III.

Physical Description

Shrimp are crustaceans, animals with a hard shell called an exoskeleton that forms a head, thorax, and abdomen. In shrimp that live near the water’s surface, the exoskeleton is often transparent, making them less visible to predators. Bottom-dwelling shrimp are typically brown or green, while most deep-sea species are red. Shrimp that live in coral reefs can be quite vivid in color, and include some of the most beautifully colored animals in the seas.

Structurally, shrimp are similar to crabs and lobsters but have bodies flattened from side to side. The exoskeleton covering the shrimp’s head and thorax forms a rigid shield known as the carapace. The exoskeleton of the abdomen is flexible. The abdomen is packed with muscle, and it can flex rapidly to give the tail a powerful flick. The abdominal muscles form the white meat of shrimp, the tastiest part of the shrimp for humans.

Shrimp have two pairs of whiplike antennae that contain sensory organs for taste and touch, which help shrimp find food. Bottom-dwelling species are quickly attracted by the scent of dead remains. Many shrimp species also have bulging compound eyes that are made up of hundreds of lenses joined together. The eyes act as an early warning system against predators—shrimp react instantly if they see anything moving overhead. Deep-sea shrimp have light-producing organs, called photophores, that scientists believe may help identify mates in the dark depths of the sea.

Shrimp have a large number of specialized legs. Eight pairs of legs are located on the thorax. Three front pairs, called maxillipeds, are used for feeding, while the remaining five, called pereiopods, are used for clinging and for walking. The pereiopods can be long and delicate, and they are sometimes thinner than a human hair. The abdomen has five pairs of legs, called pleopods or swimmerets. These legs are short and rounded, and they are used for swimming. Pleopods can also be used for burrowing, and some females use their pleopods to carry eggs.