Pleurobranchus testudinarius from Italy

September 19, 1999
From: Erwin Koehler

This photo was taken by Wolfgang Seifarth this summer in Italy on a nightdive.
If someone said it would come from the Pacific I'd say it is
Pleurobranchus forskalii. This species lives in the Mediterranean also, but I have no idea how it looks like there. Or is it Pleurobranchus
testudinarius = (Susania testudinaria)
? Or are both one species?

Koehler, E., 1999 (Sep 19) Pleurobranchus testudinarius from Italy. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

The photo is of Pleurobranchus testudinarius which is known only from the Mediterranean. There is a very similar species, Pleurobranchus mamillatus Quoy & Gaimard, 1832, in the Indo-west Pacific. It was described from Mauritius, and is known from South Africa, eastern Australia and New Caledonia. It has the same colour pattern as Pleurobranchus testudinarius, even down to the pinkish rings, but seems to have longer dorsal papillae than the Mediterranean species.

It is interesting that you suggest a similarity with the Indo-West Pacific species Pleurobranchus forskalii. The earliest name for Pleurobranchus testudinarius was a name which had never been used - Pleurobranchus forskahli delle Chiaje, 1822. Some years ago I asked the International Commission on Zoological Nomenclature to suppress that name as it would mean replacing Pleurobranchus testudinarius and would also be very confusing to have it and P. forskalii in use for quite different species, especially since P. forskalii seems to have recently made it into the Mediterranean through the Suez Canal.
Bill Rudman.

Rudman, W.B., 1999 (Sep 19). Comment on Pleurobranchus testudinarius from Italy by Erwin Koehler. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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