Sea urchins have a ball-shaped appearance with long and sharp spines. Some might be more familiar with their other nickname, sea hedgehogs. They can be found on substrates like coral or rocky reefs, alone or in impenetrable masses.
These omnivorous echinoderms feed on algae, detritus and other invertebrates. They eat with their set of powerful teeth, called the Aristotle's lantern. Some species have even shown nocturnal feeding behaviour, while they hide when the sun is up. Apart from its role as algae grazers, certain species may be home to smaller creatures such as shrimps, cardinalfishes, razorfish and snails.