Question

Give scientific reasons
Our body irritates if it comes in contact with jellyfish.

Answer 1

The phylum Cnidaria includes primitive multicellular animals, which are however more advanced than sponges. The old name of this phylum is Coelenterata. These are divided into 3 classes – Hydrozoa (hydra, obelia, etc.), Scyphozoa (Aurelia – the jellyfish), Anthozoa or Actinozoa (Adamsia, Astraea, etc.)

Complete answer:
To answer this question we have to discuss the class Scyphozoa. They are marine and solitary and are represented by bell or umbrella shaped medusae, which are without velum. Polyp form is reduced or absent. Example – Aurelia (the jellyfish).

Jellyfish occur in the coastal waters of the tropical and temperate seas. It floats passively or swims actively, singly or in shoal. It has a soft gelatinous saucer-like body. Its life cycle includes a free living planula larva and a fixed polyp-like scyphistoma larva. Jelly fish floats in cooler waters. The tentacles surround the mouth of jellyfish and possess cnidoblasts (stinging cells) which are used for offence and defence. When they are stimulated, they discharge to shoot out a long thread tube called nematocyst or stinging organ. The nematocysts (cnidoblast) may coil round the prey (called volvents), or attach to the prey (called glutinants) or inject a toxin called hypotoxic into the prey to paralyse it.

So, when our body comes in contact with jellyfish, our body feels irritation, due to Cnidoblast injecting the toxin in our body.

Note: The cnidarians have tissue level of organization, incomplete digestion tract surrounded by body wall, cnidoblasts for defence and offence, epitheliomuscular cells which play the role of epithelium and musculature, gonads (testes, ovaries) without gonoducts and network of nerve cells acting as ‘nervous system’.