What is the largest sea slug?

Dear Amelia,

Your question arrived at a very opportune moment. See Yoshi Hirano's message about his large find in Japan.

I think the biggest Sea Slug is a species of Sea Hare called Aplysia vaccaria which is found on the west coast of North America from Morro Bay, California to the Gulf of California. Dave Behrens, in his book Pacific Coast Nudibranchs says it can grow to about 1 metre long and can weigh nearly 14kg. I can't find a good photo of it on the web, so if someone would like to send me one I would like to put it on the Forum.

The biggest nudibranch, is usually said to be the tritoniid, Tochuina tetraquetra which is found in the north Pacific, from the Kuril Islands in Russia, south to Malibu, in Los Angeles County, California. A picture of it can also be found on Mike Miller's Slug Site. It can grow up to 300mm long.

However a large form of the dorid nudibranch Hexabranchus sanguineus is reported to grow to at least 520mm in length off Djibouti in the Red Sea (Double, 1992). I have also seen photos of very similarly sized animals from deepwater off Fiji.

Pleurobranchs can also grow quite large. In a message on the Forum I report finding animals of Pleurobranchus forskalii growing to 310mm in New Caledonia.

If anyone else has 'record' lengths, weights, etc let me know and I'll add them to this page.

Best wishes,
Bill Rudman.

Reference:
Double, T. (1992) Here be Giants. BBC Wildlife, 10(5): 34-40.