Nudibranch (Facelina auriculata) ©Alex Mustard/2020VISION


Scientific name: Nudibranchia
Nudibranchs, also known as sea slugs, are soft-bodied marine molluscs that lack external shells.

Species information


Length: Species vary in size from a few millimetres to several centimetres in length. The largest British species has been recorded at 20cm.

Conservation status


When to see

January to December


There are more than 100 species in UK seas, where they feed on seaweeds, sea mats, sponges, anemones and other nudibranchs. Some species are able to incorporate the stinging cells from their prey into their own bodies, providing protection from fish and other would-be predators.

How to identify

Nudibranchs come in many colours and forms, often with two horn-like tentacles or feathery gills.


Widespread around the UK.

Did you know?

Nudibranchs are hermaphrodites, which means they have both male and female reproductive organs.

How people can help

When rockpooling, be careful to leave everything as you found it - replace any rocks you turn over, put back any crabs or fish and ensure not to scrape anything off its rocky home. If you want to learn more about our rockpool life, Wildlife Trusts around the UK run rockpool safaris and offer Shoresearch training - teaching you to survey your local rocky shore. The data collected is then used to protect our coasts and seas through better management or through the designation of Marine Protected Areas. The Wildlife Trusts are working with sea users, scientists, politicians and local people towards a vision of 'Living Seas', where marine wildlife thrives. Do your bit for our Living Seas by supporting your local Wildlife Trust or checking out our Action Pages.