Plesiocolochirus Cherbonnier, 1946

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 : 22-24

Plesiocolochirus Cherbonnier, 1946

Figure 1 ; appendices 1, 2

Acolochirus H. L. Clark, 1946: 395 .— Panning, 1971: 41 (synonymy by Rowe in Rowe & Gates 1995)

Apentacta H. L. Clark, 1946: 395 (synonymy by Panning 1971, and Clark & Rowe 1971)

Plesiocolochirus Cherbonnier, 1946: 286 .— Panning, 1949: 448– 449.— Panning, 1971: 42.—Rowe (in Rowe & Gates), 1995: 277.

Type species. Plesiocolochirus spinosus ( Quoy & Gaimard, 1834) (original designation)

Type species locality. Eastern Australia, New South Wales, Port Jackson .

Otherassignedspecies(withtypelocalityadded). Plesiocolochirus armatus (Marenzeller von, 1881) ( China); P. australis ( Ludwig, 1875) (NE Australia, Bowen); P. challengeri ( Théel, 1886) (N Australia, Torres Strait); P. dispar ( Lampert, 1889) (NW Australia, Mermaid Strait); P. ignavus ( Ludwig, 1875) (S Australia, Gulf St Vincent); P. inornatus (Marenzeller von, 1881) ( China); P. minaeus sp. nov. (NW Australia, Camden Sound, below); P. minutus ( Ludwig, 1875) (NE Australia, Bowen); P. tessellarus ( Cherbonnier, 1970) ( Mozambique Channel).

Diagnosis (sensu stricto, based on type species only, described below). Body firm, packed with calcareous ossicles, fusiform with upturned oral and anal ends, long posterior taper, body oval in mid-body section, axial (not curved) length up to 64 mm; lateral edges of body with prominent, firm, conical papillae with imbricating scales; five conical oral valves, with imbricating scales distally; anal cone with large imbricating scales distally, large non-imbricating scales anterior to imbricating ones; small anal scales; small ossicles clustered into contiguous lumps in mid-body to create pseudo-scales, each with central passage/perforation for withdrawn tube feet, pseudo-scales about 1.00 mm across. Ten dendritic tentacles, 8 large, 2 small. Calcareous ring cucumariid-like, plates solid, higher than broad, lacking posterior prolongations. Tube feet scattered irregularly over body, inconspicuous, small, appear to penetrate pseudo-scales, more numerous ventrally than dorsally, mid-ventral radius with irregular paired rows, narrow space on each side of mid-ventral radius lacking tube feet.

Three intergrading ossicle forms of body wall:

1. surface layer of finely knobbed, shallow bowls, variably bridged across margins to sometimes create hollow, irregular, ellipsoid-like ossicles;

2. layer of flat, thickly knobbed buttons, some developing secondary layers to become small scales;

3. deeper layer of multi-layered scales.

Lateral papillae and tube feet with terminal endplates. Tentacle ossicles rods; lacking rosettes.

Remarks. Cherbonnier (1946) proposed that the following species be assigned to his new genus Plesiocolochirus : Colochirus challengeri Théel, 1886 ; Colochirus gazellae Lampert, 1889 (subsequently referred to Loisettea Rowe & Pawson, 1985 ); Colochirus inornatus von Marenzeller, 1881 ; Thyone papillata Sluiter, 1887 (subsequently referred to Stolus Selenka, 1867 ); Colochirus squamatus Sluiter, 1901 (subsequently synonymised with Colochirus robustus Östergren, 1898 by Rowe in Rowe & Gates 1995).Subsequently other species have been assigned to Plesiocolochirus : Colochirus armatus Marenzeller von, 1881 ( China); Colochirus australis Ludwig, 1875 (NE Australia, Bowen); Colochirus dispar Lampert, 1889 (NW Australia, Mermaid Strait); Cucumaria ignava Ludwig, 1875 (S Australia, Gulf St Vincent); Plesiocolochirus minaeus sp. nov. (NW Australia, Camden Sound, below); Colochirus minutus Ludwig, 1875 (NE Australia, Bowen); Pentacta tessellara Cherbonnier, 1970 ( Mozambique Channel).

Rowe (in Rowe & Gates) 1995 referred Ocnus occiduus O’Loughlin & O’Hara, 1992 to Plesiocolochirus , with reservations. This species was subsequently referred to Australocnus O’Loughlin & Alcock, 2000 . In the same work Rowe judged that Colochirus minutus is a junior synonym of Plesiocolochirus australis . We provisionally raise Colochirus minutus out of synonymy for further consideration.

Phylogenetic data based on CO1 sequences ( Figure 1 ) recover a clade of six species that appear to correspond to Plesiocolochirus : P. challengeri (N Australia); P. ignavus (SE Australia); P. minaeus sp. nov. (below) (NW Australia); P. tessellarus ( Comoros) ; Plesiocolochirus species 1 from NW Australia and Palau; Plesiocolochirus species 2 from NE Australia. The two unassigned species are close to specimens that have frequently been referred to Plesiocolochirus australis and Plesiocolochirus minutus , as well as to Colochirus sp. 1 mentioned above. A detailed study of these species, including study of relevant type specimens, is needed to determine the identity of these species and morphological boundaries of the Colochirus – Plesiocolochirus complex.

Unfortunately genetic data are not currently available for Plesiocolochirus spinosus , the type species of the genus. Morphologically this species is close to Plesiocolochirus challengeri . We anticipate from morphological observations that Plesiocolohirus spinosus , Plesiocolochirus challengeri , Loisettea amphictena Rowe & Pawson, 1985 and Loisettea gazellae will fall together in a clade distinct from the remaining species assigned to Plesiocolochirus .

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

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

2. presence of numerous inter-radial tube feet;

3. presence of knobbed button body wall ossicles;

4. absence of tentacle rosette ossicles.

Determination of the morphological limits of the clades corresponding to these genera awaits further study.

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%).