Class Gastropoda

Body asymmetrical due to torsion of visceral mass.

Pulmonary aperture for gaseous exchange.

Head well developed, tentacles bearing eyes and chemosensitive tentacles.

Mantle usually secretes a single coiled shell with visible growth lines.

Large, flat foot used for creeping.

Feeds using rasping radula.

eg. Helix- Garden snail

Class Bivalvia

Bilaterally symmetrical body.

Poorly developed head without tentacles.

Shell secreted in two halves which covers the whole body.

Small, pointed foot used for burrowing.

Filter feeders, using modified ciliated gills.

eg. Mytilus- Mussel