Emerging largely un-noticed from the wet sand at low tide level at Rhossili Bay, Gower Peninsula, this small crab seems to be pushing up at least its own weight in sand.
Rinsed off in some standing water on the shore, you can see a few more details which allows me to suggest it is Pennant’s Swimming Crab, Portumnus latipes (Pennant).
This crab lives on the sand at low tide level and in the sublittoral up to a depth of 150m. It frequently buries itself in the wet sand to a depth of a couple of centimetres – as this individual had done to protect itself when the tide was out.
The crab in the two pictures below didn’t survive its burial in the sand; perhaps trodden on by one of the many surfers who use this stretch of the beach. However, its demise makes it possible to demonstrate the diagnostic features of the species more clearly.
The carapace is about 2 cm long and it is slightly elongate and heart-shaped, reddish with white mottling. Between the eyes there are three blunt ‘teeth’ of which the central one is a bit longer. The front claws of chelipeds are more or less the same size and are usually held under the carapace. The back legs end with a flattened leaf-shaped or spear-shaped segment or pereopod that acts like a paddle to help it swim.
You can find more information about Pennant’s Swimming Crab and other British crabs on the Glaucus web site.
Revision of a post first published 13 May 2009
COPYRIGHT JESSICA WINDER 2011
All Rights Reserved
Jessica's Nature Blog 
Hello Jessica, I’ve never noticed these crabs before, but I’ve seen similar on the beaches of Thailand.
At low tide they come out of burrows and are noticeable by the all the little balls of sand around the burrow.
When someone walks by they dart back down the burrow, coming out again a few seconds later.
Are you aware of these?
LikeLike
Hello, Ray. Quite a lot of crabs burrow in the sand. On a trip to Queensland in Australia a few years ago I saw several types of crab that burrowed, including the kind that you refer to. I haven’t written a post specifically about the species but there is a photo of the Sand Bubbler Crab on Kewarra Beach. Other crabs with similar habits for which there are postings are the Ghost Crab and the Soldier Crabs.
LikeLike