Crustacea (Crustaceans)

Abstract The Crustacea is a subphylum of arthropods defined by the nauplius larva, two pairs of antennae and biramous (‘two branched’) second antennae. Other limbs are biramous as well, and the body includes an abdomen, a thorax and a five‐segmented head. Mandibles and other specialised feeding appendages are present. The gut is lined with a cuticle that is molted along with the exoskeleton. A haemocoel and a dorsal, ostiate heart are present. Nephridial excretory organs may be specialised as antennal or maxillary glands. Crustaceans exhibit an incredible diversity and abundance, ranging from tiny planktonic or interstitial forms less than a millimetre in length to much larger forms, including shrimp, lobsters and crabs. An abundant fossil record is found, extending back to the Burgess Shale. Crustacean phylogeny has recently been roiled by the ‘pancrustacean hypothesis’: insects and crustaceans form one large clade. As traditionally viewed, crustaceans are thus very likely paraphyletic. Key Concepts: Crustaceans share several derived features: the nauplius larva, two pairs of antennae and biramous (‘two branched’) second antennae. Crustaceans exhibit an abdomen, a thorax and a five‐segmented head. Crustaceans have mandibles and other specialised feeding appendages. Molting is necessary for crustacean growth and includes the cuticle‐lined gut. Excretory organs may be specialised as antennal or maxillary glands. Crustaceans exhibit an incredible diversity and abundance. Crustaceans range from tiny planktonic or interstitial forms less than a millimetre in length to much larger and often commercially valuable forms such as shrimp, lobsters and crabs. The crustacean fossil record extends back to the Burgess Shale. Crustaceans and insects form one large clade, the pancrustaceans. As traditionally viewed, crustaceans are paraphyletic.