Question

Spicules occur in
(A) Annelida
(B) Mollusca
(C) Porifera
(D) Platyhelminthes

Answer 1

Hint: The spicules provide the structural support to the animals and they act as the defense mechanism when the predators attack them. These spicules vary in size. The large spicules are called megascleres and the small spicules are microscleres.

Complete Answer:
(A) Annelida:
The segmented worms are placed under the phylum Annelida. They have a soft body and do not possess any spicules of thrones. Example of this type is earthworm.

(B) Mollusca:
These are soft and the bilaterally symmetrical body. They have the calcium carbonate shell surrounding its body.

(C) Porifera:
Spicules are the structures that are present especially in the skeletal structures of the sponges. These are made up of calcium carbonate and are calcareous in nature. They are chalky in nature. Some spicules in the sponges consist of the layers of silicon and hence they are siliceous in nature. The sponges belong to the phylum Porifera. And hence the spicules occur in the porifera.

(D) Platyhelminthes:
The flat worms belonged to this category. The body is triploblastic and bilaterally symmetrical in nature and does not possess any thorns.

Thus, the option (C) is correct.

Note: The spicules in the sponges under the class Hexactinellida are made up of silica and the spicules in the sponges belonged to the class Calcarea is made up of calcium carbonate. They are calcareous and hence the class they belong to is called calcarea.