Kinorhyncha
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Cyclorhagida |
Kinorhyncha (Gr. kīneō 'move' + rhynchos '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 also 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.
Their closest relatives are thought to be the phyla Loricifera and Priapulida. Together they constitute the Scalidophora.
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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