The hitch hiker urchin has finally emerged from the rocks

[lessans]

I don't know if this is a pest urchin and how big of a threat it is toward my corals, but it has pointy spikes about 3/4" long. the spikes are a light brown color and the actual body surface is black with white around the base of each spike. The urchin body is about 1/2" in diameter. Can anyone I.D. this urchin from my description?

 

[greenbean36191]

Google Echinometra. They're probably the most common hitchhiking urchins, and they fit your description (well, so do lots of other urchins ). They're known as the rock boring urchins. They're harmless.

 

[lessans]

Yay, it's harmless! Just to let you readers know that I didn't just take greenbean36191's word for it, but I also researched Echinometra and discovered that my particular species is Echimetra mathaei. It is known to feed on red coralline algae and other tropical algae.