Sea Slug questions

February 12, 1999
From: Dale Kyd

Dear Dr. Rudman,
Thank you for replying so quickly, my son (7 years) would truly love to ask you some questions and they follow:

What is the biggest sea slug?
What do sea slugs eat?
What ocean do sea slug live in ?
Dale Kyd

Thank you for your time!
Beth Kyd

Kyd, D., 1999 (Feb 12) Sea Slug questions. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Dale,
Thanks for your questions.
What is the biggest sea slug?
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. The only photo of it I can find on the web is on Mike Miller's Slug Site. He has a photo of the nudibranch Tyrinna evelinae, and because it was named after Eveline Marcus, he has a photo below it on the same page with Eveline Marcus holding an Aplysia vaccaria in her hand. It doesn't seem to be a metre long though.

Have a look at the Sea Hare topics listed in the GENERAL TOPICS index for some background information on Sea Hares.

The biggest nudibranch, which are the most colourful Sea Slugs, is usually said to be 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.

What do sea slugs eat?
Sea Slugs eat a wide variety of foods. Some, such as the Sea Hares are herbivores, eating sea weeds. Others such as the nudibranchs are specialised carnivores, each species feeding on a particular food. If you look around the Sea Slug Forum you will find some photos of different Sea Slugs and their food. A few examples of nudibranchs feeding are:
Glaucus atlanticus which feeds on the floating cnidarian Physalia,
Gymnodoris subflava, which feeds on other nudibranchs,
Favorinus japonica, which feeds on other Sea Slug eggs, and
Jorunna sp., which is one of many dorid nudibranchs that feed on particular sponges.

What ocean do sea slug live in ?
Sea Slugs live in all oceans of the world. Each region has its own species, but some species can be found right across the tropical Indian and Pacific Oceans from East Africa to Hawaii, and from Japan to Australia. A few, like Hydatina physis are found all around the tropics, including the Pacific and Indian Oceans, the Carribean and mid Atlantic Islands. I am just putting some pictures on the Forum of species that are found only in Antarctic waters, which clearly shows that wherever there is sea water, you are likely to find Sea Slugs.

If you look at the other questions and answers on this page, (below yours), you will more information about Sea Slugs.

I hope this will help,
Best wishes,
Bill Rudman.

Rudman, W.B., 1999 (Feb 12). Comment on Sea Slug questions by Dale Kyd. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


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