Dardanus megistos . They are usually acquired indirectly by buying an anemone, but are some times sold separately. These crabs should have a host anemone to feel comfortable. Arrow crabs are very interesting animals which should be kept one to a tank, as they will continually fight. Also, Arrow crabs should not be kept with Coral Banded Shrimps as they will fight as well.
Hermit crabs are also interesting, and vary in color and size.
Most are passive, butsome will eat corals and other invertebrates. Crabs are generally omnivorous and readily accept the same foods as your fish. Like shrimp, crabs can only eat food which has made it to the bottom of the tank. Thus, ensure some food is in reach of your crabs. Sea Urchins and Starfishes Most sea urchins and Starfishes are suitable for beginners who have a few months experience.