The Common Edible Crab, Cancer pagurus Linnaeus, is a familar enough sight with its pink oval-shaped shell with the pie-crust edging. However, if you take a really close look you will discover that the surface has a most interesting natural pattern and texture. It is covered with thousands and thousands of tiny white bumps or tubercles.
Sometimes the crab is further decorated by encrusting animals (known as epibionts) which attach themselves to the shells of both living and dead crabs – and lots of other seashore creatures and objects too. In the pictures just above and below you can see a crab in which the carapace is thickly covered with the white calcareous tubes occupied by the marine bristle worm Pomatoceros triqueter. The second crab that I spotted on the same day had very few tubes on its shell and the grainy surface is clearly visible.
Revision of a post first published 20 May 2010
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Jessica's Nature Blog 
What a marvelous close-up 🙂
I’ve found a great many crabs over the years but have yet to see one with tubercules on it. I see mostly rock crabs (Cancer irroratus) and green crabs (Carcinus maenas).
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I am not familiar with Cancer irroratus but the green shore crab does have tubercles on the shell, in the UK at least, but they are smaller and less regular than in Cancer pagurus ( see 11th picture for a close-up of the shell at https://natureinfocus.wordpress.com/2010/03/24/a-common-green-shore-crab-at-studland).
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