noun. free-swimming mostly freshwater flatworms; popular in laboratory studies for the ability to regenerate lost parts.
1. Noun, singular or mass When a planaria is cut into pieces, each piece is able to regenerate into a fully formed and functional individual organism. 2. Noun, plural While they don't have true "eyes", many species of planaria have what are called "eye spots" where there are clusters of photoreceptors that can sense light. 3. Verb, non-3rd person singular present By definition, planaria actually refers to many species of flatworm under the class of flatworms called "Turbellaria".