Scalidophora: Kinorhyncha

Light microscopy image of unspecified kinorhynch. Photo © Alvaro Esteves Migotto via Encylopedia of Life, Creative Commons Attribution Non-Commercial Share Alike

The Kinorhyncha are a small phylum of tiny segmented pseudocoelomate marine invertebrates that live between mud or sand grains, feeding on organic matter or diatoms. Although most species are marine, some have been found sandy beaches and brackish estuaries, while others live on hydrozoans, bryozoans, or sponges. In the past they have been grouped with rotifers, but it is now known that the two phyla are only very distantly related (both being protostomes). The fact that kinorhynchs are now placed in the scalidophoran clade of Ecdysozoa shows that the old category of Pseudocoelomates is a polyphyletic one; the pseudocoelomate condition having evolved a number of times as a side effect of minaturisation. It is quite possible also that the ancestral ecdysozoan was segmented, and kinorhynchs, like tardigrades and arthropods, retain this primitive condition (lost in nematodes and priapulids). Kinorhynchs do not have a fossil record, although as the related Priapulida extend back to the Cambrian (and possibly the Loricifera as well) it is likely that they also have a long evolutionary history. MAK120416

Links: Mud Dragon (Kinorhyncha) - Encyclopedia of Life; Kinorhyncha - Wikipedia; Kinorhyncha - Tree of Life Web Project