Colochirus Troschel, 1846

O’Loughlin, P. Mark, Harding 1, Caroline & Paulay, Gustav, 2016, The sea cucumbers of Camden Sound in northwest Australia, including four new species (Echinodermata: Holothuroidea), Memoirs of Museum Victoria 75, pp. 7-52 : 16-18

Colochirus Troschel, 1846

Figure 1 ; appendices 1, 2

Colochirus Troschel, 1846: 64 .— Semper, 1867: 56.— Ekman, 1918: 5–6.— Panning, 1949: 439.— Panning, 1971: 42–43, fig. 5.— Liao & Clark, 1995: 474.—Rowe (in Rowe & Gates), 1995: 272.

Type species. Colochirus quadrangularis Troschel, 1846 (monotypy)

Other currently assigned, accepted species (with type locality added). Colochirus crassus Ekman, 1918 ( NW Australia; junior synonym Colochirus quadrangularis var. australoides Panning, 1949 by Rowe in Rowe & Gates 1995); C. cylindricus Semper, 1867 (Philippines) ; C. pusillus Helfer, 1912 (Gulf of Suez); C. robustus Östergren, 1898 (S Korea; junior synonym Colochirus squamatus Sluiter, 1901 by Rowe in Rowe & Gates 1995).

Diagnosis (sensu stricto, based on type species only, described below). Body quadrangular in mid-body section, slightly tapered towards oral and anal ends; body and papillae firm, densely packed with ossicles; preserved length up to 98 mm, dorsal and ventro-lateral radii slightly raised, each with prominent, conical papillae in irregular zig-zag rows; five oral valves, each with a terminal papilla and sometimes 1 or 2 additional papillae; five anal scales, some small peri-anal papillae, 5 longer proximal anal radial papillae. Ten dendritic tentacles, 8 large, 2 ventral small. Calcareous ring plates not forked posteriorly, lacking posterior prolongations. Dorsal and lateral inter-radii lacking tube feet; tube feet in discrete bands in ventro-lateral and mid-ventral radii, each band about 4 podia wide, ventral inter-radii usually lacking tube feet, inter-radii similar in width to the radial bands of tube feet.

Ossicles of body wall of six recognizable but inter-grading forms:

1. small, shallow bowls, margin smooth to finely knobbed or finely spinous, variably bridged across margins or not;

2. abundant rounded-rectangular to oval to irregular shallow bowls, one short or long margin prominently spinous, bowls variably partly bridged or not;

3. some rounded-rectangular to oval larger shallow bowls, sometimes partly bridged; 4. larger shallow bowls bridged on one side to create smooth, hollow, irregular ellipsoids;

5. shallow bowls, frequently thick-walled, bridged to create irregular ellipsoids with inner bridging, not hollow;

6. enlarged inner-bridged ellipsoids inter-grade with multi-layered scales.

Tentacle ossicles rod-plates, rods, rosettes.

Remarks. Rowe (in Rowe & Gates 1995) restricted Colochirus to three assigned species Colochirus crassus , C. quadrangularis and C. robustus , leaving the status of C. cylindricus , C. pusillus and C. viridis Semper, 1867 (considered to be nomen dubium) as uncertain, as they were not assigned to other genera.

With the support of CO1 sequence data ( Figure 1 ), we confirm Ekman’s report (1918) of the occurrence of Colochirus robustus in NW Australia.

A phylogenetic analysis based on CO1 sequence data shows that species currently assigned to Colochirus and Plesiocolochirus fall in two well-supported clades ( Figure 1 ). The Colochirus cluster includes Colochirus quadrangularis (from Singapore, near the type locality, and across tropical Australia), Colochirus robustus (from NW Australia and the Philippines), and Colochirus species 1 (from N Australia, Japan, the Philippines, and Madagascar). This unassigned species is morphologically close to specimens that have frequently been identified as Plesiocoloshirus australis ( Ludwig, 1875) . After examining type material, Rowe (in Rowe & Gates 1995) synonymised Colochirus minutus Ludwig, 1875 with Plesiocolochirus australis ( Ludwig, 1875) . We hope to examine the type specimens of both of these species and then be in a position to assign the unidentified Colochirus species in a subsequent work.

Panning (1971) observed that some shallow bowls (up to 107 µm long) were bridged on both sides to create irregular ellipsoids with an inner shallow bowl layer, and thus not hollow. We have not been able to support this observation by Panning (1971) as all solid ellipsoids appear to be built up on the concave side only of the shallow bowls with the outer surface supported by an inner network. Shallow bowls bridged on one side only but without an inner bridging network create irregular hollow ellipsoids. We note that Cercodemas anceps Selenka, 1867 has deep bowls that may be bridged to create such more regular hollow ellipsoids.

Colochirus Troschel, 1846 (type species Colochirus quadrangularis Troschel, 1846 , above) is distinguished sensu stricto from Plesiocolochirus Cherbonnier, 1946 (type species Plesiocolochirus spinosus ( Quoy & Gaimard, 1834) , below), by:

1. absence of large imbricating external scales on distal anal cone, on proximal oral valves, and on lateral papillae;

2. absence, usually, of inter-radial tube feet;

3. absence of knobbed single-layered button ossicles in the body wall;

4. presence of tentacle rosettes.

Figures

Figure 1. Maximum likelihood tree of Colochirus–Plesiocolochirus COI data, with mid-point rooting. Bootstrap support (100 replicates) indicated by circles (100%) and rectangles (>95%).