Question

Which mollusca is called a tusk shell?
(A) Neopilina
(B) Pila
(C) Dentalium
(D) Doris

Answer 1

Hint:Mollusc is the second largest animal phylum which involves both terrestrial and aquatic animals. They possess organ-system level of organisation. Body of the molluscs is usually covered by a calcareous shell and it is unsegmented in nature. And hence, molluscs are also known as shell organisms.

Complete answer:
Phylum Mollusca is the second largest animal phylum. It consists of both aquatic and terrestrial animals, having an organ-system level of organisation. They are bilaterally symmetrical, triploblastic and possess true coelom. They are usually dioecious and oviparous in nature. Phylum Mollusca includes classes like Monoplacophora, Aplacaphora, Amphineura, Scaphopoda, Gastropoda, Pelecypoda, and Cephalopoda. Examples of Molluscs are as follows: Pinctada (Pearl oyster), Pila (Apple snail), Sepia (cuttlefish), Loligo (Squid), and Dentalium (Tusk shell).

Dentalium is also known as tusk shell. It belongs to the class Scaphopoda. It is found abundantly on seafloor sediment. The shell is tubular in shape and found to be open at both ends. It resembles elephant’s tusks in structure and hence, called tusk shell. It lacks eyes, gills and head. It is used in burrowing the sand. It respires through the mantle and excretes through nephridia. They are oviparous in nature and undergo indirect development through trochophore larvae.

Understanding the options one by one,
(A) Neopilina – It has a concave shaped and segmented shell. It belongs to the class Monoplacophora. Hence, this is not the correct answer.
(B) Pila – It is also known as apple snail. This is not the correct answer.
(C) Dentalium – It resembles elephant’s tusks in structure and hence it’s called tusk shell. This is the correct answer.
(D) Doris – These are shell-less organisms belonging to the class Gastropoda. This is not the correct answer.

Therefore, the correct answer is option (C).

Note:Majority of the molluscs possess calcareous shells. It is essential to remember both the common and scientific name of species. Since, Dentalium has elephant tusk shaped structure, they are also known as tusk shells. They are abundantly found on sea floor sediments and feed on microorganisms and detritus particles.