Mollusca:

Organization: Organ level

Symmetry: Bilateral

Coelom: present (coelomates)

Segmentation: Absent

Arrangement of embryonic layers: Triploblastic

Digestive system: Complete

Circulatory system: Present

Respiratory system: Present

Habitat: Aquatic

Sexuality: Dioecious (sexes are separate).

 Notochord: Absent

 Reproduction: Sexual (oviparous)

Fertilization: Indirect

Respiratory and excretory organ: Gills

Distinctive features:

• It is second largest phylum of animalia.
• They have a calcareous shell that covers the body externally and is un-segmented with a distinct head, muscular foot and visceral hump.
•  A soft and spongy layer of skin forms a mantle over the visceral hump.
•  The space between the hump and the mantle is called the mantle cavity in which feather like gills are present that perform both respiratory and excretory functions.
• The anterior head region has sensory tentacles.
• The mouth contains a file-like rasping organ for feeding, called Radula.