Question

The shell of Nautilus is
a) Bivalved
b) Spirally coiled
c) Multi chambered
d) Both B and C

Answer 1

Nautilus belongs to the genus of cephalopods in the family Nautilidae. Cephalopods are the largest group of class Mollusca. They are the most ancient cephalopods belonging to the sub class Nautilidae.

Complete answer:
Molluscs are the second largest phylum and largest marine phylum. They are found in freshwater as well as marine water. But Cephalopods are mainly found in marine environments. Bivalve molluscs can be used as bioindicators for freshwater and marine water environments. They possess osphradia to test the chemical nature of water and statocyst help in maintaining the equilibrium. The body is usually covered by a calcareous shell. Their shell can be internal or external or not present at all. Here in the case of Nautilus the shell can be spirally coiled or multi chambered. The only modern cephalopod to have an external shell is Nautilus. The main function of the Nautilus shell is to provide protection to the organism as well as it provides enclosure of a system that helps Nautilus to control buoyancy.
Bivalve shell is part of the body, the exoskeleton or shell, of a bivalve mollusc.

So, the correct answer is Option D) i.e. Spirally coiled and Multi chambered.

Note:
The study of Mollusc is called Malacology. Cephalopods are of considerable economic importance to humans. Many species of squid and octopus are eaten. Nautilus shells are often used for decorative purposes, and the internal shell of a cuttlefish, or cuttlebone, is sold in the pet trade as a calcium source for birds. Octopus has eight arms and no shells. They contain ink glans for protection.
Molluscs are classified into Aplacophora, Monoplacophora, Polyplacophora, Gastropoda, Scaphopoda, Pelecypoda, Cephalopoda.