Which of the following phyla includes jellyfish, corals, and hydra?

The phylum that includes jellyfish, corals, and hydra is indeed Cnidaria. This group of animals is characterized by their unique body structure, which includes specialized cells known as cnidocytes. These cells contain nematocysts, which are stinging organelles that allow these organisms to capture prey and defend themselves.

Cnidarians primarily exhibit two body forms: the medusa, which is typically bell-shaped (as seen in jellyfish), and the polyp, which is usually tubular (as seen in corals and hydra). This phylum also encompasses a diverse range of organisms that share fundamental biological features, such as radial symmetry and a simple body plan, which plays a crucial role in their ecological functions.

The other phyla listed do not include these organisms. Platyhelminthes refers to flatworms, which have a different morphology and biological functions. Arthropoda includes invertebrates with jointed limbs and an exoskeleton, such as insects and crustaceans. Chordata is the phylum of animals with a notochord, which includes vertebrates like mammals, birds, and reptiles, but does not encompass cnidarians. Thus, Cnidaria is the correct classification for jellyfish