Cephalocarida

a subclass of small primitive crustaceans. The body is elongate, measuring as much as 3 mm in length. It consists of a head, a ten-segmented thorax with legs, and a nine-segmented legless abdomen. At the end of the body is a ramus with two long bristles. The legs are used for locomotion and respiration, as well as for directing food toward the mouth opening. There are two pairs of antennae on the head, small upper jaws, and two pairs of lower jaws, which are practically indistinguishable from the thoracic limbs. The animals lack eyes, a condition related to their burrowing way of life. The female lays eggs into an egg sac located on the last segment of the thorax. Nauplii are hatched from the eggs and become adults only after 18 molts.

The subclass Cephalocarida was discovered in 1957. Its first identified representative, Hutchinsoniella macracantha, was found on the Atlantic coast of the USA. Other species have been found on the eastern and western coasts of North America and near Japan. Three genera, embracing four silt-dwelling species, are known.