Crucella scotiae ( Vaney, 1906 )

Thandar, Ahmed S., 2019, On some lesser known sea cucumbers in the Natural History Museum, UK (Echinodermata: Holothuroidea), Zootaxa 4688 (3), pp. 361-381 : 363-365

Crucella scotiae ( Vaney, 1906)

Figure 1

Thyone scotiae Vaney, 1906: 400–401 , fig. 1; Ekman, 1925: 106–108, fig. 24.

Ypsilocucumis scotiae Panning,1949: 455 ; Pawson, 1969: map 3.

Caespitugo citriformis Gutt, 1990: 105 , figs 1, 5–7, table 2; 1991:324.

Crucella cf. hystrix Gutt, 1990 . O’Loughlin et al., 1994: 552, table 2.

Crucella scotiae O’Loughlin et al., 2009: 10 , table 1.

Material examinedl. Cape Adare , 13–18 m, Sir George Newnes, 2 spec.

Description. Specimen cylindrical and slightly U-shaped, with tapered end more so posteriorly. Larger specimen 54 mm in length and 15 mm in breadth in mid-body, smaller specimen 50 mm in length and 19 mm in breadth in mid-body. Skin yellowish-cream in alcohol (live colouration pink all round according to uncatalogued NHMUK collection from South Orkney, at 20–30 m). Tentacles 10, colour cream, ventral two slightly reduced. Dorsal and ventral surfaces and ambulacra and interambulacra not easily distinguishable. Tube feet short, retractile, scattered, more numerous in ambulacra of ventral surface; suckers of more or less same diameter as tube feet. Faint longitudinal lines mark position of the longitudinal muscle bands. Mouth and anus terminal; anal teeth absent, special anal papillae present. Calcareous ring simple, radial and interradial plates fused, even ventrally. Radial plates longer, anteriorly bifid and proximally narrow, each with deep groove for insertion of retractor muscle. Interradial plates triangular and sharply pointed. Posterior end of ring undulating. Polian vesicle single, long, extending beyond midbody. Stone canal remarkably reduced; madreporite arises directly from water ring (not detected in second specimen dissected). Each respiratory tree with paired, well ramified branches, terminal branches elongated and tube-like; right tree longer, both trees unite before opening into cloaca. Cloaca elongated, suspensor muscles prominent. Gonad absent in dissected specimen. Longitudinal muscles well developed, unpaired. Retractor muscles thick, arising from longitudinal bands anteriorly, more posteriorly in the ventral ambulacra, but dorsally almost in line with calcareous ring.

Ossicles of body wall simple plates of various shapes but often circular or oval. Smaller plates (100–233 µm, average 155 µm) smooth with fewer holes. Larger plates (210–287 µm, average 243 µm) usually knobbed with numerous holes and often with a mesh-like superstructure partially covering the plate, but never developed as a spire. Ventral ossicles smaller and less numerous than dorsal, also as simple knobbed plates of varying shapes. Ossicles of tube feet very reduced curved rods. End plates non-contiguous, circularly arranged pieces giving the impression of disintegration. Tentacle ossicles (95–295 µm, average 187 µm) as simple plates with irregular margins and few holes, some plates rod-like but always perforated. Introvert ossicles as simple rods (175–440 µm, average 264 µm), some Y-shaped, L-shaped or X-shaped with no ornamentation, but often branched.

Distribution. Circumpolar ( O’Loughlin et al., 2009), perhaps to 100 m depth.

Remarks. It is with no hesitation that the above material is referred to Crucella scotiae ( Vaney, 1906) . It perfectly satisfies the description of the type material. However, the generic position of this species is questionable since the genus Crucella was established by Gutt (1990) for an Antarctic cucumariid whose body-wall ossicles are usually cruciform plates bearing a secondary meshwork partially covering the plates and often produced into a tall superstructure resembling a spire. Although O’Loughlin et al. (2009) referred Vaney’s species to this genus because of a secondary meshwork on some ossicles, none of the ossicles described by Vaney (1906) nor those in the current material are cross-shaped or have a spire-like superstructure. However, O’Loughlin et al. (2009) do state that C. scotiae has “body-wall ossicles as small-knobbed plates, large irregular thick knobbed perforated plates with secondary mesh thickening; posterior body with multi-layered ossicles ( O’Loughlin 2009 et al.: 10). It is for this reason that the diagnosis of the genus is here changed to accommodate this species and its like. The above synonymy given is that of O’Loughlin et al. (2009). The species comes quite close to C. citriformis ( Gutt, 1990) , especially in its form, tube feet distribution and most body-wall plates. However, in its calcareous ring, tube feet deposits and the type of end plates, composed of non-contiguous, circularly arranged pieces, it closely resembles C. hysterix , the type species of the genus.

The specimen here described is the first record of the species in the NHMUK judging from its online catalogue.

Figures

FIGURE 1. Crucella scotiae (Vaney, 1906), Cape Adare. A. Specimen entire; B. Calcareous ring; C. Tube feet rods, D & G.. Large plates from body wall; E. Simple plates of dorsal body wall; F. Knobbed plates of body wall. H. Tentacle plates (C–F drawn to same scale). MDIR = mid-dorsal interradial plate.