The Animal That Survives Without a Brain: 9,000 Species, Zero Neurons

Sea sponge growing on a reef — A sea sponge: no brain, no heart, no organs — and it filters thousands of litres a day. Photo: Twilight Zone Expedition Team 2007, NOAA-OE — Public domain

Push a living sea sponge through fine mesh and its cells crawl back together to rebuild a working animal. No brain, no nerves, no organs, and a lineage older than fish and dinosaurs.

Colourful coral reef scene — Sponges are among the oldest animal lineages still on the reef. Photo: Richard Ling <[email protected]> — CC BY-SA 3.0

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Photography credits: Twilight Zone Expedition Team 2007, NOAA-OE (Public domain) via Wikimedia Commons