Final answer:
A gastrovascular cavity is a digestive system with a single opening that serves as both a mouth and an anus. Organisms with this cavity do not need a cardiovascular system because it serves both digestive and circulatory functions.
Step-by-step explanation:
A gastrovascular cavity is a digestive system consisting of a single opening that serves as both a mouth and an anus. This arrangement is called an incomplete digestive system. In organisms with a gastrovascular cavity, extracellular digestion occurs as food is taken into the cavity, enzymes are secreted, and the cells lining the cavity absorb nutrients.
These organisms do not need a dedicated cardiovascular system because the gastrovascular cavity serves both digestive and circulatory functions by distributing nutrients throughout the body.