As well as all the fascinating organisms reported in On the Beach, if you delve down among the seaweeds you may find some colourful and graceful creatures that you might be surprised to learn are called Sea Slugs. Scientifically they are known as nudibranch molluscs, the first word meaning ‘naked lung’ and referring to the external gills that are often visible towards the rear of the animal. The name ‘mollusc’ suggests they should have a shell but true nudibranchs don’t have one.
They are quite unlike terrestrial slugs in your garden and can be found not only in rock pools but also on soft substrates such as mud, but they are easiest to find when they are climbing on seaweed. The can be very small so if you lift up some seaweed (gently) and see a tiny blob of pale ‘something’, do dip this portion of the seaweed back into the sea water and wait to see if it begins moving around.
The accompanying photographs, all taken on the Western Isles, show a Jorunna tomentosa, often found over soft substrates on the east side of the islands, an Aegires punctilucens found for many years on an exposed west headland and a Polycera quadrilineata which is found in a wide variety of habitats, often in groups.