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    Kinorhyncha (Gr kinema motion + rhyncho snout) is a phylum of small (1 mm or less) marine pseudocoelomate invertebrates 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 eleven segments 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 are 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

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