by Leo Shapiro
Around 150 species of kinorhynchs have been described since this group was first discovered on the northern coast of France in 1841, nearly all of them less than 1 mm long.
They have been collected as far north as Greenland and as far south as Antarctica, as well as in the Black Sea. Most live in marine sand or mud from the intertidal zone to a depth of 5000 to 8,000 m, but some are known from algal mats or holdfasts, sandy beaches, and brackish estuaries and others have been found living on hydrozoans, bryozoans, or sponges.
The general morphology of kinorhynchs is fairly homogeneous. The body includes a head (which can be retracted into the anterior portion of the neck), with both anteriorly and posteriorly directed spines, and a trunk. The body is divided into 13 distinct “zonites” (the head and neck being formed by the first two zonites and the trunk by the remaining 11), which are viewed as true segments by many specialists. The anus is on the last segment and is usually flanked by strong lateral spines. Kinorhynchs apparently lack a coelom (distinct body cavity).
Like arthropods (and most or all other groups in the superclade Ecdysozoa), kinorhynchs periodically shed their chitinous cuticle as they grow, but apparently do not molt as adults…
(read more: Encyclopedia of Life)
photo: © Alvaro Esteves Migotto