Sea urchin

Sea urchins are mostly omnivorous with a tendency towards being herbivores; they eat algae but will not refuse a piece of mussel or fish flesh. This characteristic makes sea urchins versatile and efficient detritivores. Sea urchins possess an Aristotle's lantern, which is a specific arrangement of their teeth. Their teeth grow throughout their lives (like rodents), which means that sea urchins scrape the surface of rocks to erode their teeth. This has the side effect of reactivating the bacteria present in the rocks and removing the coralline on the surface, allowing water to pass through for proper filtration. This is beneficial for the aquarium.