Question

Sensory structure of a cnidoblast is
A. Cnidocil
B. Retractile rods
C. Myonemes
D. Operculum

Answer 1

These are mechano chemical receptors. These lie on the external surface of the organism. It resembles a hair like structure.

Complete answer:
Cnidocyte (also called cnidoblast or nematocysts). It is an explosive kind of cell. It contains a giant organelle known as a cnidocyst or a cnida. It delivers sting to other organisms. Cnida is a part of the self defence system for the organism. It captures prey and acts as a defense against the predators. This organism fires a toxin from within which lies in the cnidocyst. Cnida is a bulb shaped capsule. A coiled helical structure is attached to this capsule. When the organism is in its immature state it is called cnidoblast. On the external surface it has a hair like structure known as a cnidocil. It is a mechano and chemical receptor in nature. When activated, it ejects a tubular shaft which penetrates inside of the organism. This discharge takes place within milliseconds. After it penetrates the organism it captivates the immobilized prey for itself. Cnida are divided into various types—
Penetrant— It is the largest and the most complex type.
Glutinant— It contains a sticky surface which allows the prey to stick to its surface
Volvent— It is a small and pear shaped.

So, the correct answer to the above question is A i.e Cnidocil.

Note: Cnidoblast is also referred to as cnidocyst. It belongs to phylum cnidaria. These cells differentiate from a specialized form of stem cells which replaces throughout its life.