Thuridilla bayeri? found in tank

February 14, 2004
From: Marc

I found this little guy in my tank a few days ago. At first he was just hanging out on my back glass, and not moving at all, and now he is moving all over the live rock. My tank is a 20 Gallon High, the Live Rock is Tonga Deep water rock, and there is a 1.5" sand bottom in the tank.

Just curious what htis guy is, and wanted to make sure that he's okay for the tank, thanks for your help.

Marc, 2004 (Feb 14) Thuridilla bayeri? found in tank. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Mark,
I assume that if it is on Tonga Live Rock then the rock came from Tonga? Your animal is a species of Thuridilla. I am not sure of the species as there is some confusion, at least in my mind, as to just how many species there are. Your animal looks quite like what has been called Thuridilla bayeri, with the blue? spots along the parapodia and the white band on the rhinophores. However if you look at the other photos on this page there seems to be a range of pattern between this and Thuridilla gracilis. I guess we will have to wait until more material is available.

Is it for your tank. Species of Thuridilla are herbivores. I presume it is growing in your tank so I guess its finding thinks to eat. Perhaps it can survive on the green algae covering your live rock. It certainly shouldn't harm other occupants in your aquarum.
Best wishes
Bill Rudman

Rudman, W.B., 2004 (Feb 14). Comment on Thuridilla bayeri? found in tank by Marc. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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