Starfish

09 August 2019 | Posted in Charlotte Owen , Marine
Starfish
Common Starfish © Ryan Greaves

By Charlotte Owen

WildCall Officer

Starfish are among the most ancient life forms on the planet.  The earliest fossils date back 450 million years to the Ordovician Period, long before the dinosaurs, when invertebrates ruled the world – or rather, the oceans.  All life was aquatic back then and it was flourishing, with new species appearing at such a rate that global biodiversity skyrocketed.  The warm, shallow seas were teeming with weird and wonderful creatures from trundling trilobites (giant armoured marine woodlice) to predatory nautiloids (shell-dwelling squid), brachiopods (prehistoric oysters), tymbochoos (tube-dwelling worms) and bizarre echinoderms – the ancestors of today’s sea urchins, sea cucumbers and, of course, starfish.

Named for their pleasing symmetrical shape, starfish are more accurately known as seastars and there are some 2,000 species alive today.  Most have five arms radiating from a central disc, some have as many as 40 but they are all as bizarre as their ancestors. 

Starfish don’t have a brain or a central nervous system but they do have eyes, unusually located on the tip of each arm.  For a long time, scientists puzzled over whether and what a starfish could see, given the simple structure of their primitive eyes and lack of central processing power, but most can detect changing light levels and some can form rough images of their surroundings to aid navigation and find their way home.

Starfish don’t have any blood either, instead pumping seawater through their bodies to deliver key nutrients to their vital organs.  Water is also pumped into the hundreds of tiny tube ‘feet’ on each arm so that starfish can move along the sea bed, often surprisingly quickly.  The mouth is located on the underside of the central disc but it’s so small that a starfish feeds on large prey by ejecting its stomach, beginning digestion outside its own body before reabsorbing a stomach full of liquid lunch.  Starfish also have amazing powers of regeneration.  They can shed and re-grow their limbs to avoid becoming lunch themselves and, incredibly, a severed arm is capable of growing into an entirely new, genetically identical starfish - so even if the parent is eaten, its clone will live on.

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