Planarian

A planarian is a small, flat worm about the size of a grain of rice that has fascinated scientists for centuries due to its remarkable regenerative abilities. These creatures can be cut into pieces and regrow into complete, fully functional worms, making them invaluable for studying how organisms repair and regenerate damaged tissue. Planarians are also noted for having primitive brains and the ability to learn, which helps researchers understand the fundamental principles of how nervous systems work and evolve.