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Even in the strange world of marine invertebrates, the starfish is undoubtedly one of the ocean's most surprising creatures. The hundreds of little tubular feet on their underbellies are just one of many anatomical marvels. Starfish are particularly unique in that they lack brains and blood – instead, they have a decentralized nervous system spread out through their arms and rely on filtered seawater for transporting nutrients.
There are nearly 2,000 species of starfish spread across the world's oceans, and they come in a variety of shapes, colors, and sizes. You'll find them in tropical seas as well as polar regions, and at a huge range of depths. Starfish are not actually fish, so scientists prefer to refer to them as "sea stars." Like sea urchins, sea cucumbers, and sand dollars, starfish are echinoderms.
Rather than a centralized brain, a starfish has a nerve ring surrounding its mouth which connects to nerves throughout its arms. This nervous system design puts the sea star’s arms in charge. Every sea star has a dominant arm that communicates which way the organism should move. Its tubular feet follow the orders, establishing a rhythm of movement. Researchers believe that the complexity of a sea star’s nervous system could one day lead to advancements in robotics.
The strange stars of the sea:
- Sea stars have eyes on the tips of their arms, allowing them to differentiate between daylight and darkness.
- Starfish can live for up to 35 years and can weigh up to 11 lbs (5 kg).
- A starfish is capable of regrowing a limb if it happens to lose one, though the regeneration process can take up to a year to complete.
- When a sea star eats, its stomach is evacuated through its mouth to digest the food, then returns to the inside of the body when the meal is finished.