Starfish — more accurately sea stars, since they aren't fish — are among the ocean's strangest animals, moving without a brain and eating without teeth.
Here are the verified facts.
Starfish aren't fish; scientists prefer 'sea stars' since they're echinoderms, related to sea urchins and sand dollars.
Sea stars have no brain and no blood; they run on a water vascular system that pumps seawater to move their tube feet.
Most sea stars can regenerate lost arms, and a few species can regrow an entire body from a single arm and part of the central disc.
There are around 2,000 species of sea stars, living in every ocean from the tropics to the poles.
While the classic sea star has five arms, some species have 10, 20, or even up to 40.
Sea stars eat by pushing their stomach out through their mouth to digest prey like clams and mussels externally, then pulling it back in.
They have eyespots at the tip of each arm that detect light and dark, helping them navigate.
Sea stars move on hundreds or thousands of tiny tube feet powered by water pressure.
The crown-of-thorns sea star is a coral predator that can damage reefs during population outbreaks.
Sea stars can right themselves if flipped over, slowly twisting their arms until they flip back.
Some sea stars can live up to 35 years.
A sea star's skin contains hard calcified plates and often spines for protection.
Sea stars breathe through their skin and tube feet, absorbing oxygen directly from seawater.
A wasting disease has killed enormous numbers of sea stars along the Pacific coast since 2013, reshaping some coastal ecosystems.
Sea stars are keystone predators; the very concept of a 'keystone species' came from studies of the ochre sea star.
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