Re: Ancula gibbosa from Scotland

June 14, 2006
From: Jim Anderson

Concerning message #16821; #16863:

Dear Bill and Marina,
Thank you for the update and correction. I attach the 3 original jpegs
at the max resolution - perhaps these will assist.

By the way what are the significant ID characteristics between A. gibbosa and Polycera quadricolor? I don't think it is P. faeroensis

Regards,
Jim A

 

jander4454@gmail.com

Anderson, J., 2006 (Jun 14) Re: Ancula gibbosa from Scotland. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/16871

Dear Jim,
I only need to post your third photo, which you didn't send with your first message. Fortunately it solves the identity problem.

As to separating the three species. There are many internal anatomical differences between species of Ancula and species of Polycera, and fortunately there are a few external ones as well.  Firstly, in species of Polycera, there is an extension of the mantle edge into an 'oral veil' over the head, at the anterior end. The edge of this oral veil has a number of tentacular  processes which point out horizontally and are arranged in equal numbers on each side of the midline. Species of Polycera usually have a single lateral process alongside each gill, but this is not always a clear distinction, because related polycerids may have a number of processes alongside the gills.

In Ancula, their is no oral veil, there are two forward facing tentacular processes arising from the base of each rhinophore, and their are a number of lateral processes arranged on each side of the body, alongise and just behind the gills. Bernard Picton has sent in a nice photo [message #3910] of a yellow patterned example of Ancula gibbosa from Britain. The simplest difference from polycerids is the lack of an oral veil so the head is clearly visible from above.

In you two earlier photos the oral veil was not visible as the anterior end of the animal was facing down. Fortunately your photo here shows the oral veil quite clearly so we can be sure it is a Polycera. It is possible to distinguish P. quadrilineata from P. faeroensis, by using external characters but as both species are quite variable in colour, most of the colour pattern is not that useful. However the best distinction is that P. quadrilineata usually has 4 (rarely 6) oral veil processes, while P. faeroensis usually has 8 or more. As you animal has 4 long oral veil processes I am pretty sure it is P. quadrilineata.

Best wishes,
Bill Rudman

Rudman, W.B., 2006 (Jun 14). Comment on Re: Ancula gibbosa from Scotland by Jim Anderson. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/16871

Factsheet

Polycera quadrilineata

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