A study published Nov. 1 finally answered a millennia-old question: what the heck are starfish and other members of the echinoderm family?
Echinoderms are things like sea urchins, sea cucumbers, and the aforementioned starfish. We love these little oceanside friends (except urchins), but it turns out scientists only just discovered what they actually are, and how they evolved such strange bodies.
While most animals develop bilaterally, having two symmetrical sides, echinoderms somehow evolved a radial body, according to a study published in the journal Nature. Their bodies grow around a central axis, with body parts sprouting off at each point, like what we see with a five-pointed starfish.
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“Although a slight oversimplification, the findings suggest that one could think of the body of a starfish (at least in terms of the anterior–posterior identity of its surface tissues) as a disembodied head walking about the sea floor on its lips — the lips having sprouted a fringe of tube feet, co-opted from their original function of sorting food particles, to do the walking,” University of Saskatchewan biologist Thurston Lacalli said in a press release regarding the discover, though he was not involved in the original study.
Despite the shape of sea cucumbers, they too appear to have a radial body plan. It’s like a “stretched out head laying on its side,” researchers noted to LiveScience. (RELATED: Forget Sharks, This Is The Scariest Thing Happening In The Ocean)
So the next time you see a starfish, urchin, or sea cucumber, please remember that it is mostly made up of heads … as if the ocean wasn’t weird and scary enough.