I have had them for about 6 months... they are various sizes, we have several different shape/size shells for them. They were moulting and changing shells frequently. They were always running around the rocks and would be very active at feeding times.
They have fought on occasion but never resulted in any damage... usually one throws the other off the rock and then both run off and do something else. the only fish I have seen pick at them is the scooter and he is just trying to steal their shrimp pellet.
I believe they were tank raised but not 100% sure.
tank mates: porcelain crab, blood shrimp, 3 sexy shrimp, 2 clowns, 2 small gobies(blackray, tangaroa) and a scooter. we also have a hammer coral.
Typically they eat algae, shrimp pellets, brine shrimp and cyclopes.
I assume if the missing 2 have died, then they were eaten in entirety by something since i see no parts in the tank.
i have a rena xp3 filter, a bubble hose thing, 30G bowfront tank with 30lbs live rock and 3 inch med-fine sand.