CUMACEANS: Cumacea

PHYSICAL CHARACTERISTICS

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.

GEOGRAPHIC RANGE

Cumaceans live around the world in oceans, seas, bays, and estuaries to the deepest trenches.

HABITAT

Most species live in the ocean and brackish waters, but some are found in habitats where water is fresh for at least short periods of time. Many live on the bottom, just below the surface in soft mud or sand. They prefer habitats where there is some water current, but little wave action. One group lives on algae growing on rocks and broken bits of coral.

DIET

Most cumaceans eat tiny particles of plants. These materials are broken down into bits by grinding them down with grains of sand in their mouth or by using their mandibles to scrape particles off larger pieces. One group has sharp mandibles, suggesting that they might prey on microscopic animals.

BEHAVIOR AND REPRODUCTION

Cumaceans spend most of their time in mud or sand. They need to stay close to the surface so they can move oxygen-carrying water over their gills. The first pair of maxillipeds is used to move water forward from the walking legs through the carapace toward the head. Some species leave the bottom and swim up into the water after dark.

WHO KNOWS?

So little is known about cumaceans that it is unlikely that anyone would know if any species were threatened or endangered. They are sometimes found in large numbers, but their distributions are patchy in both small areas and over large distances. Under these circumstances it is difficult to determine if a drop in population numbers or their absence is a result of some environmental disturbance, or simply part of a little-understood natural cycle.

Males and females are required for reproduction. In most species the males spend at least some of their time swimming in open water in search of a mate. In some species the males do not swim, but have special antennae that are used to grab the female's abdomen. They hang on to their mates with their antennae until they have mated. Females carry their eggs in a special brood pouch under the thorax until they hatch. The larvae (LAR-vee) do not live in open water like most other crustaceans. Instead, they live in the same places as the adults and molt, or shed their exoskeletons, until they reach adulthood. Once they reach adulthood, they stop molting.

CUMACEANS AND PEOPLE

Some species are an important food source for young fish, such as salmon and cod. These fishes are caught and sold as food for people.

CONSERVATION STATUS

No species of cumaceans are considered endangered or threatened.

NO COMMON NAME (Cyclaspis longicaudata): SPECIES ACCOUNT

Physical characteristics: The smooth carapace of Cyclaspis longicaudata is almost ball-shaped. The abdomen is very long and slender; males have five pairs of pleopods.

Geographic range: They live in the cold waters of the North Atlantic, from northern Norway to the northeastern United States.

Habitat: They live on the bottom in sandy mud at depths from 395 to 16,400 feet (120 to 5,000 meters).

Diet: Nothing is known about what they eat.

Behavior and reproduction: Nothing is known about their behavior or how they reproduce. The shape of their bodies suggests that they spend little time swimming, except possibly when the males are looking for a mate. Some populations reproduce year-round.

Cyclaspis longicaudata and people: This species does not directly impact people or their activities.

Conservation status: This species is not considered endangered or threatened. ∎

FOR MORE INFORMATION

Books:

Brusca, R. C., and G. J. Brusca. Invertebrates. Second edition. Sunderland, MA: Sinauer Associates, 2003.

Ruppert, E. E., and R. S. Fox. Seashore Animals of the Southeast. Columbia: University of South Carolina Press, 1988.

Periodicals:

Watling, L. "Revision of the Cumacean Family Leuconidae." Journal of Crustacean Biology 11 (1991): 56-82.

Web sites:

Lowry, J. K. Crustacea, the Higher Taxa: Description, Identification, and Information Retrieval. Version: 2 October 1999. http://www.crustacea.net/crustace/www/cumac.htm (accessed on February 18, 2005).

Welcome to the Cumacean Page.http://nature.umesci.maine.edu/cumacea.html (accessed on February 18, 2005).