Kinorhyncha (Gr. kinema motion + rhyncho snout) is a phylum of small (1 mm or less) marine pseudocoelomateinvertebrates that are widespread in mud or sand at all depths as part of the meiobenthos. They are sometimes called mud dragons.
They are segmented, with a body consisting of a head, neck, and a trunk of 11 segment. They do not have external cilia, but instead have a number of spines along the body, plus several circles of spines around the head, which they use for locomotion, withdrawing the head and pushing forward, then holding with the spines while drawing up the body. The spines are part of a cuticle secreted by the epidermis; this is molted several times while growing to adulthood. The head is completely retractable, and is covered by a set of neck plates called placids when retracted.
Kinorhynchs eat diatoms and whatever else they can find in the mud.
There two sexes that look alike, and the larvae are free-living, but little else is known of their reproductive process.
At one time, they were considered to be a class within a phylum Cephalorhyncha that included Loricifera and Priapulida, both are still considered the closest relatives to the kinorhynchs and constitute together the Scalidophora. Interestingly, since 2004 fossil worms named Markuelia have become known that seem to belong to the stemgroup of that taxon.
The two groups of Kinorhynchs are still generally characterized as orders rather than classes, about 150 species are known.
Order Cyclorhagida
Suborder Cyclorhagae
Family Echinoderidae
Family Zelinkaderidae
Family Centroderidae
Family Dracoderidae
Suborder Conchorhagae
Family Semnoderidae
Suborder Cryptorhagae
Family Cateriidae
Order Homalorhagida
Suborder Homalorhagae
Family Pycnophyidae
Family Neocentrophyidae
External link
Introduction to the Cephalorhyncha (http://www.ucmp.berkeley.edu/phyla/ecdysozoa/cephalorhyncha.html)
Drawings of Kinorhyncha (http://biodidac.bio.uottawa.ca/thumbnails/catquery.htm?maxrows_old=&StartRow=1&maxrows=8&kingdom=Animalia&phylum=Kinorhyncha)
Anteriograde movement is achieved by the eversion of the proboscis accompanied by the caudally-directed movements of the cephalic spines, which also serve as a holdfast.
These animals are incapable of escape swimming actions when threatened, so instead rely on retraction of the vulnerable head and erection of their defensive armoury of bristles for protection.
Kinorhyncha feed primarily on diatoms [Ruppert and Barnes, 1994], and other organic material that can be found in and above the sediment.
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