Molpadia musculus Risso 1826

Molpadia musculus Risso, 1826

Figure 3

Molpadia musculus Risso, 1826: 293; H.L. Clark, 1907: 165, Pl. 11; Pawson, 1977: 100, text-figs: 1, 2, 3, 4a–c, e, Map 1 (synonymy).

Material examined. SAM-A28044, ‘Nansen 404’, Trawl TO16, west coast of South Africa (33° 53.7’S, 17° 26.9’E), 407 m, 10.iv.2007, Louise Lange, 1 spec.

Description. Specimen large, well preserved, barrel-shaped with short tail. Length along ventral surface 80 mm, width of mid-body 15 mm, tail length 2 mm. Colour uniformly violet except at extreme anterior end and the tail which are white to greyish-white. Body wall rough to the touch. Phosphatic deposits abundant (Figure 3 B). Calcareous deposits of body wall delicate, localised mostly in tail and at extreme anterior end, and include fusiform and tri-forked rods, up to 600 µm, with 1 – 4 (usually 3) small central holes and easily fragmented racquet-shaped bodies (Figure 3 A); anchors may be present but only a single broken one detected in the body wall sampled, may be of foreign origin.

Distribution. Essentially cosmopolitan but not yet known from above the Arctic Circle, 35–5205 m. (Pawson 1977)

Remarks. Pawson (1977) revised the molpadiid sea cucumbers of the Southern, Atlantic, Pacific and Indian Oceans, describing four new species and presenting a key to the nine species he recognized as valid. Since then, a few more species have been added. After having examined 170 specimens, Pawson showed that Molpadia musculus is a very varied species with its calcareous deposits changing drastically with age. His synonymy of M. musculus hence appears rather drastic but despite this he comments that it is incomplete “for the limits of variation of the species are far from clearly defined.” (Pawson 1977:100). Based on this, the single southern African specimen, briefly described above, appears referable to this species. It is characterized by the presence of fusiform rods in the body wall, best developed in the tail and much smaller racquet-shaped bodies. Pawson states that anchors, rosettes of racquet-shaped plates and tables with three or more perforations and a solid spire are usually absent in specimens over 30 mm, “having being transformed into very numerous light to dark red phosphatic deposits.”(Pawson 1977:100). Hence the propensity of phophatic bodies and the scarcity of racquet-shaped bodies and spired tables. This is the second record of this species from southern Africa, the first is that of Cherbonnier (1965) from a single 41 mm specimen collected at 480 m from Cabinda (Angola). The South African material differs from Cherbonnier’s specimen by the rarity of racquet-shaped deposits and spired tables, perhaps due to its size and/or age.