Stolus canescens ( Semper, 1867 )

Thandar, Ahmed S., 2019, On some lesser known sea cucumbers in the Natural History Museum, UK (Echinodermata: Holothuroidea), Zootaxa 4688 (3), pp. 361-381 : 365-368

Stolus canescens ( Semper, 1867)

Figures 2 & 3

Cucumaria canescens Semper, 1867: 48 , pl. 13, fig. 6; pl. 14, figs. 3, 9, 10; pl. 15, figs. 2–3.

Stolus canescens Clark & Rowe, 1971: 182 , pl. 29, fig. 7; Liao & Clark, 1995: 497, fig. 301, pl. 13, fig.6.

Material examined. NHMUK 1892.1 .14.27, Holothuria Bank (13 25’ S, 126 0’ E), presented by Lords of the Admiralty, 1 spec.

Description. Specimen fusiform, pentagonal in cross section, U-shaped with an attenuated posterior end; length 35 mm, breadth in mid-body 4 mm. Skin rigid, white in alcohol. Tube feet in rows only in ambulacra, ventral feet longer than dorsal, elongated, in double rows mid-ventrally but reducing to single rows anteriorly and posteriorly. Dorsal tube feet only in single rows per ambulacrum, with one or two also scattered in interambulacra dorso-laterally. Mouth and anus terminal. Anal teeth present but cannot be demonstrated with ease. Calcareous ring complex, radial and interradial plates asymmetrical and fused; radial plates deeply incised, i.e. bifurcating before the posterior margin of the interradial plates; interradial plates with triangular anterior edge; both radial and interradial plates with incipient fragmentation, posterior processes also fragmented. Polian vesicle single and saccate. Stone canal single, short, straight, embedded in dorsal mesentery; madreporite small, oval. Retractor muscles well developed, attached to anterior tip of radial plates of calcareous ring.

Ossicles of body wall circular to oval table-like buttons with undulating margin (51–120 µm, average 69 µm), perforated with 4–8 holes and 9–12 large knobs, with a half ring on one side and a spire on opposite side; spire swollen at base by the characteristic double knobs, usually ending in a single blunt point or usually a tripartite spire with a bi-nodular base bearing a central projection; some buttons without spire and/or half ring. Tube feet tables with curved disc usually perforated by a single hole at each end; spire two-pillared, with or without a horizontal bar, pillars fused for most of their length, ending in a single blunt point. Length of disc 73–108 µm (average 94 µm); height of spire ca. 40 µm. Tentacle stalk contains three types of ossicles: large rods (average length 137 µm), minute rods (average length 86 µm) and rosettes (average 27 µm). Large rods of stalk perforated at ends with short marginal projections; minute rods smooth, rosettes of the closed type. Tentacle branches with both medium to minute rods (26–56 µm, average 40 µm), medium-sized rods delicate, may be perforated at ends; slender rods minute, curved, usually perforated at ends, sometimes branched, branches with or without perforations. Introvert devoid of ossicles.

Distribution. China, Philippines and East Indies ( Liao & Clark 1995) and now Holothuria Bank (Western Australia).

Remarks. This is a well-known West-Pacific form originally described by Semper (1868) from Bohol, Philippines. It is well illustrated by Semper and more recently by Liao & Clark (1995) and its distribution recorded by Clark & Rowe (1971) and Rowe & Gates (1995). However, judging from the literature it has not been encountered frequently. Its most characteristic feature are the large knobs on the buttons, a varying number of marginal knobs and usually a tripartite spire with a bi-nodular base bearing a central projection. Thandar (2005) provides a useful key to the species of Stolus then known.

The above Admiralty Island record is the first record of the species with locality data in the NHMUK online catalogue, last updated 03.02.2017. The existing record is without locality or other data.

Figures

FIGURE 2. Stolus canescens Semper, 1868. Admirality Is. NHMUK 1892.1.14.27. A. Specimen entire; B. Part of calcareous ring; C. Introvert ossicles; D. Rods from tentacle branches; E. Ossicles from tentacle stalk; F. Buttons and plates from body wall; G. Tube feet tables. (All ossicles drawn to same scale). MDIR = mid-dorsal interradial plate.

FIGURE 3. Scanning electron micrograph of ossicles of Stolus canescens Semper, 1868.Admirality Is. NHMUK 1892.1.14.27. A. Tentacle ossicles; B. Tube feet tables; C. Tube foot end-plate; D. Body wall ossicles.