Do starfish have arms or legs?

Starfish appendages are among the most versatile in the animal kingdom, so to call them either arms or legs is a disservice.

Bloody Henry starfish on golden star tunicate and sea sponge, Loch Roag, Isle of Lewis, Scotland, UK. © Paul Kay/Getty

Slow-crawling species defy mammal anatomy consistently. With 10, 40 or the classic five limbs, starfish – more accurately, ‘seastars’ – prowl the craggy intertidal zone, while brittle and basket stars prefer the deepest, muddy parts of the ocean.

Advertisement

The underside of each limb is studded with hydraulically operated tube ‘feet’, tipped with suction cups for feeding and locomotion. The suckers, up to 15,000 per animal, pry open bivalve prey, such as clams. Suction also enables seastars to ‘Velcro’ themselves to surf-pounded rocks.

Flipped upside-down, the animals right themselves with a slow-motion, ‘tripod’ breakdancing move. Eyespots at the limbs’ tips respond to light, while nearby suckers sense chemicals that betray a food source by its odour. Other receptors register touch, temperature, body orientation or seawater composition.

Yet another function is worth mentioning: sexual organs in each limb release eggs or sperm into the water.


Do you have a wildlife question you’d like answered? Email your question to wildquestions@immediate.co.uk or post it to Q&A, BBC Wildlife Magazine, Immediate Media Company, Eagle House, Bristol, BS1 4ST.

Advertisement

Main image: Bloody Henry starfish on golden star tunicate and sea sponge, Loch Roag, Isle of Lewis, Scotland, UK. © Paul Kay/Getty