Psolidium acorbulum Thandar, 2006

Thandar, Ahmed S., 2018, On some miscellaneous sea cucumbers (Echinodermata: Holothuroidea) in the collections of the South African Museum with three new species, Zootaxa 4532 (1), pp. 57-85 : 78-79

Psolidium acorbulum Thandar, 2006

( Figure 16 )

Psolidium acorbulum Thandar, 2006: 39 , fig.13.

Samyn & VandenSpiegel, 2016:487, text-fig. 27. Diagnosis (see Thandar 2006)

Material examined. SAMC-A 090927 , SM 123, off south of Scottburgh , 30°33.04’ S, 30°48.06’ E, heavy dredge, 690 m, 10.V.1977, 1 spec .

Description. Form typically psolid with an arched dorsal surface and flattened ventral surface forming the sole which is largely covered by ventral flaps of the body wall; sole thin-walled, membranous. Specimen length about 2.5 mm, width in mid-body just over 1 mm. Colour off-white in alcohol. Dorsal scales overlapping, not possible to determine the number of scales between mouth and anus as latter two not apparent. Dorsal tube feet in three conspicuous rows, but few also in inter-ambulacra. A single row of tube feet present on margin of sole. Tube feet emit from between scales and not through them. Tentacle number undetermined, tentacles simple (digitate) or very finely branched. Internal anatomy typical of species, form and size of ossicles as in type. Dorsal plates ( Figure 16A ) include large type, up to 335 µm and small type, up to 70 µm, all with about 10 holes. Ventral plates ( Figure 16B ) much smaller, larger ones up to 240 µm, and smaller ones up to 135 µm, all with up to 10 holes, usually fewer. Tube feet deposits comprise minute perforated plates ( Figure 16C ), larger ones up to 350 µm, smaller ones up to 90 µm; end-plates present, up to 100 µm, with numerous holes.

Distribution. East coast of South Africa, from Scottburgh to East London, 690–775 m, perhaps extending to N. Mozambique.

Remarks. This species was originally based on two specimens collected from off Port St. Johns and East London area on the east coast of South Africa. Now, its occurrence north of Port St. Johns is a noteworthy extension of its range. This species was described by Thandar (2006) and therefore only a few pertinent features are recorded above. The knobs on the plates are not as prominent as in the type. It is also difficult to determine the tentacle number and form. Simple tentacles were described for the type where as in the current specimen some tentacles appear minutely branched. Despite this there is no doubt as to the specific identity of the current material. As in the type the form is exactly psolid-like and the mouth and anus not distinguishable as they are both covered by overlapping scales.

Figures

FIGURE 16. Psolidium acorbulum Thandar, 2006. SAMC-A090927. A. Dorsal body wall plates; B. Ventral body wall plates; C. Plates from tube feet; D. Fragmented end-plates.