Question

The most active animals in Mollusca are
A. Bivalvia
B. Gastropoda
C. Pelecypoda
D. Cephalopoda

Answer 1

Molluscs are the invertebrate animals. This is the largest phylum after Arthropoda. Based on their symmetry and other characteristics, this phylum is divided into 7 classes namely Aplacophora, Monoplacophora, Polyplacophora, Bivalvia , Gastropoda , Cephalopoda, and Scaphopoda. They also serve as an important source of food.

Complete answer:
Among the 7 classes, let us discuss the 4 classes given in the options. First coming to bivalves, as the name indicates these can be identified by the presence of two halved shells. Bivalvia was previously called Pelecypoda and Lamellibranchiata. The examples include oysters and mussels. Next coming to Gastropoda , these commonly include slugs and snails. These were previously called as univalves. This is the largest class and contains many diversified species. Pelecypods usually have two shells that protect the animal and include oysters, clams, mussels and bivalves. Cephalopods mainly include octopus, squid, nautilus etc. This class has the most complex brain among all other invertebrates. The most intelligent, active and mobile group of the molluscs is Cephalopoda.

Hence, the correct answer is option D

Note:
The word mollusca means soft bodied. This word has been derived from Latin word mollis which means soft. The body is soft which is in turn protected by a hard shell. Mollusks usually have no brain with the exception of cephalopods. These are economically associated with humans. They also play an important role in the marine ecosystem.