Author: Brown, 1979

Order: Cephalaspidea  Family: Colpodaspididae

Maximum Size: 5 mm

Sightings: Sunshine Coast

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Colpodaspis thompsoni G. H. Brown, 1979

Colpodaspis thompsoni is a snail-like headshield sea slug. It is small, only growing to a maximum of 3 mm in length. The globose body is black or dark brown with large patches of vivid white that contain one or more raised yellow circular pustules giving that classic fried egg appearance. It possesses a fragile bubble-shaped shell that is wholly internal being completely covered by the mantle. (There are a couple of members of this genus however that have an opening in the mantle that allows the shell to show through.) The black head tentacles are joined at their bases forming a vee shape. They are greyish on the outer edges and rolled into tubes each connecting with a deep groove laterally. There is a distinctive exhalent siphon on the right side and the tail is long tapering and unadorned-black in colour. The sole of the foot is a semitranslucent dirty white to grey colour and has a deep midline longitudinal groove for the posterior half that is fed mucus from a large gland positioned at the halfway point of the sole. It is postulated that the sticky mucus it produces helps provide attachment to the substrate in current and surge.

They are hermaphrodites but due to the locations of the openings to the male and female sexual organs they cannot inseminate simultaneously like most of the nudibranchs, but rather adopt a head to tail position, the specimen acting as the male being behind. The penis is located on the right side of the head right along side the mouth. It is quite long having been observed entering the partner’s exhalent siphon to access the female pore inside the enclosed mantle cavity.

The spawn of Colpodaspis thompsoni consists of quite large capsules in a mass of jelly-like mucus without any particular shape.

This species has a very wide Indo-Pacific distribution from the Red Sea and the African east coast right across to Hawaii, up to Japan and down to the central east coast of New South Wales, Australia.

Until recently Colpodaspis had been placed within the family Diaphanidae, mostly for the sake of convenience, but molecular sequencing in 2015 has shown sufficient difference, and confirming previous thoughts, to warrant it being in its own family – the Colpodaspididae.

References:
– Brown, G.H. (1979) An investigation of the anatomy of Colpodaspis pusilla (Mollusca: Opisthobranchia) and a description of a new species of Colpodaspis from Tanzanian coastal waters. Journal of Zoology, London, 187: 201-221.

– Rudman, W.B., 2006 (Nov 3). Comment on Colpodaspis thompsoni laying eggs by Ayumi Murakami. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/18191

– Rudman, W.B., 2008 (Jul 15). Comment on Colpodaspis thompsoni mating by Ayumi Murakami. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/21701

– Oskars TR, Bouchet P, Malaquias (2015). A new phylogeny of the Cephalaspidea (Gastropoda: Heterobranchia) based on expanded taxon sampling and gene markers. Molecular Phylogenetics and Evolution 89: 130–150.

– This Species Profile has been modified from a previously published article in Dive Log Magazine’s – Critter ID with NudiNotes Column, Issue: #371 (May 2019): 12 by David A. Mullins

David A. Mullins, July 2019