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Neogastropoda is an unranked taxonomic clade of sea snails, marine gastropod mollusks. For many years up to 2005, Neogastropoda was considered an order. == Description == The available fossil record of Neogastropoda is relatively complete, and supports a widely accepted evolutionary scenario of an Early Cretaceous origin of the group followed by two rapid diversification rounds in the late Cretaceous and the Paleocene.〔 These sea snails only have one auricle, one kidney and one monopectinate gill, i.e. the gill filaments develop on only one side of the central axis. The shell has a well-developed siphonal canal. The elongated trunk-like siphon is an extensible tube, formed from a fold in the mantle. It is used to suck water into the mantle cavity. At the base of the siphon is the bipectinate (branching from a central axis) osphradium, a sensory receptacle and olfactory organ, that is more developed than the one in the Mesogastropoda. They achieved important morphological changes including e.g., the elongation of the siphonal canal, a shift in the mouth opening to a terminal position on the head, and the formation of a well-developed proboscis.〔 The nervous system is very concentrated. Many species have the ganglia in a compact space. The rachiglossate (rasp-like) radula, a layer of serially arranged teeth within the mouth, has only three denticles (small teeth) in each transverse row.〔 The Neogastropoda have separate sexes. There are about 16,000 species. Neogastropoda includes many well-known gastropods including the cone snails, conchs, mud snails, olive snails, oyster drills, tulip shells, and whelks. The Neogastropoda all live in the sea, except ''Clea'', a freshwater genus. The neogastropods are most diverse in tropical seas.〔 They are mostly predators, but some are saprophagous (scavengers). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Neogastropoda」の詳細全文を読む スポンサード リンク
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