planária

Planaria are a group of free-living flatworms belonging to the class Turbellaria, though this classification is now considered paraphyletic. They are found in both freshwater and saltwater environments, as well as terrestrial habitats, typically in damp conditions. Planarians are characterized by their dorsoventrally flattened bodies and a distinct head with two eyespots that detect light. They possess a pharynx, which is everted from a ventral opening, used to ingest food.

A remarkable feature of planarians is their extraordinary regenerative ability. If a planarian is cut into pieces, each piece can regenerate into a complete, new individual. This regeneration is due to the presence of undifferentiated stem cells, called neoblasts, distributed throughout their bodies. This characteristic has made them a popular model organism in scientific research, particularly in the fields of developmental biology and regeneration.

Planarians are carnivorous or scavengers, feeding on small invertebrates, dead organic matter, and algae. They move using cilia on their ventral surface, secreting mucus to aid in locomotion. Reproduction can be asexual through fragmentation or sexual, with most planarians being hermaphroditic. Their simple body plan and potent regenerative capabilities continue to fascinate scientists and contribute significantly to our understanding of biological processes.