Identity of Limapontia depressa.

November 20, 2009
From: Ian Smith

Concerning message #22781:

Dear Bill
As you suggested some reservations about the determination of my L. depressa specimens, here is some more detail.

My Orkney specimens [message #22743] were dissected by Tom Gascoigne, whom Kathe mentioned, and he confirmed my det..  I have hunted out my correspondence with him. He commented about them that "at X25 only the anus could be seen", so I am not surprised that I haven't found a completely convincing view of the renal pore.

However, my uncontested L. capitata has anus and renal pore clearly visible in the appropriate adjacent positions for that species, and I am sure my brown specimens from Menai do not have openings in the L. capitata position.

You mentioned difficulty in using photographs for det. of Limapontia spp. This certainly applies to black specimens, so I would suggest replacing the Orkney photo with the brown specimens on message #22763 as the primary image on the L. depressa factsheet , as they show much more detail (sub-terminal anus, lack of pale metapodium, green branched gut, absence of rhinophores or crest.)

The sub-terminal anus is sufficient alone to separate them from the other two Limapontia spp..

In J. Conch. 28: 360 (1975) Tom says " They (L. depressa) show two adaptations for life on land - a thick coat of mucus to prevent water-loss and a sub-terminal anus for the efficient removal of faecal matter. --- they could be called amphibious".

The glistening mucus can be seen on my image of the specimen on the algal mat. I took several photos of L. depressa on the mat, and this was selected as the clearest; on the others the mucus was so thick it obscured most detail of the animal.

I have examined the algal mat closely, and it contains cellular and non-cellular filaments. So the cellular pieces seen by Skip in the photo do not preclude Vaucheria (as Skip also said in his second message #22780).
I have noted some interesting details of the feeding of L. depressa, so thanks for pushing me to re-examine them. I'll save the details for another posting.

• Gascoigne, T. (1975). A Field Guide to the British Limapontiidae and Alderia modesta Loven. Journal of Conchology 28: 359-364.

Best wishes
Ian

ifsmith@bethere.co.uk

Ian F. Smith, 2009 (Nov 20) Identity of Limapontia depressa.. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22821

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