Grey sea slug

Grey sea slug

Devon Wildlife Trust

Grey sea slug

Scientific name: Aeolidia filomenae
This large ‘grey’ sea slug is anything but dull!

Species information


Up to 12cm long

When to see

April to October


This large species of ‘nudibranch’ sea slug feeds on a wide variety of sea anemones! They can lay up to 400,000 eggs on the underside of rock in a beautiful ribbon-like formation.

How to identify

This large sea slug usually has grey, brown or fawn colouration. It is covered in lots of floppy projections unique to nudibranchs, known as ‘cerata’. It also has a white V-shaped mark on the front of its head.


Common around the British Isles and Ireland, as well as colder northern waters of Europe

Did you know?

Not only is this sea slug able to eat sea anemones without getting stung, but it can actually reproduce the anemone’s stinging cells into its own body for protection!

How people can help

Always follow the Seashore Code when rockpooling, taking care where you walk and making sure you put animals and rocks back gently. The Wildlife Trusts are working with sea users, scientists, politicians and local people towards a vision of 'Living Seas', where marine wildlife thrives.