Final answer:
Gastropods have a variety of shell shapes due to torsion during development, which affects their bilateral symmetry and results in asymmetrical bodies. Their shells are primarily composed of calcium carbonate and may be planospiral or conispiral. Gastropods use a radula for feeding and have a foot adapted for crawling.
Step-by-step explanation:
Class Gastropoda, which includes creatures like snails and slugs, exhibits a diversity of shell shapes and forms. These marine, freshwater, and terrestrial organisms have a single-valved shell primarily made of calcium carbonate. One defining characteristic of gastropod development is torsion, where the body rotates, causing the loss of bilateral symmetry and resulting in asymmetrical body shapes.
Gastropods can feature various types of shells, such as planospiral and conispiral. Planospiral shells resemble a garden hose wound up, while conispiral shells are akin to spiral staircases. Some species, like cowries, have polished surfaces due to the mantle extending over the shell during secretion. Additionally, torsion plays a crucial role in bodily organization, affecting the positioning of internal organs and nerve cords.
The gastropod foot is adapted for crawling, and most feature a head with tentacles and eyes. They use a radula to feed, scraping food particles from surfaces. The mantle cavity of aquatic species contains gills, whereas in terrestrial gastropods, it functions as a respiratory structure similar to lungs.