Phylum Mollusca - NEET-Biology

 Phylum Mollusca

Fig: Apple snail (Pila)

Characteristics:

• Mollusca is the second-largest animal phylum & includes snails, slugs, oysters, cuttlefish, octopuses, and many other familiar animals.

• Exhibit organ-system level of body organization.

• Bilaterally symmetrical, triploblastic & coelomate animals.

• The body is covered by a calcareous shell and is unsegmented with a distinct head, muscular foot & visceral hump.

• Most mollusks have a rasping tongue-like radula for feeding.

• Except for cephalopods, all mollusks have such as open circulatory system.

• Nitrogenous wastes are removed from the body by the nephridium.

• Mostly dioecious.

• 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)

Fig: Octopus (Devilfish)