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The Seashore

Sea Slugs


Within the gastropod class there is a particularly colourful group known as the Opisthobranch molluscs. It is a large group but one that students often miss on the shore due to the small sizes of many. It is also because sea slugs are usually limited to the lower shore or sub-littoral region. These truly marine gastropods usually have a reduced shell, often within the body, or have it missing completely. For example the sub-group name Nudibranchia means "naked gills" because they are completely uncovered due to the lack of shell. Although the name suggests a marine version of land slugs they are totally different. So, this section is a bit tricky! There are many species and rather than have a page for each we have chosen to introduce some of the more common or weird.

Grey Sea Slug (Aeolidia papillosa)

Grey Sea Slug (Aeolidia papillosa)

Grey sea slug spawning in rockpool

This beautiful sea slug is pale grey and grows up to 10 cms in length

The Grey Sea Slug feeds on sea anemones whose sting cells are left undigested but are absorbed in to its body. They are transported intact to the dorsal surface and there laid down to be used as a defence mechanism. When they spawn in the summer they produce spirals of ribbon containing more than 400,000 eggs

This is one of the most common of the sea slugs and can be found under stones and amongst seaweed in rock pools. Mainly lower shore and beyond. A widespread Atlantic species.

Acanthodoris pilosa

Acanthodoris pilosa

Around a centimetre in length. Lacks colour but body is covered in tiny hair-like extensions or pili (hence name). This is visible in the photo. There is no shell present. Predator.

Sea Lemon (Archidoris pseudoargus)

The Sea Lemon (Archidoris pseudoargus): A widespread sea slug that can grow to a large size (12 cm) and is encountered under stones of the lower, rocky shore. Feeds on sponges, particularly bread-crumb sponge. It is a hermaphrodite and produces long streams of pale ribbons of many thousands of eggs.

 

Doto spp

Doto spp

Often tiny individuals of up to a centimetre long. Pale with red spots. Up to 8 pairs of cerata can be present along the body (5 in the one above). There is no shell present. Feeds mainly on hydroids in the lower shore or below. It is common and widespread but easily overlooked. They are hermaphroditic and will breed at most times of the year and produce strings of many thousands of eggs that hatch after 16 days. It is beleived that they can live for up to 9 months.

Elysia viridis

Elysia viridis

Usually a centimetre or so in length but can be up to 4 cm. Primarily green with blue and other bright spots. No shell. Lives amongst seaweed on which it feeds, especially Cladophora and Codium. The chloroplasts remain in tact and get transported into the digestive gland where they continue to photosynthesise for months. They breed between May and October producing egg masses of thousands of eggs. These hatch and develop into veleger larvae within a few weeks.

Flabellina spp

Flabellina spp

 

Sordana sp

Sordana sp

See also Aplysia, the Sea Hare


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