Molpadida Haeckel, 1896

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 : 251

Order Molpadida Haeckel, 1896

Diagnosis. (following O’Loughlin et al., 2015). “Tentacles 15, digitate; body stout, lacking tube feet, usually with an evident tail; anal papillae, tentacle ampullae and respiratory trees present; ossicles may include tables, cups, rods, perforated plates and modified anchors; phosphatic bodies often present.”

Remarks. The Molpadida are burrowing holothuroids lacking any tube feet and with a sausage-like body often tapered to a tail. Despite the absence of tube feet, Molpadida do not group with the Apodida, though their position within the Neoholothuriida remains uncertain ( Miller et al., 2017). Molpadida often bury themselves in mud or silt and are known from the subtidal zone down to abyssal depths ( Pawson et al., 2001). They are represented worldwide by three families, with only Caudinidae and Molpadiidae currently recorded for Australia. Only Molpadiidae was represented in IOT material, with two lots of Molpadia from two stations at 3839–4766 m.

Family Molpadiidae Müller, 1850

Diagnosis. (following O’Loughlin et al., 2015, after Pawson, 1977). “Tentacles claw shaped or with terminal digits and few small lateral digits. Tentacle ampullae long or reduced. Spicules derived from tri-radiate tables with three-pillared spire. Tail with tables with round to oblong disc or long fusiform rods. Phosphatic deposits often present.”

Remarks. Ossicles of some species will gradually transform into light orange or red phosphatic deposits ( Pawson et al., 2001). Genera and species within Molpadiidae are differentiated by type or combination of ossicles which include tri-radiate and fusiform tables, fusiform rods, racquets, anchor plates and anchors; and presence or absence of phosphatic deposits ( Rowe et al., 2017). Of the three currently accepted genera worldwide, Heteromolpadia and Molpadia have been previously recorded from Australia, with only Molpadia being widespread. We found one Molpadia OTU in the IOT material, Molpadia cf blakei (2 lots).