Noalda sp. from the Andaman Sea

February 19, 2010
From: Lawrence Neal

Dear Bill,

Here is what looks like a species of Noalda. This microscopic individual was spotted by eagle-eyed Pornsak Noiphan, my diving buddy, off the west coast of Thailand. The animal's shiny brown shell is visible through a dorsal slit in the shield. It's seems to be crawling on red filamentous algae growing on the surface of a rock. That's pretty much all the information I can offer on this one. Apologies for the poor photo quality.

Locality: Tablamu, 6 metres, Phangnga, Thailand, Andaman Sea, east Indian Ocean, 13 February 2010, Rocky shoreline. Length: About 3 mm. Photographer: Lawrence Neal.

All the best,


Neal, L., 2010 (Feb 19) Noalda sp. from the Andaman Sea. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Lawrence,

When I saw your photos, the yellow markings reminded me of some photos I had recently seen of Noalda exigua [see message #23262] which bear a remarkable similarity to your animal. The head of your animal looks more like that of a gastropterid and the shell is more enclosed in your specimen, but the similarities are striking. However until we know something of the anatomy of these animals I couldn't positively say the resemblance is more than co-incidental. It would not be the first time that we have been tricked by external similarities in unrelated primitive opisthobranchs. However, to keep it simple I will include it, as you suggest, as a species of Noalda. This is the second species I have tentatively included in this problematic genus [see Noalda sp. 1]

Thanks for a most interesting find.

Best wishes,
Bill Rudman

Rudman, W.B., 2010 (Feb 19). Comment on Noalda sp. from the Andaman Sea by Lawrence Neal. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Noalda sp. 2