Looking more like aliens from a science fiction movie, these creatures are actually small crustaceans known as arrow crabs. Arrow crabs are quite common on the reefs of the Florida Keys and the Gulf of Mexico, where they scavenge for craps and dead fish. Their long legs can grow to 4 inches (10 centimeters) in length. Coloration is variable in this species. The body may be gold, yellow, or cream, marked with brown, black or iridescent-blue lines. Arrow crabs are popular with reef aquarium hobbyists because of their unique appearance.