Pseudocolochirus unica ( Cherbonnier, 1988 )

Thandar, Ahmed S. & Samyn, Yves, 2004, Taxonomy of the monotypic genus Koehleria Cherbonnier, 1988 (Echinodermata: Holothuroidea: Cucumariidae), Zootaxa 652, pp. 1-11 : 3-9

Pseudocolochirus unica ( Cherbonnier, 1988) (comb. nov.)

(figs 1, 2)

Koehleria unica Cherbonnier, 1988: 178 , figs 75A–L.

Material examined. Republic of South Africa (Sodwana Bay, 2­Mile Reef), 10.ii. 2001, 12 m depth, coll. Y. Samyn, RMCA 1731 / RSAKZN/0157 (1 specimen).

Description. Specimen well preserved; mouth anterior, tentacles extended; anus posterior, dorsally directed. Length (excluding tentacles) 32 mm; width of mid­body 10 mm; height 12 mm. Colour of dorsal surface, in alcohol, beige­brown with dark speckles and other dark blotches arranged in two irregular series of 3–4 pairs; ventral surface off­white to yellowish. Body wall moderately thick (<1 mm), only slightly rough to the touch. Podia in two rows in ambulacra, also scattered in interambulacra of especially mid­ventral surface where they appear in more than two rows; dorsal interambulacra also with numerous, scattered, papilliform podia. Anteriorly, podia well­developed in five groups around mouth, each group with 4–8 podia. Tentacles 10, only four partially extended, wellbranched, all of more or less equal size (ventral two slightly smaller), dark brown in colouration. Anus terminal, star­shaped, surrounded by minute, conical anal teeth.

Calcareous ring (fig. 1H) well developed, low, simple, without posterior prolongations; radial and interradial plates of more or less equal size, anterior projections of radial plates with a deep groove for attachment of retractor muscles; posterior margins of all plates notched, those of interradials deeper and more pronounced. Polian vesicle single, elongated, about 8 mm long, with dark brown streaks. Stone canal single, short, twisted in dorsal mesentery; madreporite four­lobed (fig. 1J). Introvert retractor muscles well developed, originating as single strands from the longitudinal muscles in anterior third of body, more posteriorly in the ventral ambulacra. Gonad well developed, tubules straight, unbranched, full of sperm, filling most of posterior half of body cavity. Respiratory trees richly branched, reaching anterior end of body, both trees arise independently from narrow, slightly elongated cloaca.

Ossicles of dorsal and ventral body wall (figs 1A, B, C; 2A, B, D) similar in size and shape, increasing in length antero­posteriorly (tables 1, 2), comprising simple, thick, perforated rods or plates with spiny or serrated margins, holes variable in number and usually small in diameter, frequently occluded.

TABLE 1. Dorsal deposits of Pseudocolochirus unica ( Cherbonnier, 1988) ; s.d. = standard deviation, n = number of ossicles measured.

Dorsal deposits

Anterior Mid Posterior

length width holes length width holes length width holes

(m) (m) (m) (m) (m) (m)

mean 215,7 128,1 6 279,1 149,3 8,1 329,8 153,1 9,8

s.d. 26,4 25,9 1,6 46,6 23,2 2,4 61,3 24,8 3,1

n 30 30 30 30 30 30 30 30 30 Ventral deposits

Anterior Mid Posterior Dorsal deposits 165–475 m long, 85–190 m wide, with 3–21 holes (figs 1A; 2A). Ventral deposits 175–390 m long, 85–220 m wide, with 4–15 holes (figs 1B; 2D). Ventral body wall also with few other reticulated rosace­like plates, up to 420 m in size, with irregular margins and numerous holes (figs 1C; 2B). Podia with simple, slightly spiny rods (figs 1F; 2E) with one or more perforations at each end, suckers strengthened by wellformed end­plates (figs 1G; 2C). Tentacle deposits include rods and rosettes ( Figs 1 D, E; 2F, G); rods 150–250 m long, straight or slightly curved with one or more perforations at each end; rosettes 20­40 m long, in the form of branched rods or crinkly corpuscles (tab. 3). Introvert without ossicles.

Ecology. The specimen was found under a large coral block, at 12 m depth, in association with Holothuria (Mertensiothuria) hilla Lesson. Cherbonnier (1988) reported that the holotype was recovered from the cryptofaunal crevices of the reef flat of Tuléar, during ebb tide. It thus seems that this species is fugitive rather than fossorial.

The cryptic behaviour and the small size of the species make it difficult to find; as such commenting on its rarity is currently impossible.

