Thyone venusta Selenka, 1868

Thandar, Ahmed S. & Rambaran, Ryan, 2015, On some sea cucumbers (Echinodermata: Holothuroidea) from off the south and west coasts of South Africa collected by the South African Environmental and Observation Network (SAEON), Zootaxa 3999 (1), pp. 41-61 : 58-60

Thyone venusta Selenka, 1868

( Fig. 11 )

Thyone venusta Selenka, 1868: 115 , figs. 11 and 12;? Thandar, 1990: 216 –217.

Diagnosis (after Selenka 1868, modified herein). Small species, length up to 85 mm, colour in life brown to orange, fading in alcohol. Calcareous ring complex, tubular. Stone canal and Polian vesicle single. Tube feet scattered throughout ventral and dorsal surfaces, sometime conforming to ambulacra. Ossicles only as tube feet end plates.

Material examined. A31654, South Coast Survey 2011, off Mossel Bay (34° 35'S, 22° 36'E), Demersal Trawl 075-3428, Cruise 273, 103 m, 03/05/2011, R.W. Leslie, 1 spec.

Description. Specimen eviscerated, tentacles, calcareous ring and other associated structures lost. Body Ushaped in live state, cylindrical, slightly curved in preserved state with posterior end turned upwards. Skin smooth, of hairy texture due to numerous scattered podia. Mouth dorsal, anus terminal but dorsally directed. Live colouration orange with white speckles, dorsal surface darker. Preserved colour brown to light orange/off-white, darker anteriorly and posteriorly. Tip of anus white. Length 51 mm, width of mid-body 8 mm. Tube feet scattered throughout ventral and dorsal surfaces, but more prominent in ambulacra. Anal teeth absent.

Respiratory trees paired, right tree extends entire body length, profusely branched, protruding partly through mouth; left tree much shorter, confined to posterior region. Gonadal tubules (testis) unbranched, mature. Longitudinal muscles flattened or slightly rounded. Retractor muscles arise from longitudinal muscles at more or less the same position.

Ossicles absent from body wall, respiratory trees and gonad, only present as tube feet end-plates, better developed ventrally; end-plates simple, irregular with two series of large marginal holes surrounding much smaller central holes without any symmetrical arrangement.

Distribution. Red Sea,?southern KwaZulu-Natal, south coast of South Africa, off Mossel Bay.

Remarks. The form of the body and end-plates strongly correspond with that of the type illustrated by Selenka (1868). However, unlike Selenka’s specimen, anal teeth are absent. Thandar (1990) described a mature female from off the east coast of South Africa, which he identified as T. venusta despite the absence of the calcareous ring, associated structures, end-plates and anal teeth in his specimen. Thandar supported his claim by stating that, like Ohshimella ehrenbergii , it is possible for Selenka’s Red Red species to extend to the southern African coast. He attributed the absence of end-plates and anal teeth to local variations in widely separated populations. However, the current specimen does demonstrate end-plates in the tube feet. Further, Thandar’s specimen was dark brown with purple tips to the tube feet, unlike the white-speckled orange colour of the present specimen. Perhaps this species has various colour morphs but the colour and presence of end-plates demonstrates that the current specimen represents Selenka’s species than the one described by Thandar which may be another species. Selenka recorded the size of the end-plates as 140 µm, which is much larger than that recorded herein (52 µm). It is here speculated that the size of end-plate may be dependent on the size of the tube-foot and the region from which it was removed.

Thandar (1990) synonymised T. venusta with T. okeni Bell, 1884 , based on the general absence of ossicles except for tube feet end-plates in both species and the live colouration of T. okeni as described by Rowe and Doty (1977) in their specimen from Guam. Thandar later examined the type of T. okeni at NHMUK and concluded that both species are not identical and hence the synonymy cannot be upheld as the two species differ in form, size, colouration, calcareous ring and form of end-plates. In fact, Rowe and Gates (1995) treat T. okeni as a distinct species and Arumugam (2011) supported this. It is noteworthy that T. venusta possesses deeply incised radial plates whereas T. okeni possesses posteriorly prolonged radial plates. Recently O’Loughlin et al (2012) also rejected the synonymy.

Figures

FIGURE 11. Thyone venusta Selenka 1868. A 31654 A. Tube foot end plate; B. Tube foot end plate ex Selenka (1868); C. Specimen entire, courtesy Lara Atkinson.