Question

Silicon Blasts occur in
A. Calcarea
B. Hexactinellida
C. Demospongia
D. Both A and B

Answer 1

Hint: Sclero blasts that produce siliceous spicules are known as silicon blasts. Sclero blasts are the cells which make the structural elements of the skeleton. Skeletal structures not only consist of spicules, but also contain spongin fibres.

Complete Answer:
- Spicules chemically formed from carbonates of lime or silica.
- Spongin fibres, another component of the skeleton, are composed of a silk-like scleroprotein.
- According to the composition of material spicules are of two types: Calcareous and Siliceous.
- Calcareous mainly contain calcium carbonate and which occurs in Calcareous and Siliceous mainly contain silica which occur in the class Hexactinellida.

So, the correct answer is silicon blasts occur in Hexactinellida.

Additional information:
- The spicules are released by scleroblasts also known as mesenchyme cells.
- Based on the size, spicules are classified into two types: Megascleres and Microscleres
- Megascleres are large-sized and constitute the main supporting framework.
- Microscleres are small and present the mesenchyme.

Note: Hexactinellida means having six rayed siliceous spicules. They have definite bodies, crystalline appearance and consist of simple spines radiating from a single point.