General characteristics of phylum Mollusca:

(i) They have a soft, bilaterally symmetrical body with little segmentation and without appendages. Body cavity is haemocoel.

(ii) Body is divisible into an anterior head, a ventral foot and a dorsal visceral mass. The entire body is covered by a thin fold of skin called mantle, which secretes a hard calcareous shell of one or more pieces.

(iii) Respiration occurs via gills, mantle or a "lung" of the mantle.

(iv) Sexes are usually separate.

Examples: Chiton and Pila.