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Published: Friday, 02 June 2017
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"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
head, a dorsal visceral mass and ventral muscular foot. anterior 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
, gonads and kidneys. pericardium 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.
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