Question

The main function of nematoblast in coelenterate is
A. Locomotion
B. Offence and defence
C. Reproduction
D. Nutrition

Answer 1

Hint: Nematocysts are specialized stinging cells specific to Coelenterates. They are also called Cnidarians. Cells that produce nematocysts are called nematoblasts. Coelenterata lacks a specialized circulatory system. It relies instead on diffusion across the tissue layers.

Complete step by step answer:
Nematoblast is a Cnidoblast which is a developing cell. Cnidocyte is a completely mature cell. The main function is offence and defence but it also helps in locomotion and food capture. Nematoblasts of cnidoblasts are sensory in nature and they contain nematocyst apparatus. Nematocysts form a tentacle-like structure that helps them to capture planktonic prey.
(A) Locomotion takes place by smooth muscle fibres and tentacles. Some like coral and sea anemone remain fixed on the substratum. Respiratory, excretory and circulatory organs are absent.
(C) In the coelenterates, reproduction is done in many forms. Like all metazoa, they can reproduce sexually. The fertilized eggs produce larvae which differ anatomically and ecologically from the adult sexually reproducing stage.
(D) Coelenterates are carnivorous in nature with few exceptions such as corals. They maintain symbiotic relationships with other animals for food. Digestion is done both intracellular and extracellular. Coelenterates body form is radially symmetrical, diploblastic and does not have a coelom.
Hence, the correct answer is option B.

Note: Coelenterata is a term encompassing the animal phyla Cnidaria which includes coral animals, true jellies, sea anemones, sea pens and Ctenophora like comb jellies. They have very simple tissue organization with only two layers of cells which are external and internal. Its body structure has radial symmetry.