Question

True jelly fishes belongs to the class
A) Scyphozoa
B) Anthozoa
C) Hydrozoa
D) Both A and B

Answer 1

Hint: Jellyfishes belong to the phylum Cnidaria which is made up of four classes - Hydrozoa, Anthozoa, Scyphozoa and Cubozoa. Jelly fishes are free-living marine animals with an umbrella shaped body.

Complete answer:
True jellyfishes are invertebrates whose 90 % of the body is filled with water. There is no skeleton , hard parts or any organ system for specialized functions like respiration and excretion. They have a radial symmetry and also a gelatinous substance called mesoglea is found within their bodies.

Their life cycle is divided into two parts, namely a juvenile polyp form and an adult medusa form. Stinging cells called nematocysts form in the adult stage which cover the tentacles. Nematocysts help jellyfish to get hold of smaller fishes and keep their predators away. Tentacles are very long in them. All these characteristics are of marine class Scyphozoa of the phylum Cnidaria.

Option A: Scyphozoa is the correct option. A true jellyfish of Scyphozoa class has two layers the outer epidermis and the inner gastrodermis whereas the fake jellyfish is composed of many organisms called polyps. Fake jellyfish does not have 2 layers.

Thus, the correct answer is Option A) Scyphozoa.

Note:
i) Scyphozoan fishes are mainly found near the equator in tropical and subtropical areas waters like the Carribean Sea, The Atlantic oceans, etc.
ii) They are free-swimming and pelagic.
iii) Some of the true jellyfishes can sting the swimmers while some are harmless.
iv) The lifetime of a true jellyfish is only 3-6 months.
v) They move forward by contractions and relaxation of their muscles in the umbrella.