chickenfeet

So? "urchin"="hedgehog" anyway, from "oursin", and only got applied to scruffy kids recently. It's dying out in English dialects but is still around in some, and it's the ones that use it that gave rise to "sea urchin", the rest using the pure English "sea hedgehog" (I don't think I've ever actually come across "sea hedgepig" but that would be another possibility).

I'm just surprised that you're surprised!