- "Aristotle" recognised many Cephalopods and Gastropods.
- In 1650 "Johnson" coined the word "Mollusca". "Linnaeus" included "Mollusca" in the phylum "Verms".
- In 1790 Cuvier laid the foundation for modern classification of Mollusca.
- In 1818 "de Blainville" proposed "Bivahlia" name.
- In 1821 "Gold fuss" proposed the name "Pelecypoda".
- In 1862 "Bronn" proposed the name "Scaphopoda".
- Finally in 1883 "Lankester" gave final position to Mollusca.
- Molluscs are soft bodied animals.
- These are distributed all over the world.
- About 90,000 species of Molluscs are known today.
- Molluscans are bilaterally symmetrical animals.
- They show soft, short bodies without segmentation.
- The body has an anterior head, a dorsal visceral mass and ventral muscular foot.
- Foot is modified for crawling, burrowing or swimming.
- The body is covered by a fleshy mantle which secretes a calcareous shell.
- The shell is usually external, or it may be internal, reduced or absent.
- The shell may be of one piece and called univalve or of two parts and known as bivalve.
- Between the mantle and the body is a mantle cavity into which the anus and kidneys open, and in which lie a pair of ciliated gills or ctenidia.
- The coelom is reduced to cavities of pericardium, gonads and kidneys.
- The main body cavity is a haemocoel.
- There is a dorsal heart with one or two auricles and a single ventricle.
- The respiratory pigment is haemocyanin.
- Sexes are usually separate, development is either direct or there is a modified trochophore called a veliger larva.
