Mesothuria cathedralis Heding, 1940

Mesothuria cathedralis Heding, 1940 View in CoL

Mesothuria (Allantis) cathedralis View in CoL — Heding, 1940: 336–338, textfig. 5.

Mesothuria (Penichrothuria) cathedralis View in CoL .— Heding, 1942: 8–9, textfig. 8, figs 1–5; Non Mesothuria (Allantis) candelabri View in CoL .— Heding, 1940: 334–335, textfig. 3, figs 1–6.

Mesothuria cathedralis View in CoL .— Gage et al., 1985: 196.— Gebruk, 2008: 50, 51.— Gebruk et al., 2012: 284 View Cited Treatment , 286–289, fig. 7.— Rogacheva et al., 2013: 592.— Gebruk et al., 2014: 169.

Material examined. NMV F308202 About NMV * (4) [IN 2022 V08 116] ; NMV F308237 About NMV (1) [IN 2022 V08 126] .

Diagnosis of IOT material. Small Mesothuria species, elongated cylindrical to oval shape, slightly flattened ventrally, with soft, wrinkled, cream-grey to light brown skin, sometimes with a pink tinge. Mouth subventral. Tentacles retracted in IOT specimens and not dissected, but ~20 expected. Anus terminal. Scattered cover of papillae and tube feet all over the body, often longer and more visible as dense lateral or posterior-ventral patches. Elongated (but damaged and distorted) specimen from NMV F308202 is ~ 110 mm long, 15 mm wide and 15 mm high, while others are closer to an oval or spindle shape once preserved (e.g. 34 mm long, 12 mm wide and 12 mm high: NMV F308237, preserved). Body wall contains many quadri-radiate table ossicles made of a perforated base disc with elevated central primary cross and four tall vertical spires, joined in two places, and angled out to four (rarely three) spinous arms at the tips. Table dimensions up to ~120 μm across by 104 μm high ( NMV F308237). Base discs typically irregular with a central ring of approximately eight large irregularly rectangular perforations, often with a secondary outer ring of eight or more smaller round to triangular perforations, though this is variable.

Remarks. Within Mesothuria the dense covering of tube feet is reminiscent of Mesothuria murrayi , but these specimens are distinguished by taller, more elegant ossicle tables, with long slender spires (joined in two places) and spinous ends.Along with the original description in Heding (1940), morphological identifications were made using the additional images and keys from Gebruk et al. (2012) and notes and personal correspondence from O’Loughlin (2018). While these specimens represent a major geographic range extension for the species (see below), O’Loughlin (pers comm., 2018) also placed the species off eastern Australia at abyssal depths, with his specimens displaying table ossicles with 3–5 spires, but similar dimension to IOT specimens at 80–120 μm high, with a diameter of up to 128 μm across the table disc. The type specimen ( Heding, 1940) had uniformly four spires, irregular or crooked at the apex, but our specimens were closer to those described by Gebruk et al. 2012, again with (typically) four spires, but more uniform at their spinous tips.

Distribution. Atlantic Ocean, Indian Ocean (Australian IOT), and off eastern Australia from Tasmania to Queensland.*

Full bathymetric range: 820–4930 m * (IOT 820–1991 m).

Type locality. East Atlantic (Gulf of Guinea area), 2278 m .

*Previous range from Gebruk et al. (2014) was limited to the Atlantic Ocean (various locations) with the depth from Rogacheva et al. (2013) at 1292–4930 m. While this species was not previously recorded from Australia in AFD or ALA (January 2024), the NMV catalogue has records from all eastern states, with specimens identified from off southern Tasmania to the Coral Sea in Queensland at depths of 1013–2650 m. These IOT specimens, along with other NMV catalogue records for Australia, represent a major geographic (and slight bathymetric) range extension for the species.

References. AFD (2024), ALA (2024), Gebruk et al. (2012), Gebruk et al. (2014), Heding (1940), O’Loughlin (notes and personal correspondence, 2018), Rogacheva et al. (2013).