The Class Gastropoda includes snails, slugs, limpets and sea hares - all animals referred to as 'gastropods.' Gastropods are mollusks, and a extremely diverse group that includes over 40,000 species. Envision a sea shell, and you're thinking about a gastropod, although this class contains many shell-less animals as well.
Characteristics of Gastropods:
- Many gastropods have one shell in which the animal can withdraw. The shell is usually coiled, and may be 'left-handed' or sinistral (spiraled counter-clockwise) or 'right-handed' or dextral (clockwise).
- Gastropods move using a muscular foot.
- All young (larval stage) gastropods undergo a process called torsion, in which the entire top of their body twists 180 degrees on their foot. This results in the placement of the gills and anus above the head. Gastropods have adapted in a variety of ways to avoid polluting their breathing water with their own wastes.
- Due to torsion, adult gastropods are asymmetrical in form.
- Kingdom: Animalia
- Phylum: Mollusca
- Class: Gastropoda
Such a diverse group of organisms has diverse feeding mechanisms. Some are herbivores, some carnivores. Most feed using a radula. The whelk, a type of gastropod, use their radula to drill a hole into the shell of other organisms for food.
Food is digested in the stomach. Because of the torsion process described earlier, the food enters the stomach through the posterior (back) end, and wastes leave through the anterior (front) end.
Depending on the species, gastropods may reproduce by releasing gametes into the water, or by transferring the male's sperm into the female, who uses it to fertilize her eggs.
Once eggs hatch, the gastropod is usually a planktonic larvae called a veliger, which may feed on plankton or not feed at all. Eventually, the veliger undergoes metamorphosis and forms a juvenile gastropod.