Psolus imperfectus Clark, 1923

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 : 79

Psolus imperfectus Clark, 1923

( Figure 17 )

Psolus imperfectus H.L.Clark, 1923: 418 .

Psolus imperfectus Deichmann, 1948: 363 , fig. 21, 1–10.

Diagnosis (see Deichmann 1948).

Material examined. SAMC-A 090928 , SM 232, south of Port St. Johns , 32°10.9’ S, 29°10.4’ E, 620– 560 m, 25. VI.1979, 1 spec.

Description. Specimen minute, perhaps immature ( Figure 17A ). Length 5 mm (including tentacles), breadth about 2.5 mm in mid-body. Colour off-white. Mouth terminal, slightly dorsally directed; anus not visible. Specimen flat, dorsal surface only slightly arched, ventral surface flat, left margin folded over a rather indistinct sole, hence ventral tube feet displaced. Only eight tube feet on the right side, about 10 on the left side, few midventrally. Because of deformed nature of the body the lateral tube feet do not appear in single series as some are displaced medially; those on left lateral side protrude, including the two most posterior ones. Dorsal surface without tube feet. Tentacles 10, clearly dendritic, two ventral slightly reduced. Oral valves absent. Dorsal and ventral body wall covered by smooth imbricating plates ( Figure 17B & D ), dorsally up to 80 µm in size, ventrally up to 58 µm. Baskets ( Figure 17G ) common in body wall, minute, with four holes piercing a rather thick base and about 15–16 spines on the rim, pointed in all directions; dorsal baskets up to 40 µm, ventral baskets up to 35 µm. Ossicles of tube feet include large, thick perforated plates and rods ( Figure 17H ), up to 175 µm, plus numerous baskets; the latter apparently larger than those of body wall, and often with more than four basal holes. End-plates reduced ( Figure 17E ), up to 150 µm, not always present. Tentacle ossicles include large thick rods and small smooth plates similar to those of tube feet ( Figure 17C ).

Distribution. South of Port St. Johns to Cape Agulhas, 376– 620 m.

Remarks. The size and form of the animal, the number and distribution of tube feet and the type of body wall ossicles, confirm that this specimen as a juvenile of Psolus imperfectus . It is regrettable that H.L. Clark (1923) neither figured the ossicles nor the animal itself, and perhaps failed to detect any baskets found in association with the plates. His material comprised two juveniles collected off south-east of Cape Agulhas, at 365.76 m (200 fathoms). The holotype which was presumably in the South African Museum could not be located. The paratype from the Museum of Comparative Zoology (Harvard) was studied by Deichmann (1948). Deichmann was therefore the first to find minute baskets, in addition to the plates. Except for the fewer number of holes in the plates of the current material, its baskets are identical to those described by Deichmann (1948). Samyn & Vandenspigel (2016) show some spired scales which were not observed in the South African material. A point of interest is that Deichmann illustrated both smooth and knobbed plates. Despite this the specimen is identified as a juvenile Psolus imperfectus . Deichmann (1948) mentioned the presence of about 20–25 holes in the plates which have a slightly knobbed surface. Clark (1923) also recorded about 20–24 holes, but did not comment on the knobbed plate surface. There is a possibility that the two specimens studied by Clark are perhaps not conspecific with that described by Deichmann and herein. However, the current material with fewer holes in the otherwise smooth plates, appears intermediate in form, perhaps because of its small size. In the absence of the holotype, the specimen must be regarded as a juvenile of P. imperfectus . The type was described from south of Cape Agulhas at about 366 m; hence the current specimen indicates a noteworthy extension of its range eastwards into the warmer waters of the Eastern Cape.

Figures

FIGURE 17. Psolus imperfectus Clark, 1923. SAMC-A090928. A. Specimen (entire); B. Plates from dorsal body wall; C. Rods and plates from tentacles; D. Plates from ventral body wall; E. Developing end-plate from tube foot; F. Developing plate from ventral body wall; G. Baskets from ventral body wall; H. Rods from tube feet of ventral body wall. (B & D same scale; E & F same scale).