How else to do battle with hair algae

[Delphinus]

That's my best guess but it doesn't look quite right. The distribution for the species is Carribean and eastern U.S. seaboard so that fits. But the "needles" don't look quite right and also the max size seems a bit larger than what this is (test max 85mm, overall size 110mm) which is about twice as large as what this one is. Maybe he's still a young'un..

See how the needles are quite stout looking, mine doesn't have those:


Anyhow, sorry for the hijack/tangent there Catherine .. Whatever this urchin is that I've got, he's been a good algae muncher.