Which of these animals possesses a gastrovascular cavity?

The presence of a gastrovascular cavity is a key characteristic of certain simple organisms, particularly those in the phylum Cnidaria, such as hydras. The gastrovascular cavity serves multiple functions: it acts as both a digestive chamber and a circulatory system, allowing for the distribution of nutrients throughout the organism. This cavity is typically open at one end and has a single opening that serves as both mouth and anus.

In the case of hydras, they rely on their gastrovascular cavity to facilitate both digestion and the transport of nutrients directly to the body tissues, which is efficient for their small, simple body structure. This adaptation is particularly suitable for aquatic environments where they are found.

Other animal groups mentioned, such as birds, mammals, and insects, have more complex body structures that include specialized digestive systems with distinct organs—like stomachs and intestines—that perform these functions separately. Thus, hydras are uniquely equipped with a gastrovascular cavity reflecting their evolutionary adaptations.