Cephalocarids: Cephalocarida

Cephalocarids (sef-fal-oh-KAR-ids) are small crustaceans, measuring 0.078 to 0.146 inches (2 to 3.7 millimeters) in length. The eyeless head is short, broad, and covered by a horseshoe-shaped shield. There are two pairs of antennae and two pairs of jaws. The first pair of antennae is not branched; it is uniramous (YU-neh-RAY-mus). The second pair is branched or biramous (BY-ray-mus). The second pair of jaws is also biramous. It is the maxillae (mack-SIH-lee), which follows the uniramous first pair of jaws and resembles the appendages on the rest of the body. Maxillipeds (mack-SIH-leh-pehds), fingerlike limbs associated with the mouth, are absent. The thorax, or midbody, has eight segments, each with a pair of paddlelike, biramous limbs. The abdomen or tail section has 11 segments with no limbs at all. The tip of the tail, or telson, has a pair of long, threadlike, uniramous appendages.