They range in size from about 1/4 to 8 in; the larger forms are commonly referred to as prawns.
Shrimps are predominately marine, but several families have invaded fresh or brackish waters, and one species that lives in mangrove swamps in South America is semiterrestrial. Most are bottom dwellers, some even burrowing into the sea bottom; others swim in the open sea.
Shrimps commonly feed on small animal or plant organisms, but some are scavengers. About 17 genera have light-producing units called photophores positioned around the body. Several genera form the basis of a major fishery, and some shrimps are commercially raised.
Shrimps generally have a laterally, or side-to-side, compressed body, which is divided into three parts: head, thorax, and abdomen. The head bears eyes on stalks and long antennae. Arising from the thorax are eight pairs of appendages: the first three pairs near the head are modified into mouthparts called maxillipeds; the remaining five pairs are the walking legs, or pereipods. The abdomen has five pairs of swimming legs, or pleopods, and one pair of uropods, which form part of the fanlike tail. The head and thorax are fused and covered by an overhanging shell called the carapace, which encloses the gills.
Shrimps swim by paddling with the pleopods of the abdomen and also by rapid and repeated bendings of the abdomen and tail. Food is generally caught by one or more of the walking legs and held to the mouth by the maxillipeds.
The suborder Natantia is divided into three sections: Penaeidea, Caridea, and Stenopodidea. The Penaeidea are characterized by the presence of small pincers (chelae) at the ends of the first three pairs of walking legs; the Caridea by pincers on only the first two pairs; and the Stenopodidea by pincers on three pairs, but with at least one leg of the third pair larger than those of the other two pairs.
