Question

Which one of the following has the spiral shell?
A) Octopus
B) Pila
C) Unio
D) All of the above

Answer 1

Most of the molluscs possess a hard covering on them in order to protect itself from its predator by secreting a calcium carbonate based coating called a Shell. Usually many of the molluscs contain shells , these shells come with different shape and size and for different reasons. Spiral shell bearing molluscs belong to the phylum Gastropods.

Complete answer:
Octopus being a larger member of molluscs, they tend to protect themselves from the predators using shells but they are not spiral in nature, they cover themselves on both sides by using the shells which are attached at one end and open at the other. Unions use a bivalve shell for their protection but they are different compared to that of octopus shell, unio shell has concentrated rings and these rings increase in their radius at the periphery, these rings are oval in nature not circular. Pila is a freshwater snail which is found in freshwater ponds and lakes, tanks and also in rice fields and other marshy areas. This member of gastropods have spirally coiled globular univalved shells protecting them, they can vary in size, these shells consist of calcium carbonate.

Additional information: These spirally coiled shells can be of two types based on the direction of their coiling, they are: Dextral if they are coiled at right handed direction and Sinistral if there is left handed coiling. The shell consists of different regions based on their nature, the shell forms elongated coil at their centre of axis in a spiral manner and each revolution or coil is known as Whorl. The tip of each shell is known as Apex, apix is formed by the first deposition of the individual's mantle and therefore considered as the first formed region of the shell.

Therefore , the correct answer is Option B.

Note: The penultimate whorl and other whorls are large as they consist of body enclosed , the last whorl has an opening called an operculum found at the posterior side of the organism or at its foot. There is an elliptical area which is called a boss at the inner surface of the operculum.