The nine described species of cephalocarids are benthic (on the sea floor) marine animals. They are found from the intertidal zone to depths of 1500 m. Cephalocarids feed on detritus (dead organic material) and are found in all kinds of sediment, from soft, silty mud to clean course sand.
The tiny (2-3.7 mm longthat's about the size of a sesame seed) body of a cephalocarid is elongate and fairly simple compared to most crustaceans. Most specialists think of them as rather primitive even though they have not yet been found in the fossil record. They consist of a head, a thorax with 8 segments that possess biramous, paddle-like appendages, an abdomen that consists of eleven segments with no appendages, and a telson. They lack eyes.
Hessler, R. R. 1984. Cephalocarida: living fossil without a fossil record. In: N. Eldredge and S. M. Stanley. eds. Living Fossils. Springer Verlag, New York. 181-186.