Havelockia, Pearson, 1903

Thandar, Ahmed S., 2019, On some lesser known sea cucumbers in the Natural History Museum, UK (Echinodermata: Holothuroidea), Zootaxa 4688 (3), pp. 361-381 : 373-375

Havelockia ? quadruperforata ( Cherbonnier, 1954)

Figure 7

Thyone quadruperforata Cherbonnier, 1954: 252 ; 1955: 166–167, pl 41, fig. a–h).

Material examined. 1960.5.21.2, Mumbai (Bombay), 1 spec.

Name-bearing type. MNHN. Paris .

Type locality. Djibouti in the Aden Gulf .

Description. Single individual partially eviscerated, introvert and calcareous ring still attached to body. Form U-shaped, off-white in colour. Length along ventral surface 8 mm, breadth in mid-body 2 mm. Introvert and calcareous ring desiccated, hence number of tentacles and form could not be determined without further damage to specimen. Tentacles appear rather translucent and poorly branched. Calcareous ring fragmented in two parts (possibly due to previous study), clearly of the sclerodactylid type, forming a short tube, well separated from the introvert; radial and interradial plates unfragmented, artificially cracked and weakly fused, both clearly bifid anteriorly and more or less of same height and width; radial plates deeply incised posteriorly, paired radial processes distally curled and approximately four times the length of ring, processes obviously fragmented. Stone canal single, short, free; madreporite apparently multilobed. Gonad (testis) well developed, tubules short, unbranched, filled with gametes.

Body-wall ossicles comprise mostly robust tables (88–101 µm, average 96 µm) with usually a quadrilocular disc and short arched spire which appears as a smooth handle on one side, holes of disc rarely more than four, with additional holes usually small and placed at the ends of disc. Tube feet tables with a straight or slightly curved disc (51–85 µm, average 74 µm) and a low spire, which may or may not be arched and terminating in 1–2 teeth. Regrettably most tube feet tables corroded and hence exact form is difficult to appreciate; disc apparently with four central holes and usually one or more holes at ends. End plates absent. Tentacles comprise poorly developed, partially corroded, mostly broken rods. Introvert deposits tables (average 53 µm) with multilocular disc of various shapes but with ill-formed spire.

Distribution. Perhaps Indo-West Pacific but so far only recorded from Djibouti in the Indian Gulf and now Mumbai, West India and perhaps the Arabian Sea, judging from some material at the NHMUK identified as Thyone cf. quadruperforata by Ms. Ahearn.

Remarks. Cherbonnier (1954 & 1955) based this species on two specimens (10 and 8 mm in length) collected from Djibouti in the Aden Gulf. He described his material as having a simple calcareous ring but because of the form of the ossicles placed the species in Thyone with a query. The simple calcareous ring described by Cherbonnier (1955) was perhaps due to its underdevelopment or damage; even in the current specimen the calcareous ring is fragile, in two parts and somewhat detached from the introvert. The writer studied the type specimens at MNHN and found that both specimens lacked not only the calcareous ring but also ossicles. A subsequent study of several specimens from Oman in the Arabian Sea collected in 1991, in the collections of NHMUK, identified by Ms. Ahearn as T. cf. quadruperforata , confirmed Ahearn’s suspicions that they are not identical to Cherbonnier’s species. These are here included with the single specimen identified as? Thyone sp. in the current NHMUK material here referred to as T. cf. quadruperforata described below and should be included with it. Although the largest specimen in this collection has a complex calcareous ring with poorly fragmented plates and short processes, their tentacle ossicles are different from those illustrated for the type described as plates and hence cannot be identical with Cherbonnier’s (1954) species. Regrettably Cherbonnier did not examine the introvert ossicles. Even the three specimens labelled as T. cf. quadruperforata by Ms. Ahearn, and examined by the writer at the USNM also lacked a calcareous ring but their ossicles were identical to those of the NHMUK specimens from Oman, except that some tables had slightly knobbed margins on the disc and some tube feet tables had an arch on the opposite side of the spire. Despite the fact that the plates of the calcareous ring are not fused for most of their length, they are compact, not subdivided, and the body-wall tables are quadrilocular, both T. quadruperforata and T. cf. quadruperforata are here transferred to the genus Havelockia in the family Sclerodactylidae . It is regrettable that Arumugam (2011) only commented on this species, but excluded it in her treatment of Havelockia and Thyone , clearly influenced by the simple nature of the calcareous ring described by Cherbonnier (1955) for the holotype.

Figures

FIGURE 7. Havelockia?quadruperforata Cherbonnier. 1954. Mumbai. A. Specimen entire; B. Part of calcareous ring; C. Introvert ossicles; D. Tube feet ossicles, E–F. Body wall ossicles. (All ossicles to same scale); MDIR = mid-dorsal interradial plate.