Question

Octopus belongs to class of
(A) Mollusca
(B) Pelecypoda
(C) Arthropods
(D) Cephalopods

Answer 1

Hint:-General features of octopus are triploblastic, bilaterally symmetrical, organ system level of organisation, body divided into distinct head, visceral hump, and muscular fold, presence of mantle-a layer of skin-this is the characteristics features of mollusc., complete digestive system,gills or lung present as respiratory structure, closed circulatory system, excretory organ is organ of bojanus,,presence of sensory tentacles.

Complete answer:
Mollusca is the phylum and from above mentioned features octopus belongs to this phylum. There are 6 classes of molluscs, based on shell and foot (1)monoplacophora-the flattened bilateral and oval body has some anelidian character for example some internal organ exhibit metameric segmentation.for example neopilina galathea.(2)polyplacophora:-they are all marine bilaterally symmetrical with elongated body having mouth and anus at opposite ends,example is chiton.(3)scaphopoda:-they are marine and burrow in mud and send they are bilaterally symmetrical with two tubular shell opening at both end. The foot is conical hand used for digging, example is dentalium.(4) gastropoda:-largest class of molluscs comprising limpet ,slugs,snail the characteristic features that distinguishes all gastropod from other malicious is torsion.
(5) pelecypoda:-no head tentacle eyes jaws and radula. Foot often hatchets and extends between the mental lobe. Mostly filter feeder .(6) cephalopods:-cephalopods contain the most specialised molluscs including squids, octopus cuttlefish and nautiloids the foot is located on the head modified in the form of an oral arm.

So correct answer is (D)

Note:- Calcareous shell over the body which is mainly for protection purpose and acts like an exoskeleton is absent in octopus.Among molluscs cephalopods have only a closed circulatory system.