Kinorhyncha (kĭnˌərĭngˈkə) [key], phylum containing about 150 species of tiny pseudocoelomate worms, it is widely distributed in marine sediments. The kinorhynch body is divided into 13 segments, each covered with a cuticle and equipped with characteristic spines. The first segment is a bristly head that can be protruded or withdrawn. Using its head as an anchor, the creature burrows through the mud, pulling its body after it. Kinorhynchs have a relatively complex digestive system, a protonephridial (excretory) system, and a relatively simple reproductive system; no cloaca is formed. Sexes are separate, and the young hatch with 11 segments and add two segments posteriorly during their six-stage juvenile growth. They feed on microscopic algae and bacteria in the sediment. Very little is known of their ecological importance.