Urchin hitchhiker ID

[lv-reefer]

I got this guy the size of a pencil eraser when I got my FL live rock. Now he's like 4 inches around. What kind of urchin is he?

 

[bigarn]

Looks like a rock boreing urchin.....Not sure though.

 

[wrassecal]

Spiny Sea Urchin, Centrostephanus rodgersii - long, needle-like spines, which it wedges in cracks and crevices to secure itself to rocks. The spines may have a green iridescence, while the body varies in colour from deep red to black