Question

How many body openings do cnidarians have?

Answer 1

Cnidarians have a simplified digestive system with a single body opening that functions as both mouth and anus, surrounded by tentacles with nematocysts for prey capture, and they come in two body plans: polyp and medusa.

Step-by-step explanation:

Cnidarians are a group of aquatic invertebrates known for their distinctive body structures and radial symmetry. These organisms have a simplified digestive system compared to more complex animals, which is characterized by the presence of a single body opening. The gastrovascular cavity of a cnidarian, such as a hydra or jellyfish medusa, serves both as the entrance for food intake and the exit for waste. This single opening is surrounded by tentacles, which bear specialized cells called nematocysts used for capturing prey. The internal cavity, known as the coelenteron, serves as a site for digestion, nutrient absorption, and gas exchange. Cnidarians showcase two body plans: the polyp, which is sessile and generally has the mouth opening facing upwards, and the medusa, which is free-swimming with the mouth and tentacles dangling from the bell-shaped body.

Answer 2

Cnidarians have one body opening. There is no mouth or anus. Instead, food particles are drawn into the body by movement of water. Inside the body cavity are specialized cells called amoebocytes and collar cells that help digestand remove wastes. Cnidarians with the opening at the top have body plans called polyps, such as corals. Those with the opening underneath have a medusa body form, such as jellyfish.