Re: Polybranchia from the Canary Ids

March 23, 2001
From: Kathe R. Jensen

Dear Bill & Erwin,
The easiest way to distinguish Cyerce and Polybranchia is the presence of digestive gland tubules in the cerata of Polybranchia (absent in Cyerce). However, the specimen in the photo is so pale that it is not possible to see whether the yellowish colour of the central part of the cerata is due to faded digestive gland or not. Also, in Polybranchia the base of the cerata looks like it is "rolled in", forming like a stem of a flower petal.

Besides Polybranchia viridis, P. borgnini (Trinchese, 1896) has also been recorded from the Canary Islands (Ortea, 1981). According to this paper and to Thompson (1988) P. viridis has tuberculate cerata, whereas those of P. borgnini are smooth (I have only seen 1 specimen of P. viridis in Florida, and that was a long time ago). The reddish-brown pigment spots on the cerata occur in P. borgnini, but also in Cyerce cristallina (see Thompson, 1988).

• Ortea, J. (1981) Moluscos opistobranquios de las Islas Canarias. Primera parte: Ascoglosos. Boletim do Instituto Espana Oceanografico 6: 180-199.
• Thompson, T.E. (1988) Eastern Mediterranean Opisthobranchia: Oxynoidae, Polybranchiidae, Stiligeridae (Sacoglossa). Journal of Molluscan Studies, 54: 157-172.

Jensen, K.R., 2001 (Mar 23) Re: Polybranchia from the Canary Ids. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Kathe,
Unfortunately all the 'easy' ways of distinguishing the two genera don't work when the characters are not clear in the photo. I am hoping that someone with local knowledge will be able to recognise the species from the photo. I think I can see brownish-yellow branches of the digestive gland in the cerata, and small tubercles over the face of the cerata, like those around the ceratal edge, which would make it Polybranchia viridis.
Bill Rudman

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