Pencil Urchins, Image coming soon. Sea Urchins are incredible powerhouses when it comes to clearing algae out of a reef. These echinoderms, related to starfish, venture around on their countless tube feet as they use their small, conical ring of �teeth� to scrape algae, sponges, and other particulate foods off of most tank surfaces. Urchins are typically quite active and ravenous, and a single individual can make a huge impact on the presence of both encrusting and filamentous algae in both reef and fish-only systems. While reef-safe, it is highly recommended that any loose corals be glued down, as sea urchins in general have a tendency to accumulate objects to use as a sort of �cover� from predators. If considering introducing an urchin to a fish-only system, be aware that some larger wrasse, trigger and puffer species are capable of consuming urchins.