Author: Undescribed

Order: Sacoglossa  Family: Plakobranchidae

Maximum Size: 5 mm

Sightings: Sunshine Coast

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Elysia sp. 32 Undescribed

Two specimens of this species were found, and collected for examination, from the tidal flats at Golden Beach, Pumicestone Passage, Caloundra, Sunshine Coast, Qld, 19/09/2021. They were observed crawling across the surface of the substrate in very shallow water. Size: 3-5 mm

The most characteristic feature of this species is the long, thin and tapering rhinophores – extremely so, for an Elysia. The rhinophores are at least one third of the total body length. The eye spots are large conspicuous black spots situated at the base of, and posterior to, the rhinophore insertions. The body is formed into a medial ridge that starts between the rhinophores and runs posteriorly before disappearing into the folded parapodia. The parapodia commence a short distance posterior to the eye spots, gradually coming together to form an undulating join that continues for half the animal’s length before separating again and tapering away to leave a short section of tail that quickly tapers to a point. The foot is wider than the body. Anteriorly the foot forms blunt, slightly tentacular corners. The anterior of the head forms a “flap” that hangs down over the anterior of the foot between the aforementioned tentacular corners and is notched medially such that two distinct lobes are formed.

Colour is essentially green with numerous tiny red spots on the parapodia together with white spots. Larger white spots are present at the base of the parapodia and ventral surface of the foot, tail, anterior of the head and along the rhinophores. Three dark patches are evident on the head, one each side at the anterior base of the rhinophores and the third medially between the rhinophores. Additional dark patches are located each side of the body, beneath the eyes.

This species appears to use its long rhinophores in the same manner that an aeolid nudibranch uses it long oral tentacles – testing the substrate ahead and to the sides but it may also just be as a result of its frequent changes of direction and their drooping. It moves quickly across the substrate.

This undescribed species of Elysia has some resemblance to Elysia chilkensis Eliot, 1916, notably in regard to the extremely long and thin rhinophores. The original account, of a single specimen, lacks an illustration and is short on description. Kathe Jensen (Sea Slug Forum, 2006) suggests a specimen found in Hong Kong may be Elysia chilkensis and has posted an image on SSF. Elysia chilkensis was originally described from Lake Chilika on the west coast of India, Bay of Bengal. It is said to be a brackish lagoon of over a 1000 square kilometres, depending upon the season. Rudman comments: “… I suspect Eliot’s Elysia chilkensis is unidentifiable.”

The colouration and form is similar to Elysia coodgeensis however the relative length of the rhinophores, the well-developed anterior foot corners and the distinctively notched anterior of this  species are certainly different and characteristic features.

David A. Mullins – September, 2021

References:
– Eliot, C. N. E. (1916). Mollusca Nudibranchiata, Fauna of the Chilka Lake. Memoirs of the Indian Museum, 5: 375-380

– Rudman, W. B., (2003 June 10) Elysia chilkensis Eliot, 1916. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/elyschil and associated messages.