Zygothuria lactea Theel 1886

Zygothuria lactea (Théel, 1886)

(Figures 1 & 2)

Holothuria lactea Théel, 1886: 183 –184, pl. 10, figs. 9 and 15.

Zygothuria lactea; Perrier, 1898: 1665; Gebruk et al, 2012:310 –321, 3 text figs. (synonymy).

Diagnosis (see Deichmann 1954; Gebruk et al. 2012)

Material examined. A32143, west coast of South Africa, between Cape Peninsula and just north of Lambert’s Bay, 32° 28'S, 16° 42'E, Demersal Trawl V279, 11 /01/2012, Trawl 005- 6187, 907 m, 1 spec.; A32144, same locality as spec.1, Trawl 006- 4116, 369 m, 1 spec.

Description. Both specimens poorly preserved. Body oval in live state, sub-cylindrical to oval in preservative. Skin thick, with folds and wrinkles, covered in a slimy coat with very fine adhering sediment and fish scales. Mouth ventral, anus terminal, anal teeth/papillae absent. Colour in life white, almost translucent, white to grey in alcohol. Length up to 83 mm, width of mid-body up to 26 mm. Tube feet very reduced, difficult to discern. Tentacles 20, rounded with 3–4 terminal processes.

A32144—eviscerated, calcareous ring and associated structures lost; gonad and respiratory trees absent; large intestine filling almost entire coelomic cavity. Longitudinal muscles unpaired, thin.

A32143—partially eviscerated, calcareous ring, Polian vesicle, respiratory trees and gonad absent; stone canal attached to dorsal body wall; madreporite small, bean-shaped; longitudinal muscles as in A32144.

Ossicles present in body wall and tentacles only. Dorsal and ventral body wall ossicles comprise triradiate tables with rounded disc (69–134 µm), with irregular margins and with a central hole surrounded by 6-8 large marginal holes; spire with three smooth pillars, terminating in a single point or in three fork-like projections, and a single transverse beam. Tentacle rods short (200-345 µm), margins usually adorned with spines, rarely smooth, medially indented at times.

Distribution (from Gebruk et al. 2012). Cosmopolitan with numerous records from the north-east Atlantic, also known from the north-west Atlantic, off West Africa, south-east Atlantic Ocean, Indo-Malayan archipelago and New Zealand, 694–5278 m.

Remarks. Due to the poorly preserved and eviscerated state of the specimens, it is difficult to make an accurate determination but the specimens come very close to Zygothuria lactea (Théel, 1886) in the general body form and appearance of the tri-radiate tables. While the form of the tables may be identical to those described for the species, the disc diameter is noticeably smaller than that recorded by Théel (disc 200 µm) and Gebruk et al. (disc 150–200 µm). Stellate or hexagonal discs are not obvious and none of the pillars are adorned with spines. This is the first record of tentacle deposits in the species. Tube feet rods reported by Gebruk et al. (2012), Théel (1886) and Mortensen (1927) were not observed. This species has been recorded from the south-east Atlantic Ocean by the ‘Valdivia’ (Heding 1940), about 3000-4000 km off the west coast of South Africa. The current record is therefore the first from truly South African waters; hence some geographic variations between distantly distributed populations (north and mid-South Atlantic and the South African region) must exist with one specimen possessing table spires terminating in a single point only and incomplete discs. These could be attributed to individual or age variations, as one specimen measured 70 mm and the other 100 mm. It does not appear that two species are here represented. The combination Zygothuria lactea (Théel, 1886) has been accepted by WoRMS. The north-east Atlantic variety oxysclera, reported by Perrier (1902) and Mortensen (1927), but rejected by several workers since, has been elevated to full specific status by Gebruk et al. (2012). It is characterised by tables with a meshwork-like holes on the discs and a single-armed spire which is often armed by minute spines. This combination has also been accepted by WoRMS. The specimen with tables with single armed spire, in the current collection, is not ascribed to this species because of the deterioration of most of the table discs.