Yes, I know exactly what this is - a sea urchin (the Maori's call them 'kina'). They are a delicacy (not to me!) & people can be seen gathering them to eat at low tide. And seagulls love them too. I like watching them in the rockpools with all their spines attached & waving. :o)

Does a sea urchin look like a starfish because that's what I would have guessed?

it is an urchin, but not a fossil...probably the aftermath of a seagull