Trachythyone fallax Cherbonnier, 1958

Thandar, Ahmed S., Zettler, Michael L. & Arumugam, Preyan, 2010, Additions to the sea cucumber fauna of Namibia and Angola, with descriptions of new taxa (Echinodermata: Holothuroidea), Zootaxa 2655, pp. 1-24 : 8

Trachythyone fallax Cherbonnier, 1958

Figure 4

Trachythyone fallax Cherbonnier, 1958a: 101 –102, 1 text figure; Cherbonnier, 1965: 6; Massin, 1993: 415, 3 text figures.

Diagnosis (after Cherbonnier 1958a, Massin, 1963, modified herein). Length up to 100 mm. Body form curved. Colour greyish-white in alcohol. Skin thin, rigid, packed with ossicles, large plates imbricating. Tube feet restricted to ambulacra in 1–2 rows, better developed mid-ventrally. Suckers reduced, end-plates absent. Anal teeth absent. Tentacles 10, mid-ventral two reduced. Calcareous ring delicate, radial and interradial plates anteriorly bifid. Polian vesicle and stone canal single. Ossicles of body wall comprise an external layer of deep cup-like baskets (24–60 µm) with a cross-shaped base and 6–8 marginal digitations and an inner layer of smooth multilocular plates of various form and size, 215–700 µm. Tube feet supported by rods (68–420 µm) and small perforated plates, the former curved, with or without perforated ends and with one or more medial projections. Tentacles with straight or curved, perforated rods, similar to those of tube feet.

Material examined. SAM A28096, AHAB-9, stn. -88, Dredge Angola, 7.235° S, 12.684° E, 28.v.2004, 41 m, Forster & Zettler, 1 specimen.

Distribution. West Coast of Africa ( Cabinda, Dahomey, Cameroun, Sierra-Leone, Gabon, N. Angola), 39– 57 m.

Habitat. Sandy substrate.

Remarks. The single juvenile at hand ( Figure 4 A) measures less that 10 mm along the ventral surface, but corresponds well with the description of the species by Cherbonnier (1958a) and Massin (1993), except that the ventral tube feet ( Figure 4 A), because of the juvenility of the specimen, appear mostly in single rows, often zigzag, and the baskets which measure 24–59 µm (mean 33.35 µm, ± 12.67, n = 10) ( Figure 3 B) have only incipient digitations. The plates measure 215–491 µm (mean 331 µm, ± 94, n = 10) ( Figure 4 C), the tube feet rods 68–157 µm (mean 82 µm, ± 25 n = 10) ( Figure 4 D) and there are also small perforated plates in the tube feet ( Figure 4 E). Despite this, the calcareous ring, Polian vesicle and stone canal correspond well with Cherbonnier’s and Massin’s descriptions. Cherbonnier compares his species with the European T. elongata (Düben & Koren, 1844) and concludes that the ossicles are different, the plates of T. fallax being thick and the baskets simpler. T. fallax also resembles T. improvisa (Ludwig, 1875) described from Algoa Bay, South Africa but not found since. However, the baskets of this species are illustrated as being flat and the plates elongated with only two series of holes. T. rigidapeda ( Cherbonnier, 1952) is the only other Trachythyone from South Africa and restricted to the west coast. It differs from T. fallax in the rigidity of its tube feet, the form of the baskets and the slightly-knobbed nature of its plates.

Figures

FIGURE 3. Ocnus paracorbulus n. sp. Holotype, SAM A 28094. A. Tube feet deposits; B. endplate; C. tentacle deposits.

FIGURE 4. Trachythyone fallax Cherbonnier, 1958. SAM A 28096. A. Specimen entire; B. deep baskets from the body wall; C. body wall plates; D. rods from tube feet; E. plates from tube feet.