Rholpalodina parvalamina Cherbonnier, 1965

Thandar, Ahmed S. & Arumugam, Preyan, 2011, On some rhopalodinid sea cucumbers in the collections of the Natural History Museum, U. K. (Echinodermata: Holothuroidea: Dactylochirotida), Zootaxa 2982, pp. 49-58 : 54-57

Rholpalodina parvalamina Cherbonnier, 1965

Figures 3 , 4 D

Rhopalodina parvalamina Cherbonnier, 1965: 665 , 1 text-fig.

Diagnosis (after Cherbonnier 1965, amended herein). A rhopalodinid holothuroid with a sharp distinction between the proboscis and the sphere, 25–30 mm long. Tentacles 15. Anal papillae well developed. Tube feet often reach ventral pole of sphere. Deposits of body wall plates and tables. Plates of proboscis large, up to about 700 µm, imbricating, multilocular, often with a few tiny nodules at one end. Plates of sphere small (up to +/- 450 µm), button-like with four or more holes. Tables of proboscis small, discs up to 100 µm, with spinose margin. Tables of sphere larger, up to 165 µm, with irregular discs and denticulate crowns.

Material examined. NHM, 1957.7.2.56, off West Africa, A.R. Longhurst Coll., 2 specimens identified as Rhopalodina labeniformis (sic) Gray.

R. pachyderma (Type) R. pachyderma (Type) R. cabrinovici n. sp. ex Panning 1935 (our measurements)

Description. Of the two specimens the larger one is complete, measuring about 25 mm in length with a 13 mm proboscis ( Figure 4 D); the other is only 16 mm with a 3 mm incomplete proboscis. Mouth and anus set close together; tentacles 15 (8 large + 7 small); anal papillae well developed. Tube feet minute, in two zigzag rows per ambulacrum, some reaching the ventral pole of sphere, sparsely distributed in some parts of sphere.

Plates of proboscis slightly imbricating but this is not obvious, large (558–667 µm, mean 623 µm, ± 44.4, n = 5), multilocular, round to oval with an undulating margin and without a superstructure but often with a few small nodules at one end ( Figure 3 A). Plates of sphere mostly quadrilocular, much smaller than those of the proboscis (206–433 µm, mean 298.9 µm, ± 62.3, n = 10), though a few multilocular ones do occur ( Figure 3 C). Tables of proboscis small, with spinose to slightly knobbed, rounded disc (82–97 µm, mean 89.9 µm, ± 5.19, n = 10) with a somewhat serrated margin, four central holes and usually four, sometimes more, peripheral holes; spire of four-pillars with distorted crowns, perhaps due to corrosion ( Figure 3 B). Tables of the sphere larger, with smooth, irregular disc (118–162 µm, mean 136.4 µm, ± 14.7, n = 10) with several peripheral holes and also with a poorly developed spire ( Figure 3 D). Tube feet deposits include typical curved rods of the rhopalodinid type (up to 178 µm) with spinose margins ( Figure 3 F) as well as irregular, multilocular plates (289–500 µm, mean 390.7 µm, ± 69.1, n = 6) ( Figure 3 E). Tentacle deposits similar to those illustrated by Cherbonnier (1965).

Remarks. This species was described by Cherbonnier (1965) from a single specimen collected from the coast of Cameroon at 17 m. As is usual of him, his description is complete. It is only with slight hesitation that we refer the two NHM, UK specimens to this species. One is the poor development of the spires of the tables and the other being the absence of an arch covering some of the holes on the proboscis plates as described for the type. The former may be due to the dissolution of the top of the spires and the latter as individual variation. Cherbonnier also does not comment on the definite size distinction between the tables of the sphere and the proboscis but his drawings allude to this difference.

Cherbonnier compares his species to R. lageniformis Gray and R. pachyderma Panning and distinguishes it from the latter on the basis of tube feet and tentacle deposits. However, this species can clearly be distinguished from other species of the genus by the differences in structure and size of both the tables and the plates of the proboscis and the sphere except for R. gracilis Panning. The latter species is, however, characterized by 20 tentacles and the equal dominance of large and small plates in the sphere, which also possesses tables with large, often cruciform discs.

Figures

FIGURE 3. Rhopalodina parvalamina Cherbonnier NHM, 1957.7. 2.56. A. Elongated plates from the proboscis; B. tables from the proboscis; C. smaller, rounded plates from the sphere; D. tables from the sphere; E. irregular plates from the base of the tube feet; F. rods from the tube feet. [Scale: 1 = A, C, E; 2 = B, D, F]

FIGURE 4. Rhopalodina cabrinovici n. sp., NHM, 1914.12.23.4 / 5. A. Calcareous ring; B. rods from the tube feet; C. Paratype, specimen entire; D. Rhopalodina parvalamina Cherbonnier, NHM, 1957.7. 2.56, entire.