This is a tough shot to critique, because in many ways it's excellent. The subject itself is an appealingly jolly kind of crab - I had no idea that Sally Lightfoot crabs were so colourful, and you've brought the colours out beautifully without making them seem cartoonish. The focus is rightly on the front of the crab's shell, but the depth of field is sufficient to retain detail on the claws the the first three sets of legs too, whilst blurring the foreground and the background to avoid distracting the viewer.
Despite all of these positive aspects, however, I feel that this image doesn't quite match up to some of your others. Having thought about it for a while, I think the problem I have with this shot is that the crab basically sits in isolation. It's not part of a story, and it's not possible to tell what it was up to when you caught it so well.
Of course, it's possible that the crab was just sitting there and that there isn't really a 'story' to tell as such. And the absence doesn't mean that the shot doesn't work in a number of other contexts - it would be an excellent illustrative shot in an encyclopedia entry about the Sally Lightfoot crab, for instance. I just don't feel it's quite as compelling a wildlife shot as some of your other work once the viewer has got over the initial 'wow' factor of the technicolour crab and the technical expertise of the shot.