Heterocucumis steineni ( Ludwig, 1898 )

Thandar, Ahmed S., 2019, On some lesser known sea cucumbers in the Natural History Museum, UK (Echinodermata: Holothuroidea), Zootaxa 4688 (3), pp. 361-381 : 377

Heterocucumis steineni ( Ludwig, 1898)

Figure 9

Cucumaria steineni Ludwig, 1898: 30–32 , pl. 2, figs 22–24; Ekman, 1925: 38–45, fig. 6; Ekman, 1927: 363, 390–393, figs 12, 13.

Cucumaria antartica Vaney, 1906: 6–10 , figs 3, 8, 26; Vaney, 1908: 427; Vaney, 1914: 89.

Heterocucumis steineni Massin, 1994: 13 , figs 5–16; O’Loughlin, 2002: 317.

Ekmocucumis steineni Pawson, 1969 : pl. 22, map 4.

Ekmocucumis sp. MoV 2005, O’Loughlin et al., 1994: 551–554.

Material examined. NHMUK 1911.11 .24.1, South Georgia, Criuckohauk Collection , 1 spec.

Description. Specimen cucumber-shaped with anterior end slightly turned upward and narrower than posterior end. Skin smooth, colour cream in alcohol. Length 43 mm, breadth in mid-body 15 mm. Tube feet in double rows in ambulacra, ventral tube feet more pronounced. Mouth and anus terminal; anal teeth absent. Calcareous ring lacking. Polian vesicles four, of variable length, short, vermiform, shortest 3 mm, longest 30 mm. Stone canal short, free, straight; madreporite spherical, hanging free in coelom. Left respiratory tree well branched, reaching mid-body right tree shorter, poorly branched. Gonad in single tuft, gonadal tubules unbranched, some full of eggs, apparently tubules maturing at different times. Longitudinal muscles well developed, unpaired. Retractor muscles thick, dorsal ones arising from posterior end of body, ventral ones slightly more anteriorly, all attach to introvert.

Ossicles of body wall consist of large (133–443 µm, average 343 µm) perforated, spinous plates with serrated margin; plates vary in shape from circular to triangular. Ossicles of tube feet comprise plates of varying shape (190– 367 µm, average 273 µm), either with/without spines and 2–10 perforations, sometimes more. End plates spinous, with numerous small perforations. Tentacle ossicles comprise perforated plates and rods varying from circular to triangular, (133–307 µm, average 234 µm), circular plates with more perforations. Introvert ossicles absent.

Distribution. Subantarctic.

Remarks. Because of the changes in the form of the ossicles with age this species has a chequered history and hence a long list of synonyms. It was Massin (1994) who cleared up the mess by comparing a series of growth forms and excellently illustrating the body wall, tube feet and tentacle ossicles at different stages of growth. The identification of the current material is based on the analysis of Massin (1994). The single specimen measuring about 50 mm presents ossicles identical with those from similar-sized specimens illustrated and discussed by him. The current specimen, judging from the NHMUK online catalogue, is the first record of this subantarctic species in its collection.

Figures

FIGURE 9. Heterocucumis steineni (Ludwig, 1898). A. Specimen entire; B. Tentacle plates, C. Ossicles of anal region; D. Plates of dorsal body wall; E. Plates of tube feet; F. SEM body wall ossicles; G. SEM portion of tube feet end- plate (B–E All drawn to the same scale).