Starfish (also known as sea stars in the scientific world) are curious creatures spread out across rock pools, seagrass and coral reefs. Some are even found 9,000m deep on the sandy seabed. They come in various shapes, sizes and colours - there are over 1,600 species - most commonly with five arms, but this is not always the case. If you're curious about how these colourful characters move without a brain or turn themselves inside out to eat, read on for our top starfish facts...
Star not fish
Let's kick off with a slightly confusing fact about starfish. They're not fish. Despite their common name, starfish are an echinoderm closely related to sand dollars and sea urchins. Due to this classification, the scientific world has undertaken the (tricky) task of trying to rename them 'sea stars'.
No brain or blood, no problem
Starfish lack brains, but this doesn't hold them back. A central nerve ring coordinates their movements, sending signals to their arms in response to light, touch and chemical sensors. This is how we see them travelling on their tube feet around rock pools. In the absence of blood, starfish use seawater, which delivers key nutrients to organs, allowing them to function correctly.
Life span
Across the many, many species of starfish (over 1,600 remember), there are a range of life spans. Typically, a starfish will live between five to ten years, but some species can live up to 35 years in the wild.
Regenerative skills
One contributor (and a well-known starfish fact) to this long-life span is that these multi-limbed marvels can regrow lost limbs. If they lose an arm, they can grow it back, though it might take a few months to a year. Even if a part of the central disk (the main body) is lost, some species can regenerate a whole new starfish from just an arm and bit of disk. This happens because of special cells that multiply and form the needed tissues. Thankfully, starfish have a good immune response to keep infection at bay while they heal.
Many hands...
Starfish are recognised by their five arms. But did you know that the number can vary widely depending on the species? Some starfish have as few as four arms or as many as 40. For example, the common starfish (Asterias rubens) typically has five arms, while the sun star (Solasteridae family) can have up to 15 or more. Their arms are covered in tiny pincer-like organs and suckers, which help them slowly move along the ocean floor. They also have eyespots at the tips of their arms that let them sense light and dark, helping them find food.
Inside out
Starfish have more than just extra arms. They also have two stomachs: the cardiac stomach and the pyloric stomach. The cardiac stomach is where a starfish appears to turn itself inside out in their quest for food. It can come out of the starfish's mouth to grab and start digesting food, like clams, right on the spot. After that, it pulls the partially digested food back in and passes it to the pyloric stomach, where digestion finishes and nutrients can be absorbed.
Predator evasion
Starfish have developed several savvy ways to evade predators in the vast ocean. They can camouflage themselves against the ocean floor, making them practically invisible to predators. On top of that, some starfish have toxic chemicals in their bodies that make them taste bad or even harm predators, giving attackers a good reason to think twice before chomping down. And let's not forget their tough, spiny skin-like natural armour; it shields them from physical harm.
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