Mesothuria gargantua Deichmann, 1930

Mesothuria gargantua Deichmann, 1930 View in CoL

Mesothuria gargantua Deichmann, 1930: 95–96 View in CoL , pl. 7, fig. 1. — Deichman, 1940: 191. — Deichman, 1954: 386. — SolÍs-MarÍn, 2003: 168, figs 78–82. — Gebruk et al., 2012: 289–290 View Cited Treatment , fig. 8.

Mesothuria (Allantis) gargantua View in CoL .— Heding, 1940: 333 (list).

Holothuria verrilli Théel, 1886b: 6 (partim).

Material examined. NMV F296863 About NMV * (1) [IN 2021 V 04 031] ; NMV F296873 About NMV * (2), [IN 2021 V 04 046] ; NMV F296880 About NMV (1), [IN 2021 V 04 048] ; NMV F308172 About NMV (1) and NMV F308173 About NMV * (5) [IN 2022 V 08 113] ; NMV F308196 About NMV (1) [IN 2022 V 08 116] ; NMV F308215 About NMV (1) , NMV F308217 About NMV * (1) and NMV F308218 About NMV (3) [IN 2022 V 08 117] ; NMV F308234 About NMV (1) and NMV F308235 About NMV (1) [IN 2022 V 08 124] ; NMV F308236 About NMV * (1), [IN 2022 V 08 126] ; NMV F308252 About NMV (3), [IN 2022 V 08 136] ; NMV F308258 About NMV (2), [IN 2022 V 08 141] ; NMV F308260 About NMV (6) and NMV F308265 About NMV (1), [IN 2022 V 08 143] ; NMV F308296 About NMV (2), [IN 2022 V 08 157] ; NMV F308305 About NMV * (1) [IN 2022 V 08 161] ; NMV F308328 About NMV (9), [IN 2022 V 08 191] .

Diagnosis of IOT material. Conspicuous large white robust species, almost cylindrical but slightly flattened ventrally and tapering to rounded ends (e.g. 195 mm long, 55 mm wide and 55 mm high: NMV F308260 largest specimen in lot, preserved). Skin thick and variably smooth to wrinkled. Mouth subventral to ventral with ~20 tentacles (typically retracted). Terminal anus. Midventral line or shallow furrow, sometimes rust-coloured or pink tinged here and between the wrinkles. Almost complete cover of small cylindrical tube feet, though these are inconspicuous at first glance on larger specimens; slightly larger and more obvious on the posterior part of the ventral surface but can be inconspicuous or absent from the anterior of the same. Skin densely packed with ossicles. Ossicles are large, solid, typically quadri-radiate tables made up of a perforated base disc with low spires made of four (rarely five) pillars, e.g. ~80–109 μm high, joined in one or two places with short spinous tips. Discs irregular and typically 150–190 μm in diameter, but can be larger (up to 280 μm, NMV F308260). Many perforations, typically with inner ring of eight or more larger oval perforations, then more irregular, smaller ones towards the edge. Occasional anastomosing or branching on pillars, and edges of discs not always closed. Tube foot ossicles are similar but slightly smaller.

Remarks. Identifications based on description in Deichmann (1930, 1954) with additional information from the clearer figures of type ossicles redrawn in SolÍs-MarÍn (2003) and subsequently Gebruk et al. (2012). Typically distinguished from other Mesothuria by being large, white and firm, with thick skin and robust, irregular ossicles. Two specimens, NMV F308215 and NMV F308305 (fig. 24e), still grouped genetically with IOT M. gargantua but were smaller with softer wrinkled skin, and ossicles often with slimmer pillars with more elongated spines than other IOT M. gargantua .

Distribution. Atlantic Ocean and Caribbean Sea, Indian Ocean (Australian IOT).

Full bathymetric range. 720–1968 m (IOT 754–1968 m).

Type locality. Caribbean Sea , off Barbados, 720 m.

This species not previously recorded for Australia in AFD or ALA (January 2024). These IOT specimens extend the geographic and bathymetric range for the species (previously to 1347 m in Gebruk et al., 2012) and are the first records for Australia .

References. AFD (2024), ALA (2024), Deichman (1930, 1954), Gebruk et al. (2012), Heding (1940), O’Loughlin (notes and personal correspondence, 2018), SolÍs-MarÍn (2003).