Starfish ‘arms’ are actually extensions of their head, scientists say

Starfish begin life as larvae with two-fold symmetry, before metamorphosing into their adult forms with a five-fold body plan. Photograph: Frank Hecker/Alamy

Starfish may appear to have a plethora of limbs, but it turns out the creatures actually resemble something akin to a disembodied head.

Experts say it has long been a conundrum how starfish, sea urchins and other animals with a fivefold body plan, known as echinoderms, evolved from an ancestor with twofold symmetry – a body plan common today in animals including insects, molluscs and vertebrates.