The Leptostraca includes just around 3 dozen species. Most are only 5 to 15 mm long, but Nebaliopsis typica may reach 5 cm. The body form of leptostracans is distinctive with a loose bivalved carapace covering the thorax, a protruding rostrum (or "snout"), and an elongate abdomen. All leptostracans are marine and most are epibenthic (living on the surface of the seabottom) from the intertidal zone (i.e., the zone that is exposed at low tide and submerged at high tide) to around 400 m (N. typica is bathypelagic, i.e., living in the zone between 1000 and 4000 m below the surface). Most species seem to occur in low-oxygen environments. One species, Dahlella caldariensis, is associated with the hydrothermal vents of the Galapagos and East Pacific Rise. Speonebalia cannoni is known only from marine caves. Most leptostracans suspension feed by stirring up bottom sediments. They can also grasp relatively large bits of food with their mandibles. Some are carnivorous scavengers and others are known to aggregate around areas of the sea floor where large amounts of detritus accumulate. In many species the antennae or antennules of males are modified to hold females during copulation.
(Brusca and Brusca 2003)