What is Kinorhyncha?
{{Taxobox | image = Kinorhyncha.png | image_width = 150px | name = Kinorhynchs | regnum = [[Animal]]ia | superphylum = [[Ecdysozoa]] | phylum = '''Kinorhyncha''' | phylum_authority = Reinhard, 1887 | subdivision_ranks = Orders | subdivision = Cyclorhagida<br/> Homalorhagida }} [[File:Echinoderes hwiizaa.jpg|thumb|180px|''Echinoderes hwiiza'']] '''Kinorhyncha''' <ref>Gr. κίνηω, ''kīneō'' 'move' + ρυνχος, ''rhynchos'' 'snout'</ref> is a [[phylum (biology)|phylum]] of small (1&nbsp;mm or less) [[Ocean|marine]] [[invertebrate]]s. They are widespread in [[mud]] or [[sand]] at all depths of the sea. They are sometimes called '''mud dragons'''. About 222 [[species]] are known. Kinorhynchs eat either [[diatom]]s or organic material found in the mud, depending on species. ==Anatomy== Kinorhynchans are segmented, limbless animals. Their body has a head, neck, and a trunk. The trunk has eleven segments. They do not have external [[cilia]], but have a number of spines along the body, and up to seven circles of spines around the head.<ref>Brusca, Richard C. & Brusca, Gary J. 2003. ''Invertebrates'', p347. ISBN 978-0-87893-097-5</ref> These spines are used for movement. They can pull back the head and push forward; then they can grip the substrate with the spines, and draw up the body. The body wall is a thin layer with a tough [[cuticle]]. It is moulted several times during growth. This layer is a [[syncytium]], with [[nuclei]], but no [[cell membrane]]s. The spines are hollow and covered by cuticle. The head is completely retractable, when is covered by a set of neck plates.<ref name=IZ>{{cite book |author= Barnes, Robert D. |year=1982 |title= Invertebrate zoology |publisher= Holt-Saunders|location= Philadelphia, PA|pages= 286–288|isbn= 0-03-056747-5}}</ref> The nervous system is a ventral nerve cord, with one [[ganglion]] in each segment, and an anterior nerve ring surrounding the pharynx. This is the common arrangement for invertebrates. Some species have simple [[ocellus|ocelli]] (eye-spots) on the head, and all sp