Cells specialized even more than sponges and tissues (groups of similar cells) began with the cnidarians family. Nerves and muscles first appear in these animals, although they had no brain. Their behavior is very simple, responding automatically to touch. Nerves can carry more information between cells than hormones can. Nerves are the main feature which makes animals different from plants. Cnidarians might have evolved into flatworms.
Cnidarians might have appeared 650 million years ago. They belong to the group of animals called Cnidaria or Coelenterata. This group includes corals, hydras, jellyfish, Portuguese men-of-war, sea anemones, sea pens, sea whips, and sea fans.
Cnidarians might have appeared 650 million years ago. They belong to the group of animals called Cnidaria or Coelenterata. This group includes corals, hydras, jellyfish, Portuguese men-of-war, sea anemones, sea pens, sea whips, and sea fans.
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