Cumaceans: Cumacea

Cumaceans (koo-MAY-see-ans) are strange-looking crustaceans with a large shieldlike carapace and slender abdomen. Their bodies resemble a comma lying on its side. Most cumaceans measure 0.039 to 0.39 inches (1 to 10 millimeters) long, but one species reaches 1.57 inches (40 millimeters). The head may or may not have a beaklike projection, or rostrum. In some species there is one compound eye on the middle of the head. Others have two compound eyes or no eyes at all. Each compound eye has multiple lenses and is not set on a stalk. The first pair of antennae, or antennules, is either branched (biramous), or not (uniramous). The second pair of antennae is uniramous. The mandibles, or jawlike structures, are uniramous and are usually used for grinding food.

The carapace covers the head and extends back over the first three of the eight thoracic segments. A sharp, beaklike extension of the carapace projects forward over the head. The first three segments are tightly joined, or fused, to the head. The first two pairs of thoracic limbs or maxillipeds (mack-SIH-leh-pehds) work with the mouth to handle food, while the third pair is leglike and used for walking. In females, the second pair of maxillipeds has special plates on their bases to hold eggs. The remaining pairs of thoracic limbs are called pereopods (PAIR-ee-oh-pawds). Depending on species, they are either uniramous (YU-neh-RAY-mus) or biramous (BY-ray-mus) and are used for walking.

The segmented abdomen is distinct and slender. The number of pairs of abdominal appendages, or pleopods (PLEE-oh-pawds), ranges from 0 to 5. In males the pleopods are fully developed, reduced in size, or absent. With the exception of one species, pleopods are not found on females. The tip of the abdomen has a pair of slender, well-developed appendages called uropods (YUR-oh-pawds). The uropods are biramous. In between the uropods is a single, long, tail segment, or telson.