Amazing proboscis on Hydatina physis from Sth Africa

April 8, 2008
From: Valda Fraser


Dear Bill
I've often seen Hydatina physis, but never this proboscis. Amazing! What is it for?

Locality: Mpande, 15 cm, Eastern Cape, South Africa, Indian, 15 March 2008, intertidal pool. Length: 40 mm. Photographer: Valda Fraser.

Regards
Valda

valdafraser@mweb.co.za

Fraser, V.J., 2008 (Apr 8) Amazing proboscis on Hydatina physis from Sth Africa. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/21498

Dear Valda,
Thanks for these interesting photos. I have never seen Hydatina with its proboscis [= oral tube] extendedlike this but when I studied these animals 30 years ago I did find on dissection that they had a very long muscular oral tube. Some specimens also had remains of cirratulinid worms in their gut. Cirratulinid worms live in crevices or in sand burrows and feed by extending long sticky tentacles out over the nearby sand and rock to pick up detrital food particles. I suggested that during feeding, the long oral tube was extended out of the mouth so that the jaws and teeth on the end of it could be inserted into crevices and burrows to grasp these worms. There are large muscles attached to the oral tube which would then drag it back into the body. Your photos show that the oral tube does indeed extend some distance outside the mouth. I suspect it can extend at least twice as long again as in your upper photo.

Species of Micromelo, and some species of Bullina [B. lineata does, B. roseana doesn't] have a long oral tube like this. In 1972, I had no information on the feeding choice of Micromelo and Bullina but since then I have discovered cirratulinid worms, or parts of them, in the alimetary canal of both Micromelo undata and Bullina lineata.

  • 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.
  • Rudman, W.B., 1972. Studies on the primitive opisthobranch genera Bullina Ferussac and Micromelo Pilsbry. Zoological Journal of the Linnean Society, 51: 105-119.

Best wishes,
Bill Rudman

Rudman, W.B., 2008 (Apr 8). Comment on Amazing proboscis on Hydatina physis from Sth Africa by Valda Fraser. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/21498

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