Mussels from around the British Isles.

The small specimen is the abundant Common Mussel, Mytilus edulis, at 52 mm long. This species is found in beds of millions all around the British Isles.
At Kingston beach, Shoreham-by-Sea, the Common Mussels attain a length of 70 mm, (a largish specimen measured 68 mm) but the above specimen at 52 mm is the normal size near low water mark.

The large specimen is the Horse Mussel or Clabachdubh (Black Mussel), Modiolus modiolus, at 142 mm long.

A bed of Horse Mussels (or Clabachdubh), Modiolus modiolus, at Noss Head off the northeastern tip of Scotland covers an area of 4 sq km.

Scottish Heritage News Report

Mussels feed by drawing water into the shell, filtering out the edible particles, and pumping the waste water out again through a different opening. If you look closely at a mussel with its shells partly open at the rounded end, you can see the two openings, one fringed to stop large fragments being drawn in, the other an oval hole. You have to approach carefully, or the mussels detect unusual water movement and shadows as you approach, and close the shell in case you are a predator looking for dinner!
                                                                                                                                                     by Jane Lilley

Dogwhelks feeding on a mussel.

Dogwhelks, Nucella lapillus, feeding on a Mussel, Mytilis edulis

Mussels and Dogwhelks

Pea Crab   Pinnotheres sp.

This crab, as its name suggests, has a shell the size of a pea. Or, at least the brown male Pea Crab has. This is the crab that can be seen swimming in estuaries over mussel beds. It the most active swimmer of all the British crabs.

The female is quite different. She is almost twice the size of the male and usually yellow with a bright red blob on its soft shell. She is hardly able to crawl and cannot swim.
Male (top) and female

She does not need to because she spends her whole life inside in a live mussel shell. The male fertilises her eggs by swimming inside the mussel when it opens to feed.

Mollusc Page

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