Rhopalodina lageniformis Gray, 1853

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 : 50-52

Rhopalodina lageniformis Gray, 1853

Figure 1

Rhopalodina lageniformis Gray, 1853: 301 –302; Panning, 1932 (synonymy); 362–372, plates 1 & 2; Panning 1935 (synonymy): 24–27; Cherbonnier, 1958: 294; 1965: 10; Heding, 1937 (passim): 36–39,

Diagnosis (amended herein). A medium-sized rhopalodinid holothuroid (holotype 42 mm in length); proboscis and sphere clearly delineated. Tentacle number approximately 20 (15 + 5). Radial plates of calcareous ring with short paired posterior prolongations and several anterior incisions. Pedicels may or may not traverse ventral pole of sphere. Body wall deposits include tables, normally restricted to sphere (absent in the holotype) and multilocular plates. Table discs with crenulated or smooth margins; spire of moderate height (± 90 µm), of four pillars, with/ without crossbars, usually terminating in a ring or cluster of few to many spines. Plates thick, delicate, smooth, with/without super-structure; non-spired cruciform plates present at pole of sphere. Pedicels with curved or elongated, plate-like rods.

Material examined. Holotype NHM, UK, 1938.8.23.67, Congo Expedition.

Remarks. Rhopalodina lageniformis was described by Gray (1853) from a single specimen collected from the Congo. Gray commented that the whole of the internal organs appeared to be destroyed, either by diluted alcohol or by evisceration, and that the animal was so compressed leaving no internal cavity. However, on careful examination Gray determined that the body form of his unique specimen was ovate with a slight keel on each side. The holotype of the species at NHM, UK is in an excellent state of preservation and the “keel” is not obvious. However, it lacks internal organs thus corroborating Gray’s observations.

Gray’s description of the species is superficial. Since then this species was described by Semper (1868), Ludwig (1877, 1889), E. Perrier (1886), Panning (1932, 1935), Heding (1937, passim) and Heding & Panning (1954). It is not clear from these works whether anyone re-examined the holotype for we have failed to find any descriptions or illustrations of its calcareous deposits. In addition, the number of tentacles and the form of the calcareous ring of the type remain undetermined. Semper (1868), whose description of the species is quite detailed, illustrates just one table and one pedicel rod of his material which he identified as R. lageniformis . The only reasonable illustrations of the deposits of presumably this species are those of Panning (1935) but once again not from the type but from some materials in the Hamburg Museum. The tentacle number of this species has been worked out by Heding (1937) and the calcareous ring illustrated by both Semper (1868) and Heding (1937).

We hence provide descriptions and figures of the calcareous deposits of the type but did not dissect it to determine the tentacle number and the form of the calcareous ring. We are in no position to determine whether the identifications of materials of the above authors to R. lageniformis are correct, since several variations from the type have relatively recently been described as new species by Heding (1937), Panning (1935) and Cherbonnier (1965, 1988).

The external morphology of the type is adequately described by Gray. It is here noted that the tube feet, which are restricted to the sphere, are almost threadlike (filiform), and up to 2 mm in length, with an expanded terminal sucker. Contrary to Heding’s (1937) observations, and Thandar’s (2001) reiteration of the characteristic of Rhopalodina , the tube feet of the mid-ventral ambulacrum clearly traverse the ventral pole of the sphere as they do in both Rhopalodinopsis Heding and Rhopalodinaria Cherbonnier , the other two genera of the family. Since tube feet at the pole of the sphere are also present in other species of Rhopalodina , namely R. cabrinovici n. sp., R. pachyderma Panning and R. parvalamina Cherbonnier , Rhopalodina cannot now be characterized as lacking tube feet in the pole of the sphere. Despite this, the polytentaculate genera Rhopalodina and Rhopalodinopsis are still valid, characterised by the clear separation of the mouth and anus in the latter and their close association as to be almost indistinguishable, in the former. In addition, the numerous, non-imbricating, small knobbed, minute plates of the sphere in Rhopalodinopsis are very distinctive and there are rosette-shaped granules in the tentacles.

The proboscis also bears sparse outgrowths which may be either reduced tube feet or epizoons. The length of the proboscis is 29 mm, and the entire animal, including the sphere, is 42 mm. These measurements are slightly smaller than those recorded by Gray and can be attributed to subsequent shrinkage.

Both the proboscis and the sphere of the type are characterized by large imbricating, round to oval, multilocular, smooth plates, with those of the proboscis ( Figure 1 A) being slightly smaller than those of the sphere ( Figure 1 C) (proboscis plates 301–586 µm, mean 436.5 µm, ± 72.88, n = 10; sphere: 457–561 µm, mean 509.3 µm, ± 34.78, n = 10). These measurements are much smaller than those recorded by Panning (1935) who reports a maximum diameter of over 1 mm for both the proboscis and sphere plates. The holes of the plates are fairly large, measuring up to 56 µm and 70 µm in diameter in the proboscis and sphere respectively. Despite numerous attempts we found no tables in either the proboscis or the sphere and no evidence that these were dissolved in the preserving fluid. No ossicles, except some broken rods were detected in the tube feet ( Figure 1 B) but no clues to betray their original structure. We also found no evidence of any end-plates. Panning (1935) report some cross-shaped, perforated, spired plates from the pole of the sphere in his material. We also find similar plates in the pole of the sphere of the type but their spires are not obvious ( Figure 1 E).

Figures

FIGURE 1. Rhopalodina lageniformis Gray, Holotype, NHM, 1938.8. 23.67. A. Plate from the proboscis; B.? tube feet deposits; C. plate from the sphere; D. plates from the pole; E. cross-shaped plates from pole.