That, my friend, is a staghorn hermit crab. The care level on these guys is considered difficult and must be added to a reef tank with caution.
The Staghorn Hermit Crab lives in a branching shell that is covered with hydroids and bryozoans. The crab itself is a hardy companion for the aquarium, but the shell that it resides in requires specialized care. This shell has multiple branches that resemble the branching SPS coral Acropora. Because of its shell, this crab may not be able to right itself if it were to fall on its back, and will be stung and damaged by corals and anemones in the reef aquarium.
Staghorn hermits are best kept in a biotope system with other filter feeding invertebrates, or in a refugium where the hydroids and bryozoans on its shell can be fed properly with types of live or prepared plankton foods. The biotope system or refugium is an ideal location due to the fact the shell must not come in contact with stinging corals and anemones. The crab itself will graze on algae, and if there is an insufficient supply to eat, supplement the diet with offerings of dried seaweed.
