Explanation:
GENERAL CHARACTERISTICS OF CNIDARIANS
1)They are entirely aquatic, some in fresh water but mostly marine. *
2)Radial symmetry (can be cut into two equal halves by one plane passing through the center of the mouth) or biradial symmetry around a longitudinal axis with oral and anoral ends;no definite head.*
3)Two basic types of individuals : polyp which is sessile and attached,and reproduce asexually; Medusa-which is free swimming.
Polymorphism is a characteristics of many species, i.e,both polyp and medusa occur in same specie.*
4)Exoskeleton or endoskeleton is of chitinous, calcerous,or protein components in some.*
5)Body with two layers, epidermis(ectoderm) and gastrodermis (endoderm) with structureless mesoglea in between,so, they are diploblastic animals.*
6)They have special stinging cell organelles called nematocysts in either in either endodermis or gastrodermis or in both;nematocyst abundant on tentacles.*
7)An internal body cavity, the gastrovascular cavity, lined by gastrodermis and has a single opening, the mouth, which also serves as anus. No coelomic cavity, Extensible tentacles usually encirclethe mouth and are used for food capture.*
8)No excretory or circulatory system.*
9)Asexual reproduction by budding(in polyps) or sexual reproduction by gametes(in all medusa and some polyps); sexual forms are monoecious or dioecious; planula larva occurs. *
