Benthodytes cf incerta Ludwig, 1893

Mackenzie, Melanie, Davey, Niki, Burghardt, Ingo & Haines, Margaret L., 2024, A report of sea cucumbers collected on the first dedicated deep-sea biological survey of Australia’s Indian Ocean Territories around Christmas and Cocos (Keeling) Islands (Echinodermata: Holothuroidea), Memoirs of Museum Victoria (Mem. Mus. Vic.) 83, pp. 207-316 : 231-233

Benthodytes cf incerta Ludwig, 1893

Material examined. NMV F308170 *(1) , NMV F308171 *(1) and NMV F308177 (1) [IN 2022 V 08 113] ; NMV F308197 * (2) [IN 2022 V 08 116] ; NMV F308269 (3) [IN 2022 V 08 145] ; NMV F308327 (1) [IN 2022 V 08 191] .

Diagnosis of IOT material. Large light violet specimens with dark-purple tentacles and tube feet, and some darker purple to maroon-red remnant patches. Elongated, semicylindrical body, highly convex dorsally, clear flattened sole ventrally, rounded anteriorly and rounded to slightly tapered posteriorly. Body solid. Skin thin and firm, thicker ventrally, occasionally more gelatinous, particularly dorsally, and appearing to bubble or form warts in places. Anus dorsal, close to terminal. Mouth ventral with circumoral papillae. Up to 15 peltate tentacles (sometimes 10 or 11). Single rows of up to eight (4 pairs) of well-spaced papillae along dorsal radii, variable size and tapered at ends. Typically, very narrow lateral brim of short, fused tube feet. Midventral tube feet small, in irregular double row, sometimes bare just below the mouth. IOT specimens large (e.g. 230 mm long, 50 mm wide and 35 mm high: NMV F308327 – preserved). Dorsal body wall ossicles large and small crosses, variably thick and thin, typically with distally spinous arms and central apophyses (broken). Arm length variable (e.g. 176–336 μm: NMV F308170), sometimes with corkscrew-like spinous ends. Papillae often same. Smaller crosses typically finer and less spinous, some with no apophyses. Ventral ossicles thick spinous crosses with irregular spinous central apophyses, reduced crosses with and without apophyses, and smooth straight rods with spinous ends. Tentacles straight to curved rods with spinous ends.

Remarks. These specimens vary widely. Specimens match descriptions and illustrations of external morphology for Benthodytes incerta using Hansen (1975), but bipartite apophyses were not seen on crosses (though apophyses were typically broken). Ossicles can key to B. superba , but other features do not match. One specimen ( NMV F308327) has tube feet more “free” than typical when observed in water, and one deeper specimen lot ( NMV F308269 from ~ 3000 m) has a more prominent brim and more “warty” skin than others, but both still fit the general morphology for B. incerta . NMV F308177 is partial (skin only), but skin and ossicles match others in group. Specimens differ from B. marianensis in ossicles and body form, including narrower brim and fewer dorsal papillae. Specimens have a very similar body form to B. manusensis , but with more dorsal papillae, typically a narrower brim, and different ossicles from those shown in Xiao et al. (2018). Most specimens are distinguished also from B. lingua , which is thicker and more gelatinous with no clear ventral sole. One specimen ( NMV F308171) has a B. lingua morphology agreeing with illustrations in Perrier (1902: pl. 12: 1–2), and images of exposed ovaries in Hansen (1975: pl. 12: 2). As discussed under Remarks for the genus, genetics clearly places the specimen with this IOT B. incerta group. Without additional specimens including type material for comparison, we do not attempt to assess the validity of B. lingua as a species. We acknowledge the variation in specimens here and that material potentially represents a new species but identify all to Benthodytes cf. incerta for now.

Distribution. These specimen lots only: Indian Ocean, Australian IOT, Christmas Island and Cocos (Keeling) Islands Territories, Lucia Seamount Stn., Scrooge Seamount Stn., Cocos (Keeling) Stn., and Santa Ridge Stn., 1304–3078 m.

Full bathymetric range. 1304–3078 m.

References. Hansen (1975), Li et al. (2018), Ludwig (1893, 1894), Xiao et al. (2018).