Lip (gastropod)
In the shell ofgastropodmollusks(a snail shell), thelipis the free margin of theperistome(synonym: peritreme) oraperture(the opening) of thegastropod 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 thebody whorlthat adjoins the aperture is known as theparietal wall.
The outer lip is usually thin and sharp in immature shells, and in some adults (e.g. the land snailsHelicellaandBulimulus). However, in some other land snails and in many marine species the outer lip isthickened(also calledcallused), orreflected(turned outwards). In some other marine species it is curled inwards (inflected), as in the cowries such asCypraea.It can also be expanded, as inStrombus;it can have finger-like processes (digitate) or it can be fringed with spines (foliated), as inMurex.
The lip is calledemarginatewhen it is incised or slit, as inPleurotomaria.It is described aseffusewhen the basal or anterior extremity is slightly produced, depressed or reflected, as inThiara.When the lip is bent into an "s" curve it is calledsinuous,as is the case in the sigmoidal margin ofJanthina exigua.
Interiorly when the lip has teeth it isdentateas inNerita.When the teeth are rib-like it is described asplicateorlamellate.When it has numerous large plications, nodules or teeth it is known asringent,as inPythia.The lip is calledsulcate,when it is grooved within. It is known aslabiateormarginate,when it is callously thickened near the margin.
References
[edit]- George Washington Tryon,Structural and systematic conchology, 1882, p. 46
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Inflected lip ofNeobernaya spadicea -
Foliated (fringed with spines) lip ofMurex pecten -
Slit lip ofMikadotrochus hirasei -
Depressed lip ofThiara winteri -
Ringent lip ofPythia scarabaeus
