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NEMERTINA, or NEMERTEANS (Nemerlea)

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Originally appearing in Volume V19, Page 364 of the 1911 Encyclopedia Britannica.
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NEMERTINA, or NEMERTEANS (Nemerlea) , a subdivision of See also:worms,' characterized by the ciliation of the skin, the presence of a retractile See also:proboscis, the See also:simple arrangement of the generative apparatus, and in certain cases by a See also:peculiar pelagic larval See also:stage to which the name " pilidium " has been given. Many of them are See also:long See also:thread-shaped or ribbon-shaped animals, more or less cylindrical in transverse See also:section. Even the comparatively shortest See also:species and genera can always be termed elongate, the broadest and shortest of all being the parasitic Malacobdella and the pelagic Pelagonemertes. There are no exterior appendages of any See also:kind. The See also:colours are often very See also:bright and varied. Nemertines live in the See also:sea, some being See also:common amongst the See also:corals and See also:algae, others hiding in the muddy or sandy bottom, and secreting gelatinous tubes which ensheath the See also:body along its whole length. Formerly, they were generally arranged amongst the Platyelminthes as a sub-See also:order in the order of the Turbellarians, but with the advance of our know-ledge of these See also:lower worms it has been found desirable to See also:separate them from the Turbellarians and to look upon the Nemertina as a separate phylum. O. See also:Burger classifies Nemertines into four orders: I. Protonemertini, in which there are two layers of dermal muscles, See also:external circular and See also:internal See also:longitudinal; the See also:nervous See also:system lies external to the circular muscles; the mouth lies behind the level of the See also:brain; the proboscis has no stylet; there is no caecum to the See also:intestine. Families, CARINELLIDAE, HUBRECHTIIDAE. II.

Mesonemertini, in which the nervous system has passed into the dermal muscles and lies amongst them; other characters as in Protonemertini. See also:

Family, CEPHALOTHRICIDAE. This order represents the Hoplonemertini of Hubrecht. IV. Heteronemertini, in which the dermal musculature is in three layers, an external longitudinal, a See also:middle circular, an internal longitudinal; the nervous system lies between the first and second of these layers; the See also:outer layer of longitudinal muscles is a new development; there is no intestinal caecum; no stylets on the proboscis and the mouth is behind the level of the brain. Families, EUPOLIIDAE, LINEIDAE. i Nemertes was a sea nymph, daughter of See also:Nereus and See also:Doris. One of the genera was named Nemertes by See also:Cuvier. The See also:Nematomorpha are nearly solid,—quite so at each end, From See also:Cambridge Natural See also:History, vol. ii., "Worms,"&c., by permission of See also:Macmillan & Co., Ltd. 2 This order represents the Schizonemertini of Hubrecht and the family Eupolidae. The first three orders, which have a See also:double See also:muscular layer, external circular and internal longitudinal, are sometimes grouped together as the DIMYARIA; the Heteronemertini, in which a third coat of longitudinal muscles arises outside the circular layer, are then placed in a second See also:branch, the TRIMYARIA. The following families and genera are represented on the See also:British coasts: CARINELLIDAE, Cannella; CEPHALOTHRICIDAE, Cephalothrix, Carinoma; EJNEMERTIDAE, Eunemertes; OTOTYPHLONEMERTIDAE, Ototyphlonemertes; AMPHIPORIDAE, Amphiporus, Drepanophorus; TETRASTEMMIDAE, Tetra stemma, Prosorhocmus; MALACOBDELLIDAE, Malacobdella; EUPOLIIDAE, Eupo ia, Valencinia, Oxypolia; LINEIDAE, Lineus, Euborlasia, Micrura, Cerebratulus, Micrella.

End of Article: NEMERTINA, or NEMERTEANS (Nemerlea)

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