Plesiocolochirus tessellara ( Cherbonnier, 1970 ) Cherbonnier, 1970

Thandar, Ahmed S., 2006, New species and new records of dendrochirotid and dactylochirotid holothuroids (Echinodermata: Holothuroidea) from off the east coast of South Africa, Zootaxa 1245, pp. 1-51 : 30-33

Plesiocolochirus tessellara ( Cherbonnier, 1970) comb. nov.

Figure 10

Pentacta tessellara Cherbonnier, 1970:282 , fig. 2 (A–O); Thandar, 1991:123, fig. 8 (A–J). Colochirus minutus Macnae & Kalk, 1958:130 (non Ludwig, 1875).

Type

MNHNP.

Distribution

Only known from Mozambique and east coast of South Africa.

Habitat

Coral, rock.

Remarks

This species was assigned to Pentacta by both Cherbonnier (1970) and Thandar (1991). However, Rowe (in Rowe & Gates 1995) restricted the genus Pentacta to include only the type species, Actinia doliolum Pallas, 1766 and perhaps Cucumaria capensis Theel, 1886 a. He characterised the genus as having podia restricted to the ambulacra ventrally but scattered dorsally, ten tentacles of more or less equal size and spicules comprising multilocular, knobbed plates and shallow, rugose baskets with basic quadrilocular design. These characters still present a problem as in some specimens of P. doliolum the two ventral tentacles or some others may be reduced and the podia in C. capensis are confined to the ambulacra and not dorsally scattered. However, both these are endemic southern African temperate species (shallow­water and deep­water respectively), not known to extend into the warmer subtropical waters of KwaZulu­Natal. P. tessellarus , on the other hand, is from tropical­subtropical waters and has the ventral surface somewhat sole­like with prominent podia, the ventral­most two tentacles reduced and a brittle body wall packed with spicules comprising multi­layered scales, nodular perforated plates and simple shallow baskets. These characters accord well with those of Plesiocolochirus enunciated by Rowe (in Rowe & Gates 1995). However, the genus Plesiocolochirus was initially erected for only the type species, P. spinosus (Quoy & Gaimard) characterised by evenly distributed radial and interradial podia, latero­ventral tubercles and radial plates of the calcareous ring bearing distinctive paired posterior prolongations(see Cherbonnier 1946; O’ Loughlin & Alcock 2000). Hence the generic placement of P. tessellarus in Plesiocolochirus is problematic. It is here only tentatively referred to this genus until a more suitable genus is found to accommodate it.

This species, originally known only from Mozambique, is well described by Cherbonnier (1970). Thandar (1991) examined a paratype of the species and provided measurements of its spicules. The current material is the first record of the species from South Africa. The two specimens here examined are obviously juvenile, judging from their size (28 mm & 35 mm), distribution of podia, state of development of the tentacles and calcareous ring, and the absence of the gonad. Both are white in alcohol with a yellowish tinge at the anterior end of the larger specimen, and hence differing in colour from that recorded for the species by Cherbonnier (!970) and Thandar (1991) ­ perhaps due to depth, age or preservation. The tentacles are retracted in both specimens, the anus encircled by minute teeth in the larger specimen, and the podia restricted to the ambulacra, better developed ventrally in 1–2 rows per ambulacrum but in single row in each dorsal ambulacrum. The skin is rough to the touch and the imbricating plates easily visible with a stereoscope.

The body wall spicules comprise baskets (15–25 µm, mean 19 µm), always provided with small nodules on the surface and a spinous or “jagged” rim ( Figure 10 D, E); buttons (75–95 µm, mean 86 µm) that are small, medium to large­ knobbed ( Figure 10 A, B); and large (405–475 µm, mean 433 µm) imbricating, multi­layered, knobbed plates/scales ( Figure 10 C). The podia are supported by: elongated, slightly curved rods (112–287 µm, mean 199 µm) with several perforations and often with a distinct knobbed surface ( Figure 10 G); baskets (16–29 µm, mean 20 µm), similar to those of the body wall ( Figure 10 F); and perforated smooth to knobbed plates (39–116 µm, mean 65 µm) ( Figure 10 H). The dorsal endplates are circular with large central holes and a single series of peripheral holes ( Figure 10 I), whereas the ventral endplates are larger (136 µm cf. 120 µm), multi­lobed ( Figure 10 J), with similar arrangement of holes except that instead of a single series of holes on the periphery there are numerous small holes in the lobes. The tentacle stalk contains elongated, delicate rods (39–90 µm, mean 65 µm) with few holes ( Figure 10 L) whereas perforated plates (87–184 µm, mean 154 µm) occur in the branches ( Figure 10 K). No rosettes were detected in the tentacles, nor any deposits in the introvert.

The present specimens differ from the type material in size, colouration, distribution of podia, poor calcification of the calcareous ring, absence of rosettes in the tentacles and lack of spicules in the introvert. These can be attributed to the immaturity of the material and hence here considered to be of no taxonomic significance.

Thandar (1991) commented that this species comes quite close to Pentacta minuta (Ludwig) (junior subjective synonym of Plesiocolochirus australis according to Rowe (in Rowe & Gates 1995), originally described from North Australia but also recorded by Macnae and Kalk (1958) from Inhaca Island ( Mozambique) as Colochirus minutus , on material identified but not described by Cherbonnier. Regrettably this material is no longer extant. Hence, P. minuta ( Macnae & Kalk, 1958, non Ludwig, 1875) is here relegated to the synonymy of P. tessellarus .

Figures

FIGURE 10. Plesiocolochirus tessellarus (Cherbonnier, 1970). SAM­ 27909. A. large­knobbed buttons from dorsal body wall; B. side view of buttons; C. plate / scale from dorsal body wall; D. baskets from dorsal body wall; E. side view of baskets from dorsal body wall; F. baskets from dorsal podia; G. rods from dorsal podia; H. small­knobbed plates from dorsal podia; I. end­plate from dorsal podium; J. part of end­plate from ventral podium; K. plates from tentacles; L. tentacle rods. A­C & G­L scale a; D­F scale b.