Hydatina physis
(Linnaeus, 1758)

Superfamily: ACTEONOIDEA
Family: Hydatinidae


Found circum-globally in tropical waters both in the Indo-West Pacific and the Atlantic.


UPPER: Shelly Beach, Manly, Sydney, New South Wales. October 1984. Shell length 45mm. PHOTO: Bill Rudman.
LOWER: Egg mass. Long Reef, Sydney, New South Wales. (Photographer unknown).


Micromelo undata

The Hydatinidae are the most modified of a group of cephalaspids which show the gradual diminution in the importance of the shell as a protective organ. The least modified are the acteonids (Pupa, Acteon) with a heavily calcified shell and a small, usually uncoloured animal. In Hydatina and Micromelo the shell has become thin and the animal large and brightly coloured. The protective operculum has disappeared. Species of Hydatina are very specialised worm feeders, eating only cirratulinid polychaete worms.

• Rudman, W.B., 1972. The anatomy of the opisthobranch genus Hydatina and the functioning of the mantle cavity and alimentary canal. Zoological Journal of the Linnean Society, 51: 121-139.

Authorship details
Rudman, W.B., 1998 (December 18) Hydatina physis (Linnaeus, 1758). [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/hydaphys

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