Crab ?

This is from a recent night dive offshore at about 45 feet. The critter is about a half inch wide and apparently has no bottom end. The claws were constantly clutching the water and every so often would take something to the mouth but I could not see what it had caught. With those arms as large as they are it seems a little odd in its proportions. Anyone have a name for it?

It is a Squat Lobster. No idea as far as a genus or species though.

p.s. You have posted enough that we know you do your diving in Japan, but it is still a good form to include the location in ID request posts.

Squat lobsters aren't lobsters at all. Did you notice they have only 3 pairs of legs in addition to the big first pair with claws? The abdominal region is folded under the thorax. These are a member of the infraorder Anomura along with hermit crabs and porcelain crabs.

I think there are far more unknown species than known species in terms of their living color. The one you photographed is similar to one called Galathea sp A in Kato & Okuno's fine book "Shrimps and Crabs of Hachijo Island"but I don't know if it's actually the same species.

There's a great series of Japanese invert photo guides published by Hankyu Communications Co./ TBS-Britannica Co. Dr. Okuno is co-author on the Hachijo book & on another for Kume Island, Okinawa. TI' sure you find them quite useful.