Re: Photo of a living 'Berthella' sideralis

January 8, 2007
From: Jussi Evertsen

Concerning message #19133:

Hi Bill,
I did identify Erling's specimen [message #19089] as a Berthella  based on material that I have myself of similar looking specimens, but with tissue covering the whole dorsum. I suspected Erling's specimen to be damaged. My ID is based on the descriptions given in Odhner  (1939). In my notes in my field notebook I noted the internal shell visible thorugh the dorsal tissue, and the gills located in a cavity on the sides between the dorsal tissue and the foot.

Here are the photos of the specimen of Berthella that I have from Rundholmen at Bud 20/5 2004, collected at 28 meters depth. The specimen is 20 mm from the head to the end of the tail.

Also I have scanned the illustrations given in Odhner (1939) with lateral illustrations of B. plumula and B. sideralis. I also scanned the shell of B. plumula. In Odhner (1939) it is mentioned that B. plumula has been collected from the the tidal zone. I do not agree that Erling's specimen  is a velutinid, but a damaged Berthella exposing the internal shell, because his specimen is similar to the above given specimens ID'd as Berthella from Odhners descriptions and illustrations.

Locality: Rundholmen, 28 m, Bud, Norwegian west coast, 20 May 2004, rocky bottom, steep slope. Length: 20 mm. Photographer: Petter Schmedling.

  • Odhner, N.H. (1939) Opisthobranchiate Mollusca from the western and northern coasts of Norway. Det Kongelige Norske Videnskabernes Selskabs Skrifter, 1: 1-93.


Evertsen, J., 2007 (Jan 8) Re: Photo of a living 'Berthella' sideralis. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Jussi,
Thanks for these photos. If I had had these with Erling's message I would not have considered to be a pleurobranch. It is clearly a velutinid. In Erling's photo the head tentacles are short and blunt and I was happy to interpret the eye spots as being in the body wall at the base of the tentacles as you might expect in a pleurobranch. Your photos clearly show the long tapering head tentacles and the eyes in little pockets on the base of the tentacle - both characters of what we used to call 'prosobranch' gastropods, but not found in opisthobranchs. More specifically in pleurobranchs, we would expect to find enrolled tentacles, as illustrated in Odhner's sketches, and can be seen in many photos on the Forum of species of Berthella.

Why I asked Erling if he had a photo of the right side of the animal was to see if I could see any sign of the gill which, as illustrated in Odhner's sketches, should be on the right side of the body under the mantle.  Your second photo shows the underside of the body from the left side, so we wouldn't see the gill if it was a pleurobranch. However it is very valuable because it shows a clear channel - above the head - leading down to a large hole [arrowed] behind the left eye. This hole is the inhalent opening into the mantle cavity, through which water enters the mantle cavity which contains the chemosensory osphradium, the gills, anus, kidney and reproductive openings. In velutinids the mantle cavity is situated above the head and anterior body and covered by the shell. In pleurobranchs, this mantle cavity is lost, all that remains of it is the region on the right side of the body where we find the gill, anus and reproductive openings.

You mention differences in shell exposure. In some velutinids the amount of shell visible is very variable because the mantle covering it is quite contractile, much like in many cowry snails. Unfortunately it seems we are yet to see a living Berthella sideralis. It puzzles me that all the preserved specimens of B. sideralis and its Nth American counterpart Gymnotoplax americanus (Verrill, 1885) have the shell greatly exposed, much as in Erling's photo. I have never seen that happen in preserved specimens of other species of Berthella, so perhaps Berthella sideralis does have an exposed shell when alive. The other alternative, that all specimens so far collected have suffered identical damage seems rather unlikely.

Best wishes,
Bill Rudman

Rudman, W.B., 2007 (Jan 8). Comment on Re: Photo of a living 'Berthella' sideralis by Jussi Evertsen. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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