Pencil Urchin

The pencil urchin (Eucidaris tribuloides) is a Caribbean/western-Atlantic species with thick, blunt "pencil" spines it uses to wedge into rock crevices — genuinely different from the other two in one important way: it is an opportunistic omnivore documented eating coral tissue, clams, sponges and other sessile invertebrates at night, especially once algae runs low, so it belongs with reef_safe: caution rather than the typical CUC "yes." It still grazes nuisance and coralline algae effectively and can dislodge unglued rock while moving. Peaceful and not venomous toward keepers despite the heavy spines, but — like all echinoderms — cannot tolerate copper-based medication and needs an established, well-fed tank to stay off corals.