These are
hermaphroditic and pigmentless crustaceans with an elongated and translucent body that measures in length. A heart is present, and their
exopods and pseudepipodites appears to be used for gas exchange. They have a large head, the hind edge of which covers the first
thoracic segment. The thorax consists of nine limb-bearing segments (thoracic limb VIII absent in Lightiella), followed by 10 limbless abdominal segments and a
telson. In the larva, all the trunk segments are ring-shaped, but more dorsoventrally flattened than in the adults. During growth the anterior segments turns into the thorax and the posterior segments which makes up the abdomen remains ring-shaped. No eyes have been observed in either the adult or larval stages, presumably because of their muddy natural habitat. The second pair of
antennae is located behind the mouth; in all other crustaceans the antennae are in front of the mouth at the adult stage, and only their larvae have antennae that have the same location as adult cephalocaridans. The mouth is located behind the large upper lip, flanked by
mandibles. The first pair of
maxillae is very small, and the second pair has the same structure as the following thoracic legs: a large basal part, equipped with outgrowths on the inner side, used in locomotion, a forked inner branch and two outer lobes - referred to as the "pseudoepipod" and the "exopod". The structural and functional similarity between the maxillae and the legs may be a sign of primitive organization; the maxillae are not specialized, as they are in other crustaceans. ==Ecology==