Thyone avenusta 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 : 5-7

Thyone avenusta Cherbonnier, 1970

Figure 1

Thyone avenusta Cherbonnier, 1970: 286 , fig 4 A–M; Thandar, 1990: 214, fig. 5 a–g; Cherbonnier, 1988: 197, fig 85 A–M.

Type

MNHNP.

Type locality

Morrumbene, Mozambique, 35 cm.

Previous South African record

None

Material examined

SAM — A23721, R.V. ‘Meiring Naude’ St. XX 94, 30 13.8’ S, 30 54.2’ E, between Green Point and Widdenham, KwaZulu­Natal, 8.vii. 1986, 70 m., 1 spec.

Description

Specimen small, slightly curved with anterior and posterior ends turned upwards; length 11 mm, breadth in mid­body about 3.5 mm; colour, in alcohol, uniformly white with a slight tinge of yellow at the extreme anterior end. Mouth and anus terminal. Tentacles retracted; anal teeth distinct, flanked by subterminal podia. Dissection revealed 10 whitish tentacles ­ eight elongated but of unequal size, ventral two much reduced. Podia well developed, especially ventrally, where they are arranged mostly in the ambulacra with a few also scattered in the interambulacra; suckers of ventral podia with diameter much larger than that of podia; dorsal podia shorter, scattered. Body wall thin, soft.

Calcareous ring ( Figure 1 I) well developed, extremely long, reaching almost twothirds length of body from anterior end; total length of ring, including introvert, ca. 6.5 mm, tubular, with the radial plates deeply incised, i.e. bifurcating before the posterior border of the interradial plates; both radial and especially interradial plates broken into a mosaic; anterior projections of all plates of more or less equal length, with those of the radials being bifid for the attachment of retractor muscles, posterior processes of radial plates distally curved and fragmented into a single series of segments. Polian vesicle single, elongated. Stone canal single, short, straight and free, terminating in cotyledonous madreporic body ( Figure 1 J). Respiratory trees well branched, both uniting before opening into an elongate cloaca. Gonad immature, in two tufts of unbranched, white tubules. Longitudinal muscles unpaired, retractor muscles well developed, originating from longitudinal muscles in anterior third of body, more anteriorly in the ventral ambulacra.

Spicules of body wall comprise typical Thyone tables ( Figure 1 A) with small discs (38–48 µm, mean 44 µm) with smooth or slightly spinose margins and perforated by 4–5 (occasionally 6) large holes; spire short (33–43 µm, mean 38 µm), two­pillared, terminating in a crown of teeth usually developed as two clusters; spire sometimes reduced to knobs on surface of disc. Podial deposits comprise few tables, numerous rods and an endplate ( Figure 1 D). Tables ( Figure 1 B) usually with an irregular disc (ca. 50 µm long), pierced by more than four holes, and a short, occasionally arched spire provided with tuberosities; rods ( Figure 1 C) 62–76 µm (mean 69 µm), slightly curved with smooth margins and perforated by 1–3 holes at each end; endplates of the ventral podia better developed than dorsal (105–129 µm, mean 119 µm cf. 86–91 µm, mean 89 µm), with small holes in the centre, larger ones outside these in a single series, and small ones outside these in one or two concentric series. Tentacles supported by curved, elongated, slender rods (49–110 µm, mean 79 µm) ( Figure 1 H) with one or more perforations at expanded and/or digitated ends, other smaller rosettes­like rods (35–52 µm, mean 44 µm) ( Figure 1 F) as well as by rosette­shaped bodies (22–34 µm, mean 28 µm) ( Figure 1 G), quite unlike the typical rosettes of the introvert. Introvert spicules developed only as closed rosettes (22–34 µm, mean 29 µm) ( Figure 1 E).

Distribution

Madagascar, Mozambique and east coast of South Africa, up to 70 m.

Habitat

Mangrove, sand.

Remarks

The specimen at hand corresponds well with the description of the type given by Cherbonnier (1970), except that the podial deposits comprise, in addition to a few characteristic tables, also large curved rods. Thandar (1990) examined a single specimen of this species that was part of the type­material and found body wall tables with up to 16 holes on the discs, no rods in the podia and recorded the presence of anal teeth, reported as absent in the type. Thandar concluded that these differences were perhaps age variations as the type measured only 30 mm whereas his specimen was 47 mm, with spicules restricted to the posterior end. The present specimen is also small (11 mm) and hence its body wall tables are similar to those of the type, both in size and the number of holes in the disc. The presence of rods in the podia may be a juvenile feature. A characteristic of this species is the presence of three types of spicules in the tentacles (smooth rods, rosette­like rods, and rosettes). T. avenusta can be confused with T. propinqua Cherbonnier, 1970 because of its characteristic four­holed table discs but the latter species has plate­like spicules, instead of rosettes, in the introvert and large multilocular rods in the tentacles. The present specimen, the first record of this species from South Africa, taken at a depth of 70 m, is the deepest yet recorded for the species as the type came from mangrove off the Mozambican coast while the Madagascar material was taken from the reef at Tuléar.

Figures

FIGURE 1. Thyone avenusta Cherbonnier, 1970. SAM­A 23721. A. tables from body wall; B. tables from dorsal podia; C. perforated rods from dorsal podia; D. end­plate from dorsal podium; E. rosettes from introvert; F. rosette­like rods from tentacle; G. rosettes from tentacles; H. rods from tentacles; I. calcareous ring; J. madreporite. A­H scale a.