Rholpalodina cabrinovici, Thandar, Ahmed S. & Arumugam, Preyan, 2011

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 : 52-54

Rholpalodina cabrinovici n. sp.

Figures 2 , 4 A–C

Diagnosis. Proboscis and sphere clearly demarcated; reaching approximately 50 mm in total length. Tentacle about 20 in two circles of five large and 15 smaller ones of varying size inside these. Body wall deposits of sphere and proboscis comprise a superficial layer of tables lying outside a layer of large, smooth multilocular, imbricating plates plus other smaller, also multilocular plates interspersed amongst them. Table discs cup-shaped with the rim denticulate and turned up to give to some tables a cup and saucer appearance in lateral view; spire of moderate height, of four pillars, a single cross bar, terminating in a rather ill-defined crown.

Material examined. Holotype, NHM, 1914.12.23.4/5, Lagos, Nigeria, J. Cadman Esq., paratype, same data as holotype., 1 spec.

Etymology. This species is named after Mr. Andrew Cabrinovic of the Natural History Museum, U.K., to acknowledge his logistic support whenever the senior author visited this institution.

Description of holotype. Proboscis and sphere clearly demarcated, without one merging imperceptibly into the other. Holotype, larger of the two specimens, 49 mm in length (proboscis 27 mm, sphere 22 mm), diameter of proboscis 5 mm proximally, 3 mm distally, diameter of sphere 14 mm. Colour, in alcohol, proboscis creamish, sphere creamish-grey proximally, uniformly creamish at base. Tube feet very reduced, in two zigzag rows per ambulacrum, extending to the tip of sphere with mid-ventral ambulacrum crossing pole of the sphere. Mouth and anus set very close together, difficult to distinguish, the latter surrounded by anal papillae. Tentacles about 20, in two circles of five large elongated ones plus about 15 smaller ones of varying size; branches much reduced. Proboscis rigid, sphere not as soft as in other rhopalodinids. Both sphere and proboscis rough to the touch due to the presence of tables superficial to the large imbricating plates whose free ends are directed anterioriad with the perforations so aligned to give the impression of some sort of regular sculpturing on the surface.

Calcareous ring well calcified ( Figure 4 A); radial plates broad, especially proximally with several anterior subdivisions and a slight posterior bifurcation; interradial plates smaller, triangular, broader proximally and narrower distally, with/without posterior indentation. Polian vesicle single; stone canal short, madreporite minute, beanshaped. Each respiratory tree subdivided into two well developed branches of which one is longer and attached to body wall. Gonad (ovary) much branched, full of developing or developed eggs, with the longer branch of the right respiratory tree intermingled with it.

Tables present in both proboscis and sphere lying outside a single layer of multilocular plates. Table discs of proboscis of moderate size (70–109 µm, mean 90.3 µm, ± 13.83, n = 4) ( Figure 2 B), usually rounded with denticulate/spinose margins, turned up to give a saucer-like appearance, with four central holes and several smaller marginal holes in one or two series, rarely the central holes larger than the rest; spire low to moderate, terminating in a rather ill-defined crown; some tables reduced to form fenestrated spheres but these are rare. Discs of the tables of the sphere of similar size (74–119.5 µm, mean 97.5 µm, ± 14.12, n = 10) and form ( Figure 2 D). Plates of the proboscis and sphere imbricating, of various form, circular, oval to elongate, of two distinct sizes, larger plates multilocular with the holes so arranged as to give the skin a characteristic sculpturing-like appearance in surface view. Larger plates of proboscis (1291–1449 µm, mean 1361.6 µm, ± 152.16, n = 10) ( Figure 2 A) with several series of holes; smaller plates (142–270 µm, mean 225.4 µm, ± 43.93, n = 5). Plates of sphere also of two sizes, larger plates (670–1000 µm, mean 891.5 µm, ± 109.27, n = 10) with an irregular margin and often with an indentation for the passage of the tube foot where these are present ( Figure 2 E). Small plates (217–518 µm, mean 386.6 µm, ± 101.27, n = 5) fewer, with fewer holes and uneven margins, dominant at pole of sphere ( Figure 2 C). Tube feet rods of two types, those that are plate-like, multilocular with an elongated portion held at an angle to the main body of the plate and other rods typically of rhopalodinid type, that is curved with/without marginal projections but often with one or more perforations ( Figure 4 B). Tentacle ossicles delicate, comprising rods of varying size and form, no two exactly identical but usually of two types, large ones sparingly perforated with spiny and/or irregular margins, the other curved with one or more marginal projections and terminal holes, resembling such rods of the tube feet.

Paratype not dissected ( Figure 4 C), 45 mm in length (proboscis 21 mm, sphere 24 mm); midventral ambulacrum not clearly discernable at pole of sphere.

Remarks. It is with some hesitation that we describe the two NHM specimens as a new species as they strongly resemble R. pachyderma Panning, 1932 . However, they differ from it in their body form and the reduced denticulations of the table discs and the crowns of the spires. In Panning’s (1932, 1935) drawing of the body form of his species there is no sharp delimitation between the proboscis and the sphere, one is seen to imperceptibly merge into the other. This shape was verified in the type material of R. pachyderma received from the Hamburg Museum. According to Cherbonnier (1958, 1965) his specimens have the same body form as that described for the species by Panning. It is unfortunate that neither Cherbonnier nor Panning, who made in total four descriptions of this species, illustrate the plates of the body wall nor comment on the presence of the smaller plates interspersed between the larger ones, although such plates are present in the type of R. pachyderma we examined. We also failed to find large plates of about 2 mm long as recorded by Panning (1935). For comparative purposes we present here a table ( Table 1 ) comparing the size of the plates of the type recorded by Panning (1935), that of the type measured by us, and those of our new species. Unfortunately, Cherbonnier does not give any measurements of the plates of his specimens.

Cherbonnier records the presence of about 20 tentacles in his 1958 material of R. pachyderma and 25 in his 1965 material. Panning (1932, 1935), on the other hand, makes no mention of the tentacle number of his species.

Figures

FIGURE 2. Rhopalodina cabrinovici n. sp., Holotype, NHM, 1914.12.23.4 / 5. A. Large, elongated plate from the proboscis; B. tables from the proboscis; C. smaller plates from the sphere; D. tables from the sphere; E. large circular plate from the sphere. [Scale: 1 = A, C, E; 2 = B, D]

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.