|
In the shell of gastropod mollusks (a snail shell), the lip is the free margin of the peristome (synonym: peritreme) or aperture (the opening) of the gastropod shell. In dextral (right-handed) shells (most snail shells are right-handed), the right side or outer side of the aperture is known as the outer lip (''labrum''). The left side of the aperture is known as the inner lip or columellar lip (''labium'') if there is a pronounced lip there. In those species where there is no pronounced lip, the part of the body whorl that adjoins the aperture is known as the parietal wall. The outer lip is usually thin and sharp in immature shells, and in some adults (e.g. the land snails ''Helicella'' and ''Bulimulus''). However in some other land snails and in many marine species the outer lip is ''thickened'', or ''reflected'' (turned outwards). In some other marine species it is curled inwards (''inflected''), as in the cowries such as ''Cypraea''. It can also be expanded, as in ''Strombus''; it can have finger-like processes (''digitate'') or it can be fringed with spines (''foliated''), as in ''Murex''. The lip is called ''emarginate'' when it is incised or slit, as in ''Pleurotomaria''. It is described as ''effuse'' when the basal or anterior extremity is slightly produced, depressed or reflected, as in Thiara. When the lip is bent into an "s" curve it is called ''sinuous'', as is the case in the sigmoidal margin of''Janthina exigua''. Interiorly when the lip has teeth it is ''dentate'' as in ''Nerita''. When the teeth are rib-like it is described as ''plicate'' or ''lamellate''. When it has numerous large plications, nodules or teeth it is known as ''ringent'', as in ''Pythia''. The lip is called ''sulcate'', when it is grooved within. It is known as ''labiate'' or ''marginate'', when it is callously thickened near the margin. ==References== * George Washington Tryon, Structural and systematic conchology, 1882, p. 46 File:Neobernaya spadicea 001.jpg|Inflected lip of ''Neobernaya spadicea'' File:MurexPectenGlobal.jpg|Foliated (fringed with spines) lip of ''Murex pecten'' File:Mikadotrochus hirasei 01.jpg|Slit lip of ''Mikadotrochus hirasei'' File:Thiara winteri 002.jpg|Depressed lip of ''Thiara winteri'' File:Nerita peloronta face.JPG|Dentate lip of ''Nerita peloronta'' File:Pythia scarabaeus shell.jpg|Ringent lip of ''Pythia scarabaeus'' 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「Lip (gastropod)」の詳細全文を読む スポンサード リンク
|