Fun Facts:

• Cnidarians can form symbiotic relationships with zooxanthellae (type of algae). This relationship is mutually beneficial.

• Jellyfish are made up of about 95% water. 

• Some jellyfish are technically immortal! Some can regenerate their tissue and can even revert to their juvenile stage.

• Cnidarians existed before dinosaurs, existing over 500 million years ago.

• The smallest animals in the world called Myxozoans are in this phylum. They are only 0.0085 millimeters, for reference a piece of paper is between 0.05 and 0.10 millimeters.

Key Characteristics:

• Body: have tissue but no organs. Respiration takes place via diffusion.

• Body forms: often times Cnidarians alternate between body forms during their lifecycle.

  • • • Polyp: sessile (non-moving), stalk-shaped.

      • Medusa: free-swimming, bell-shaped.

• Stinging Cells: have cnidocytes (stinging cells) for defense and to capture prey. The cnidocytes contain organelles called nematocysts (stingers).

• Digestive system: have only one opening that serves as both the mouth and anus (incomplete digestive system).

• Reproduction: can reproduce both sexually and asexually

• Symmetry: radial

Cnidarians Explained!