Phylum Cnidaria: General Characteristics and Classification

Table of Contents

After reading this article you will learn about Phylum Cnidaria: General Characteristics and Classification.

Habit & Habitat

Coelenterates are also known as Cnidaria due to presence of stinging cells called Cnidoblast
Cnidarians composed of two layers of tissue known as ectoderm and endoderm with non cellular layer called mesogloea in between
Epidermis is made of muscular cells, cnidoblasts, sensory cells, nerve cells and germ cells
Gastrodermis is inner lining of the gastrovascular cavity. It is a single-layered tissue with gland cells
and phagocytic nutritive cells
Basic body shape of cnidarians consists of sac with gastrovascular cavity or coelenteron with a single opening
Tentacles are finger like structures which surrounds the mouth of coelentreates
Tentacles are used for food capture and defense
Cnidoblasts are stinging cells with a poison filled capsule called nematocyst
It contains a poisonous substance called hypnotoxin

Body Forms of Cnidaria

I) Polyp

II) Medusa

Reproduction in Cnidaria

Asexual by Budding
Sexual by production of gametes
Development is indirect
Alternation of generation:- Its also known as metagenesis. This phenomenon shown by some cnidarians in which polyps produce medusa asexually and medusa form the polyps sexually. E.g. Obelia

Class 1. Hydrozoa

Class 2. Scyphozoa

Class 3. Anthozoa

All polyps
No medusa stage
This class has two types of animals
1. Sea anemones:- Skeleton absent
2. Corals:- CaCO3 Skeleton

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