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Kinorhyncha (Echinodera; phylum Aschelminthes) A class (regarded as a phylum by many authorities) of very small, tube-shaped worms in which the cuticle is divided into distinct segments (zonites) but there is no metameric segmentation; there is a total lack of cilia (unlike Rotifera and Gastrotricha). Most inhabit marine environments, and all adopt a benthic mode of life. There are about 100 known species.