Nemertina
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| Ribbon worms | ||||||
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The phylum Nemertina (or Nemertea, occasionally Nemertini) contains the ribbon worms or proboscis worms, which are a group of unsegmented marine invertebrates. There are about 1200 species distributed among two orders: Anopla and Enopla.
Nemertine worms are distinguished by their possession of an evertible proboscis that, in many taxa, is armed with a poisonous stylet, which is used in the capture of prey. Ribbon worms are carnivorous, feeding mostly on small invertebrates. Most Nemertea live in shallow seas and coastal waters, with a few inhabiting freshwater or damp soil. They range in length from 1 mm to as much as 30 metres (100 feet) in the case of the bootlace worm, Lineus longissimus. Some texts quote lengths of up to 60 m, in which case, L. longissimus would be the longest animal alive (female blue whales reach about 34 m).
Although generally considered acoelomate (that is, without a coelom-filled body cavity), the anatomy of the proboscis includes a coelom cavity. An old name for the phylum, Rhynchocoela, records this fact. They also possess a circulatory system, which may use haemoglobin, and a closed intestine. Members of the phylum Nemertea have often been considered as degenerate flatworms, but their placement has been extensively revised in recent years, and they are now placed in the Lophotrochozoa, along with more advanced animals, such as molluscs and annelids.it:Nemertea ja:ヒモムシ nl:Nemertea sl:Nitkarji