cephalic setae with a long dark curved tip as well as a long and thin terminal main ring ( Freudenhammer 1975), differing from D. (D.) nibelungus . The cauliflower-shaped cephalic setae of D. (D.) opacus distinguishes it from D. (D.) nibelungus ( Bussau 1993) . Unlike the species described in this study, D. (D.) perspicuus has short somatic setae, increasing in length towards the tail, as well as a long spinneret at its end ( Freudenhammer 1975). Moreover, D. (D.) nibelungus apparently lacks cephalic setae, whereas D. (D.) petalodes possesses cephalic setae with flag-like tip ( Lorenzen 1972).