Phylum Mollusca
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Fig: Apple snail (Pila)
Characteristics:- Mollusca is the second-largest animal phylum & includes snails, slugs, oysters, cuttlefish, octopuses, and many other familiar animals.
- Bilaterally symmetrical, triploblastic & coelomate animals.
- The body is covered by a calcareous shell and is unsegmented with a distinct head, muscular foot & visceral hump.
- Except for cephalopods, all mollusks have such as open circulatory system.
- Nitrogenous wastes are removed from the body by the nephridium.
- Fertilization is both external & internal, oviparous with indirect development.
- Embryo developed into a free-swimming larva called a trochophore.
- Examples: Pila (Apple snail), Pinctada (Pearl oyster), Sepia (Cuttlefish), Loligo (Squid), Octopus (Devilfish), Aplysia, Dentalium (Tusk shell), Chaetopleura (Chiton)
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