Hydatina physis from sthn Queensland

January 21, 2009
From: Gary Cobb

Concerning message #16645:

Hi Bill and Everyone!
Here is another record from our backyard. This is Hydatina physis which has been found subtidally and intertidally here. I have also taken taxonomic photos of the shell, showing the gills. Also it's food source, the polychaete worm, Cirratulidae, Timarete sp.
On dives the animal is found at night. Intertidally it occurs during the day time hours!

Locality: Sunshine Coast, sthn Queensland, 15 m - intertidal, Queensland, Australia, Pacific Ocean, 08 August 2008, Subtidal and Intertidal. Length: max 60 mm. Photographer: Gary Cobb.

Cheers
Gary

gary@nudibranch.com.au

Cobb, G.C., 2009 (Jan 21) Hydatina physis from sthn Queensland. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22145

Dear Gary,

Thanks for these nice photos. In your photo of the shell we can see not only the gill [which I have marked g] but also the penis [p]. Hydatina is one of the few opisthobranchs which retains an external penis like this, almost all the others have an eversible penis which is usually hidden in an internal sac when not in use. In cephalaspideans this sac is usually on the right side of the head.  Interestingly, many marine snails have an external penis situated in much the same position as Hydatina.

Thanks also for the photo of its food worm. Have you actually seen it feeding? Why I ask is that when I first discovered the food of this species I was relying on stomach contents. Because of the extremely elongated oral tube I suggested that it must capture its prey by everting this long 'proboscis' down the burrow of the worm, or the crevices in which it lives. Valda Fraser's photos [#21498] showing an everted black tube certainly supported this hypothesis, but I have never witnessed Hydatina actually feeding, so I would be interested in an 'eyewitness' account if you have seen it in action.

  • 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.

Best wishes,
Bill Rudman

Rudman, W.B., 2009 (Jan 21). Comment on Hydatina physis from sthn Queensland by Gary Cobb. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22145

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