Echinocucumis M. Sars, 1859

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 : 210

Genus Echinocucumis M. Sars, 1859

Diagnosis (amended from O’Loughlin et al., 2015). Mid-body sub-spherical, tapered non-retractile oral and anal ends, usually upturned; calcareous ring cucumariid-like, lacking posterior prolongations; tentacles ten, digitiform, unequal in size; tube feet slender, restricted to ambulacra, can be discrete, sparse, or absent; body invested with large imbricating scales that are single-layered perforated plates, each scale with predominantly one tall spine typically arising near plate margin.

Remarks. Echinocucumis has previously been recorded from the Atlantic, Pacific, Indian, and Southern Oceans including Antarctica with eight currently accepted species. Only one species – E. ampla – was found in the IOT, previously recorded from the Southern Ocean and off the eastern coast of Australia. Diagnosis from O’Loughlin et al. (2015) amended to include discrete tube feet and to allow for variation in spine placement on ossicles as not all are marginal.

Echinocucumis ampla O’Loughlin and Skarbnik-López in O’Loughlin et al., 2015

Figure 2a–f, Appendix 1, Table S1.

Echinocucumis ampla O’Loughlin and Skarbnik-López, 2015: 77–

80, tables 1, 2, 5, 6; figs 1, 7, 8.— O’Hara et al., 2020: 10, fig. 5, table S1. Dactylochirotida sp. nov. (HOL 10).— Hibberd and Moore, 2009:

119, 146.

Material examined. NMV F296861 (1) [IN 2021 V04 031] ; NMV F 308161 (1) [IN 2022 V08 105] .

Diagnosis of IOT material. Small, white, u-shaped species with prominent belly mid-body. Anterior variably upturned and slightly tapered to a rounded oral end, posterior tapered to upturned tail. Skin thin, brittle, parchment like and often “prickly”, particularly on ventral surface, due to the complete cover of imbricating spined scales. Tentacles retracted here but typically ten digitiform of irregular length and supported by curved rod ossicles. Ventrolateral tube feet in sparse, paired rows (fig. 2c). Body wall ossicles were broken in these specimens but show single-layered perforated plates with a single large composite spire greater than 200 μm high and typically marginal sometimes central on plates (fig. 2d, e). Broken solid plates (fig. 2f) were also observed in perianal ossicle samples. Preserved specimens from IOT up to ~ 25 mm long (lateral width, tentacles withdrawn) and 10 mm high mid-body (NMV F308161).

Remarks. Presence perianally of solid plates was considered a diagnostic character for this species (Mark O’Loughlin, pers comm., 2018). They were seen in this material (fig. 2f) but without the occasional small, spaced perforations expected. The original species description does not include tube feet for the larger (65 mm long) specimen, but the possibility of their presence was raised in “Remarks” ( O’Loughlin et al. 2015). In specimens from the eastern Australian abyss subsequently identified as E. ampla by O’Loughlin, tube feet were evident in smaller specimens, but rarely in larger specimens (Mark O’Loughlin, pers comm., 2018). Here we report the presence of ventrolateral tube feet, clearly observed in these small IOT specimens when viewed under a microscope (fig. 2c). Only 16S sequence data is available for this species ( Table S3). It was recovered in a clade representing the family Ypsilothuriidae .

Distribution. Southern Ocean ( O’Loughlin et al., 2015), South Pacific (eastern coast of Australia, see below), and Indian Ocean (Australian IOT, this work).

Full bathymetric range. 557–4139 m (IOT 2189–2435 m).

Type locality. Southern Ocean , southern Kerguelen Plateau northeast of Heard Island, 708 m.

This species was not recorded from Australia in AFD prior to January 2024, but was recorded from off the eastern coast in ALA (January 2024) from Freycinet in Tasmania to the Coral Sea in Queensland at 1006–4139 m. This IOT material represents a geographic range extension for the species .

References. AFD (2023), ALA (2024), O’Loughlin et al. (2015), O’Loughlin (notes and personal correspondence, 2018), Rowe et al. (2017).