Editing Clam shrimp (section)

== Characteristics ==
Both valves of the shell are held together by a strong closing [[muscle]]. The animals react to danger by contracting the muscle, so that the valves close tightly and the crustacean, as if dead, lies motionlessly at the bottom of the pool.

In most species the head is [[anatomical terms of location#Dorsal and ventral|dorsoventrally]] compressed. The [[Sessility (zoology)|sessile]] [[compound eye]]s are close together and located on the forehead; in the genus ''Cyclestheria'' they are truly fused. In front of them is a simple [[Nauplius (larva)|naupliar]] eye. The first pair of [[antenna (biology)|antennae]] is reduced and unsegmented. The second pair of antennae, however, is long and biramous. Both branches are covered with numerous bristles. The crustaceans swim primarily by swooping the antennae. In the common genus ''Lynceus'', which can open its spherical valves wide, the [[thoracic]] legs move in an oar-like manner along with the antennae.

The number of segments constituting the thorax varies from 10 to 32, and the number of legs varies accordingly. They are similar in structure to the legs of [[tadpole shrimp]], and similarly, their size decreases from front to back. In females, the outer lobes of several middle legs are modified into long, upward-bending threadlike outgrowths, used to hold the eggs on the dorsal side of the body under the shell. However, the main functions of the thoracic legs are respiration and carrying food forward to the mouth. The gills are basically the outer lobes of all thoracic legs that are closest to the base of the leg. The legs are in constant movement, and the water between the valves of the [[carapace]] is quickly renewed. The body ends in a large [[chitin]]ised [[telson]], which is either [[Anatomical terms of location#Directional terms|laterally]] compressed and bears a pair of large hooks, or dorsoventrally compressed, with short hooks.