Kinorhyncha
| Kinorhynchs | |
|---|---|
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| Scientific classification | |
| Kingdom: | Animalia |
| Clade: | Scalidophora |
| Phylum: |
Kinorhyncha Reinhard, 1881 |
| Orders | |
Kinorhyncha (Ancient Greek: κινέω kīnéō "I move", ῥύγχος rhúnkhos "snout") is a phylum of small (1 mm or less) marine invertebrates that are widespread in mud or sand at all depths as part of the meiobenthos. They are also called mud dragons.
Kinorhynchs are segmented, limbless animals, with a body consisting of a head, neck, and a trunk of eleven segments. Unlike some similar invertebrates, they do not have external cilia, but instead have a number of spines along the body, plus up to seven circles of spines around the head. These spines are used for locomotion, withdrawing the head and pushing forward, then gripping the substrate with the spines while drawing up the body.
The body wall consists of a thin syncitial layer, which secretes a tough cuticle; this is molted several times while growing to adulthood. The spines are essentially moveable extensions of the body wall, and are hollow and covered by cuticle. The head is completely retractable, and is covered by a set of neck plates called placids when retracted.
Kinorhynchs eat either diatoms or organic material found in the mud, depending on species. The mouth is located in a conical structure at the apex of the head, and opens into a pharynx and then an oesophagus, both of which are lined by cuticle. Two pairs of salivary glands and one or more pairs of pancreatic glands connect to the oesophagus and presumably secrete digestive enzymes. Beyond the oesophagus lies a midgut that combines the functions of a stomach and intestine, and lacks a cuticle, enabling it to absorb nutrients. The short hind-gut is lined by cuticle, and empties into an anus at the posterior end of the trunk.
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