I ordered 3 emerald crabs from petwarehouse.com and 2 of them only had 1 arm. They seen to function ok w/just one. I don't see them very often. They must do all their work at night. They are kinda scary looking, but do a get job on my green algae.
I'v got three in my tank and have had them for awhile. One lost a arm a little over 4 months ago. Grew back pretty quick. I'v also had a banded coral do the same thing.
