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Nuda
Nuda is a class of ctenophores or comb jellies. The class contains a single family, Beroidae, with two genera, ''Beroe'' and ''Neis'', and the group is more commonly referred to as the "beroids". They are distinguished from other comb jellies by the complete absence of tentacles, in both juvenile and adult stages. ''Beroe'' is found in all the world's oceans and seas, and the monotypic ''Neis'' occurs only near Australia; all beroids are free-swimmers that form part of the plankton.
==Anatomy==
Some members of the diverse genus ''Beroe'' may occasionally attain a length of up to , though most species and individuals are less than about 10 cm; ''Neis cordigera'' is among the largest species in the class, often exceeding in length. The body is melon or cone-shaped with a wide mouth and pharynx and a capacious gastrovascular cavity. Many meridional canals branch off this and form a network of diverticulae in the mesogloea. There are no tentacles but there are a row of branched papillae, forming a figure of eight around the aboral tip.
The sack-like body of the ''Beröe'' species may be cylindrical in cross section, or compressed to varying amounts according to species, while ''Neis'' is somewhat flattened and characterized by a pair of trailing gelatinous "wings" that extend beyond the aboral tip.
Like other comb jellies, the body wall of nudans consists of an outer epidermis and an inner gastrodermis, separated by a jelly-like mesoglea. The mesoglea has pigments that give many nudan species a slightly pink color; ''Neis cordigera'' may be yellowish or a deep orange-red.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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