September 25, 2003
From: Dave Behrens
Re mystery 'Triopha': I wouldn't swear to this but its a lot like Colga pacifica (Bergh, 1894). Martynov and Baranets just reviewed the genus. There is also a drawing in Just & Edmunds. Here are some photos by Roger Clark which were taken in the Aleutian Islands.
I shared these photos with Drs. Alexander Martynov and Olga Baranets at the Laboratory of Marine Research in Saint Petersburg, Russia who have been studying this genus and they confirmed the identification as C. pacifica. Both expressed excitement in seeing Roger's photos of this species because they had only seen preserved specimens from trawl samples and had never seen living material. Alexander replied to me - "All three specimens from the photos have the typical pattern of pre-branchial notal processes (very similar to Atlantic C. villosa , but the later species often has more rows on the back). A main row of elongate processes runs down the middle of notum and usually a pair of rows of similar processes accompanied it from the both sides. In some specimens these lateral rows are almost same length as the middle row."
The importance of Roger's photos is we can see the previously unpublished variation in color found in this species. Specimens vary from pure white with yellow gills and rhinophores shown above, and as described originally by Bergh, to specimens that are completely orange
I have written a fuller account for Mike Miller's Opisthobranch of the Week - week 354 .
• Martynov, A. V. & O. N. Baranets. 2002. A revision of the genus Colga Bergh (Opisthobranchia, Polyceridae), with description of a new species from the North Pacific. Ruthenica, 12(1): 23-43.
• Just H. & M. Edmunds. 1985. North Atlantic nudibranchs (Mollusca) seen by Henning Lemche. Ophelia, Supp. 2: 1-150.
Behrens, D., 2003 (Sep 25) Colga pacifica from the Aleutian Ids. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/10978
Thanks for sharing these photos. As you report on Mike Miller's site, we know almost nothing about living animals of this genus. I don't think Paul Simm's mystery is a species of Colga as there appear to be a quite orderly arrangement of compound tubercles down the edge of the mantle on each side, quite unlike the simple papillae found in Colga. While your message doesn't resolve Paul's little mystery, it is certainly nice to see photos of living Colga. I'm afraid drawings of preserved specimens, no matter how well executed, leave something to be desired.