Animal Behavior

Behavioral Ecology

Why do so many round animals seem to show only simple behaviors?

Examples of “round” animals include members of the phylum Cnidaria (hydras, jellyfish, corals) and phylum Echinodermata (starfish, sea urchins, sand dollars). An animal with radial symmetry usually has a nerve net that only allows very simple types of behavior. Animals that are round are usually sessile (nonmoving). This is in contrast to animals that display bilateral symmetry, which have a distinct head/tail and in which the animals can be divided into different planes. Bilaterally symmetrical animals usually move in a specific direction. (For more about animal symmetry, see the chapter “Aquatic and Land Animal Diversity.”)


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