“Crab, a common name for any of a group of crustaceans characterized by a reduced abdomen and enlarged and broadened anterior portion of the body.”1 Crabs are related to shrimp and lobster, which are also crustacean decapods. True crabs have a reduced abdomen, “like a folded up lobster,”which is tucked under the body forming a so called “abdominal flap.” This flap is one way to differentiate a male crab from a female, the male flap being triangular formed and female having instead an oval shaped flap.2
The abdomen is also not used in locomotion anymore, but instead can function as a pouch in the female for her eggs. The crab’s body has numerous sets of appendages having five sets of legs and two antennae. Crab’s pincers, also called chelae, are found on its front legs and are used for feeding, defense, and display. The crab’s body is covered in a shell, or carapace, functioning as its exoskeleton, consisting of chitin with a waxy finish.
Crabs also possess a rather complex nervous system, able to thrive in many different aquatic environments, ranging from marine to tropical waters. Their senses have also increased in complexity, having compound eyes and the sense of smell and taste, which are used in the finding food and potential mates. To end, crabs are unique in that they walk sideways, burrow, and swim, all through evolutionary developments.3