The Wonders of the Sea

Level of Organization

Cnidaria are in the tissue level of organization.

Germ Layers

Cnidarians have 2 germ layers. They are diploblastic which means they have an ectoderm layer and an endoderm layer.


The body symmetry of cnidarians is radial, which means that no matter how many body segments they have, the two halves will be mirror images of each other.


Cephalization means the formation of a head and since cnidarians don't have a head then they don't have cephalization.

Body Cavity

Cnidarians don't have a body cavity because GVC is not a body cavity.


They don't have any segmentation because they don't exactly have a head or any other body cavities.

Digestive System

Cnidarians have a simple sac digestive system which also has a single opening.

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Circulatory System

Cnidarians lack a circulatory system because they don't need one. All the cells that they have are in contact with the water, which has the oxygen and nutrients that the animals need.

Respiratory System

Cnidarians don't have any respiratory organs, and both cell layers absorb oxygen from and expel carbon dioxide into the water.

Excretory System

Cnidarians don't have any excretory organs. Jellyfish use their mouth for waste expulsion. In corals, the waste is excreted through their skin.

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Nervous System

The cnidaria nervous system may have been the origin of the nervous system. Their nervous system consists of a nerve net, nerve plexuses, and nerve tracts. It also has neurons.


Cnidarians have both asexual and sexual reproduction. Jellyfish males release sprem and females release eggs into the water.


Cnidarians have Hydrostatic support which are muscles around a fluid filled mass and they can have internal rodsor spicules for support.

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