These are the true crabs, which possess flattened bodies, an abdomen located on their bottom side and short antennae. They are not fussy eaters, usually free from diseases, and mainly carnivorous.
Catching unwanted crabs is a question I've fielded numerous times. The best way to rid unwanted specimens comes with using a large tall glass, similar to a drinking water glass. Simply bait the glass with a tasty morsel and place the upright glass at the aquarium bottom touching some rock in the evening. The crab will sense the food and using the rock surface, gain entrance to the glass. Because the glass has smooth sides, it won't be able to climb out. Not always 100% effective, but has resolved some terrible crab problems.
These are called 'Shame-faced' crabs because they hold their large claws in front of their face. During the day they are hidden in sand and after nightfall, they come out to search for snails, their favorite meal. They rarely appear in the trade.
This spider-like crab is one of the more interesting crabs for use in marine aquariums. Since they are very aggressive towards each other, only a mated pair can be kept together. They should not be kept in any aquarium that contain feather dusters or tubeworms. Worm steak is always on their menu. I have even seen them snip off a piece of mushroom polyps. Otherwise, they appear to be fairly safe in the reef environment. They are also good small bristle worm consumers. Those seen in the trade usually hail from the Caribbean and the coast of Brazil, however the species is also found in the Eastern Atlantic and Pacific Oceans.
These 'sponge crabs' are furry bodied with large strong front claws. They carry portions of corals, barnacles, and other décor on their shell.
Even though this Phylum has nothing to do with crabs, there is one member that interests many marine hobbyists and that is the Horseshoe Crab. Actually, it's not a crab, as it is more closely related to scorpions and spiders. In fact, they have remained unchanged for 350 million years. It is mentioned here only because it is one of the better sand stirrers. Small juveniles, less than six inches (15 cm) are fine for aquariums containing a sandy bottom. Yet, beware, it can attain a size of about 2 feet (60 cm) in the wild. Safe for use in the reef aquarium.
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