Remarks. This is only the second specimen of P. unica (Cherbonnier) . In general its internal and external morphology and its ossicle assemblage correspond well with the original description. The observed differences are the following: (i) the holotype has a uniform yellowish colouration while our specimen is mottled with dark spots and irregularly arranged blotches; (ii) the holotype possesses two Polian vesicles while we observed only a single one; (iii) the holotype’s madreporite is described as spherical, while in our specimen it is distinctly four­lobed ( Fig. 1 J); (iv) the introvert retractor muscles of the holotype are described as being special, each consisting of two discrete, thick strands; in the present specimen the retractor muscles are simple and not divided; (v) the holotype is reported without anal teeth, whereas in the present specimen minute anal teeth were observed. However, the overall ossicle assemblage of the holotype corresponds remarkably well with what is reported here, both in structure and in dimensions, although it must be noted that in Cherbonnier’s (1988) description, the ossicles from the podia have, in the text, been confused with those from the tentacles (see Cherbonnier 1988: 179, fig. 75 L for tentacle and not podia deposits and compare with figs 1E, 2F in our description).

The above differences are intraspecific variations within P. unica , since it has been evidenced that in many taxa the colouration and number of Polian vesicles are variable characters. Regrettably, since little or no data exist as to the taxonomic significance of the form of the madreporite (see also Deichmann 1948) and the branching­off points of the retractor muscles, we cannot comment on these differences, as they may be specimenrather than species­specific.

In order to judge the status of the genus Koehleria , we first need to position it within the higher­level taxonomy of the Cucumariidae , the family in which Cherbonnier (1988) quite correctly placed Koehleria . In this family, Pawson & Fell 1965 recognise three subfamilies: Cucumariinae Ludwig, Colochirinae Panning and Thyonidiinae Heding & Panning. Of these only the first two include ten­tentacled species. The Colochirinae, in addition, are characterised by species which possess complete or incomplete baskets in the body wall, while the Cucumariinae lack baskets in their body wall, at least in their adult stage ( Thandar 1991). Cherbonnier (1988), who refrained from assigning subfamilies, implied that Koehleria is classified within the Cucumariinae by stating that it comes closest to Pseudocolochirus . The latter is classified in the Cucumariinae (see Thandar 1991). However, we believe that the characters used by Cherbonnier (1988) to erect his new genus are inadequate. Cherbonnier only commented that Koehleria differs from Pseudocolochirus in the “forme si particulière des spicules” and the absence of anal teeth. In this study, we have shown that unica does have anal teeth and that the ossicle assemblage it presents is similar to that of P. violaceus . As such, we believe that the genus Koehleria is invalid and must best be regarded as a junior subjective synonym of Pseudocolochirus .

Table 4 summarizes the ossicle assemblage of the two species now recognized in Pseudocolochirus .

Figures

FIGURE 1. Pseudocolochirus unica (Cherbonnier, 1988) from South Africa. Ossicles. A. from dorsal body wall; B. from ventral body wall; C. rosace­like reticulated plate from ventral body wall; D. minute rods and rosettes from tentacle; E. large rods from tentacle; F. ventral podia deposits; G. podia end­plate; H. calcareous ring (r = radial plate; ir = interradial plate); J. stone canal and madreporite.

Tables

TABLE 4. Ossicle assemblage of P. u n i c a (Cherbonnier, 1988) and P. violaceus (Théel, 1886). The differences are mainly in size and in abundancy of dorsal ossicles in P. violaceus and the smoothness of its plates.

Ossicle assemblage	P. unica (Cherbonnier, 1988)	P. violaceus (Théel, 1886)
dorsal body wall	thick perforated rods or plates with serrated to spiny rim; mean length 274 mm; mean width 143 mm; holes per ossicle 3–21, fre­ quently occluded	ossicles scarce or absent
ventral body wall	similar in size (mean length 284 mm; mean width 138 mm; holes 4–15) and shape as those of dorsal body wall, but few reticu­ lated rosace­like plates (diameter up to 420 mm) with irregular margins and numerous holes also present.	scarce, thick, subcircular to elongated perforated rods or plates with slightly knobbed or smooth margin; mean length ± 114 mm; mean width ± 70 mm; average number of holes per ossicle 9; anal end with reticulated rosette­like plates (diameter roughly 220 mm) with irregular margins and numerous holes
ventral podia	simple, slightly spined rods with one or more perforations at each end or small mul­ tilocular plates with spiny margins	perforated rods to irregular multilocular plates with corrugated/crinkly margin
tentacles	rods and rosettes	rods and rosette­derived plates
introvert	no ossicles	no ossicles