Pseudostichopus profundi Djakonov, 1952

O'Loughlin, P. Mark & Ahearn, Cynthia, 2005, A review of pygal-furrowed Synallactidae (Echinodermata: Holothuroidea), with new species from the Antarctic, Atlantic and Pacific oceans, Memoirs of Museum Victoria 62 (2), pp. 147-179 : 176

Pseudostichopus profundi Djakonov, 1952

Pseudostichopus profundi Djakonov, 1952: 127–129 , figs 15–18.

Material examined. Syntype ( RAS). Russia, SE of Kamtchatka, 52°45'N, 161°41'E, 4100–4200 m, 25 Jul 1946 .

Description. Up to 56 mm long; body cylindrical; body wall thick, opaque, soft; few sand grain attachments; very small tube feet unevenly distributed all over body, lengths variable, largest anteriorly and posteriorly, fewest mid-dorsally and midventrally; 20 tentacles; radial plates of calcareous ring lacking "teeth"; longitudinal muscles cylindrical; gonad tubules unbranched; tentacle ossicles thick, broad, bent, irregular, variably perforated, somewhat mesh-like, typically 200 µm long; tube feet ossicles variable from irregular rods, to knots, to irregular curved mesh-like narrow plates, up to 180 µm long; posterior lobes with rare unbranched rods, irregular ends, up to 0.17 mm long; gonad and respiratory trees with small, smooth, sparse rod fragments.

Colour. Body and tube feet brown to grey.

Distribution. Russia, SE of Kamtchatka, 4100–4200 m.

Remarks. The description above is based on Djakonov (1952). The syntype that was examined here was 27 mm long, and very soft. The longitudinal muscles were rounded laterally, but broadly attached to the body wall and not cylindrical, and are considered here to be flat. No gonad was found. The pygal tube feet were soft, cylindrical, and typically 0.3 mm long, 0.15 mm diameter. No ossicles were found in the tube feet. The absence of ossicles in the tube feet, and flat longitudinal muscles, suggest that the syntype examined here is not conspecific with P. profundi as described. Djakonov (1952) described very small, smooth rods in genital tubules and respiratory trees. We judge these to be probably artefacts and not ossicles, since such very small fragmentary rods are frequently present in gonad and respiratory tree preparations.

Reference by Djakonov (1952) to cylindrical longitudinal muscles and unbranched gonad tubules indicate an appropriate assignment of the species to Pseudostichopus . But the flat longitudinal muscles, and absence of prominent tube feet on the paired radii, indicate that the syntype examined here belongs in Molpadiodemas . The characters of the species, and generic assignment, remain unresolved.

Amongst Pseudostichopus species the unique character of P. profundi (as described by Djakonov) is the presence of curved mesh-like narrow plates in the tube feet.