EVERYDAY SCIENCE

Detailed explanation-1: -Some gastropods have no shell at all, or only an internal shell or internal calcareous granules, and these species are often known as slugs. Semi-slugs are pulmonate slugs with a greatly reduced external shell which is in some cases partly covered by the mantle.

Detailed explanation-2: -Gastropods are characterized by the possession of a single (often coiled) shell, although this is lost in some slug groups, and a body that has undergone torsion so that the pallial cavity faces forwards.

Detailed explanation-3: -Those gastropods without a shell, and those with only a very reduced or internal shell, are usually known as slugs; those with a shell into which they can partly but not completely withdraw are termed semislugs.

Detailed explanation-4: -Gastropods have a muscular foot which is used for “creeping” locomotion in most species. In some, it is modified for swimming or burrowing. Most gastropods have a well-developed head that includes eyes, 1-2 pairs of tentacles, and a concentration of nervous tissue (ganglion).

Detailed explanation-5: -The majority (over 90%) of gastropod species have dextral (right-handed) shells, but a small minority of species and genera are virtually always sinistral (left-handed), and a very few species (for example Amphidromus perversus) show a mixture of dextral and sinistral individuals.