The Masked Crab
This tiny critter – its shell about 5 cm long – was on Swansea beach on the mud at the low tide line. They are common but I’ve never seen one before because they reverse into the sand or mud leaving only the snorkel (see below) at the front poking out above the surface.
The name “masked crab” comes from the patterns on the carapace which resemble a human face, though in this case they are hidden under a layer of mud.
It hides away, buried in sandy substrates, feeding on invertebrates such as polychaete worms (bristle worms) and bivalve molluscs. It uses its two antennae to form a breathing tube that takes oxygenated water down into the substrate. The claws (chelipeds) of males are much longer than the body, while those of females are only about as long as the carapace. This specimen, therefore, is female.