About 6 results for ‘Slug’
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Slug
Slug is a common name that is normally applied to any gastropod mollusc that lacks a shell, that has a very reduced shell, or has a small internal shell. (This is in contrast to the common name snail, applied to gastropods that have a coiled shell large enough that the soft parts of the animal can retract fully into it. ) Slugs belong to several different lineages which also include snails that have shells. The various families of land slugs are not very closely related, despite a superficial similarity in the overall body form. The shell-less condition has arisen many times independently during the evolutionary past, and thus the category "slug" is emphatically a polyphyletic one. As well as land slugs, there are also many marine slugs and even one freshwater slug genus, but the common name "slug" is most frequently applied to air-breathing land slugs, while the marine forms are usually known as sea slugs. Land gastropods with a shell that is not quite vestigial, but is too small to retract into (like many in the family Urocyclidae), are known as semislugs. Slugs, like all other gastropods, undergo torsion (a 180° twisting of the internal organs) during development. Internally, slug anatomy clearly shows the effects of this rotation, but externally the bodies of slugs appear rather symmetrical, except for the positioning of the pneumostome, which is on one side of the animal, normally the right hand side. The soft, slimy bodies of slugs are prone to desiccation, so land-living slugs are confined to moist environments and must retreat to damp hiding places when the weather is dry.
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