of their‘ walking’ legs( two out of four pairs) are adapted and used for holding onto their sponge cover rather than for propulsion, that is no surprise.
My search in the scientific literature indicates sponge crabs go to extraordinary lengths to create and retain their cover. A paper from 1926, for example, details the way a sponge crab would go about carving out a suitable piece of sponge from the encrusting growth on a large stone, or cut a larger piece of sponge down to size. The same observers also found that crabs preferred sponge to any other material but, if deprived of sponge, would systematically tear a piece of paper to make a covering of the right size and shape.
One conundrum is why sponge crabs, despite seeming to prioritise camouflage and being drab in colour otherwise, have such bright pink tips to their claws. I reckon it might make sense if the pink‘ nail varnish’ was used for some sort of signal to fellow crabs, as the claws can easily be held out
The unusual sight of a sponge crab on the move, clinging onto its‘ hat’ with its two rearmost pairs of legs
It took me a long time to realise there was a crab‘ wearing’ this sponge. How many others do we swim past?
for display when desired, or hidden beneath the crab’ s body when it needs to remain‘ incognito’.
While there may be an element of divers now having greater awareness of these unusual creatures and so noticing them more, it seems to be generally agreed that numbers are on the increase, around Plymouth, elsewhere in the Southwest and even further afield. The species has a generally southern distribution and is at the northern limit of its range here, so we might well get to see more as our seas become warmer. �
Paul’ s photos and video clips capturing UK marine life stories are on Instagram @ paulnaylormarinephoto
Sponge crab sitting in a sponge‘ garden’, its typical habitat, in Plymouth Sound
Crab with an orange‘ hat’ nicely matching its surroundings
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