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Nature Notebook – Planarian

The inky black organism moving across the pond observation tray looked like a period then an arrow then a period. That movement and the arrow-shaped head helped the students realize they had caught a planarian.

The auricles that give the planarian its distinct arrow shape have chemoreceptors to help it find food (alive or dead). Its tiny eyes are only capable of sensing light. It glides over surfaces on tiny hairs called cilia.

It can be hard for a tiny flatworm to find another when it is time to reproduce. Planaria have an interesting method of dealing with that problem. They pull themselves apart…literally. It attaches the tail to a surface then pulls its head away until it separates. Each part then regenerates a new head or trail. A new planaria can develop from pieces as small as 1/270th of the original organism!