Nemertea is a phylum of invertebrate animals also known as ribbon worms or proboscis worms. Most of the 1,400 or so species are marine, with a few living in fresh water and a small number of terrestrial forms; they are found in all marine habits, and throughout the world's oceans. Nemerteans are named after Nemertes, one of the
Nemertean worms are long, thin, unsegmented animals. They have no true head, although the anterior end is often slightly wider than the body. They are distinguished by the presence of an eversible proboscis which is used for catching prey. Although generally considered acoelomate, the cavity which contains the proboscis includes a true coelom.The body surface is ciliated, which may be the primary source of propulsion for the smaller species. Larger nemerteans use muscular peristalsis to crawl or swim.
Respiration is entirely by diffusion.
The receptor of the nemertine worms have a similar structure, but has a rootlet the function of which is not known, Moreover, the rhabdomere are not found to bear or originate from cilia.
Nemerteans range in size from 5 millimetres to over 30 metres long in the case of the European Lineus longissimus, with most species being 20 centimetres or less. There are also reports of specimens up to 50 m or 60 m long, which would make it the longest animal in the world; the longest vertebrate on record is a female blue whale, 29.9 m long
| Wikipedia, the free encyclopedia