MS-LS1.A Structure and Function
This is the group of animals that first developed nerves and muscles that create movement. It is also the first group organized on the tissue level, with both nerve and muscle tissue. They do not have organs.
Cross Cutting Concepts: Structure and Function
The body plan animation visualizes the complex cnidarian structures and how they function:
Many cnidarian species have two different body forms during their lives. One is the free-swimming form, called the medusa (a jellyfish for instance). The other is an attached form called the polyp (which resembles a tiny sea anemone).
Both forms have a single opening that serves as the mouth and anus. A ring of feeding tentacles typically surrounds the opening. The tentacles are packed with stinging cells, which contain nematocysts that shoot out a barbed shaft to catch prey. The nematocyst can even inject toxins.
Cnidarians have a top and a bottom. Their bodies are made up of two layers of tissue that include nerve and muscle cells. This body, with both muscles and nerves, allowed ancestral cnidarians to be the first animals on the planet to move.
The longest animal in the world is a cnidarian! Praya, a pelagic jelly, can reach a length of 120 feet.
Nematocyst: the specialized capsule that contains a coiled, hollow, usually barbed thread. The thread explodes out from the capsule when stimulated by predator or prey. Nematocysts can inject toxins into their prey.
Pelagic: living in the waters of the open ocean