Question

Which one belongs to class Polyplacophora?
(a) Chiton
(b) Patella
(c) Pila
(d) Murex

Answer 1

Hint: Polyplacophora is a class of Phylum Mollusca whose members are mostly marine. This member of Polyplacophora is also known as the ‘coat of mail shell’ due to its characteristic exoskeleton that aids in curling or bending.

Complete step by step answer:
The phylum Mollusca includes soft-bodied animals who are mostly marine. Their body is unsegmented. It is morphologically divisible into a distinct head, muscular foot, and visceral hump. The visceral hump is enclosed in a glandular mantle that is covered by a shell.
Polyplacophora is a class of Mollusca which are characterized by a dorso- ventrally flattened and elongated oval body. In Polyplacophora, the shell is made up of many overlapping plates, counting up to eight in some. These arched plates interlock in a way so as to allow the animal to curl like a ball whenever it senses danger. E.g. Chiton.
- The other classes of Phylum Mollusca are Scaphopoda, Monoplacophora, Gastropoda, Pelecypoda, and Cephalopoda. They are differentiated based on the nature of the shell and foot.
- Scaphopoda is a marine mollusc whose shell is long, cylindrical, and open at both ends. The foot is adapted for burrowing and digging purposes. E.g. Dentalium.
- Monoplacophorans have a single large plate of shell and the foot is reduced. E.g. Neopilina.
- The shell of Gastropods is also made up of a single plate. The body is symmetrical in the early embryo. But during the stage of development, it twists and exhibits torsion, rendering the body asymmetrical. E.g. Patella, Pila, Murex.
- In Pelecypoda, the animals have a laterally compressed body. Their shells are made up of two halves with an unhinged anterior portion. Thus, they are also known as Bivalvia. E.g. Pinctada.
- In Cephalopoda, the head and foot region fuses and becomes indistinguishable from each other. The region bears eyes and eight tentacles.E.g Octopus.

So, the correct answer is ‘ Chiton.’

Note:
- In some members of Cephalopoda, the shell is absent. E.g Doris, Octopus. They are regarded as one of the most intelligent invertebrates.
- Pinctada is a sedentary oyster belonging to Pelecypoda. It is reared artificially to obtain the best- quality pearls. This method was introduced by Mikimoto of Japan.