Most cumaceans are smaller than 8 mm long. The largest grow up to 25mm long; these large species tend to inhabit cold or deep water. They have a prominent carapace (cephalothorax) which covers their head and usually 3 thoracic segments, for this reason they are also called hooded shrimp. Cumaceans have two pairs of antennae, the first pair used as sensors, the second, which is reduced in the female but large and complex in the male, is thought to play a role in finding mates. Thoracic segments under the carapace (usually 3) each have a pair of short legs modified for manipulating food. The other five thoracic segments each have a pair of biramous (forked) appendages that they use for walking and swimming. They have a long, flexible abdomen, made up of 6 segments, which can bend under the rest of the body to clean the cephalothorax. The last abdominal segment has two cleaning appendages (uropods), and some species have a thin tail (telson). The first five of the six abdominal segments may also have appendages for swimming (called pleopods), but only in males. Females do not have pleopods.
This body plan is strongly conserved making cumaceans readily recognizable. However, cumaceans also show considerable diversity among species. Carapace can vary in color and texture, some are ornamented with setae, ridges and spines. Body shape also varies; some species have abdomens the width of the carapace, others are very slender, some are flattened and resemble flatworms. Leg length and number and size of eyes are also variable.
(Brusca and Brusca 2003; Kozloff 1990)
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