Slate pencil urchins (Eucidaris tribuloides) -- sometimes known as club urchins or mine urchins -- belong to the taxonomic class Echinoidea. Although these spiny creatures look as though they have no eyes, legs or method of moving themselves, they're surprisingly mobile when they choose to be.
What They Look Like
At first glance, slate pencil urchins just look like a big ball of spines, but there's more to them than that. They usually reach a diameter of 5 to 6 inches. Their thick spines -- which offer them some protection from predators -- are attached to a globular center. They range in color from brown to red or tan, with dull white spines. It's on their undersides where it gets more interesting -- they have hundreds of transparent tube feet to move them around and a mouth with five horny, toothlike wedges.
Where They Live
As marine creatures, slate pencil urchins can only be found in the ocean. More specifically, they live in the Caribbean and the Atlantic Ocean, from Bermuda to Brazil. Their most common habitat is in turtle grass beds, but they're also often found in reefs and coral crevices. They can be found at a range of depths -- although they're quite common in shallower waters, at around 20 feet deep, they've been collected at depths of up to 2,300 feet.
What They Eat
Although primarily herbivorous, slate pencil urchins are opportunistic feeders and will scavenge for other types of food. They generally come out at night to feed, moving around and using their hard, horned teeth to scrape algae and other plant matter off rocks and corals. However, they'll also eat sponges, barnacles, mussels and dead fish or other sea creatures.
How They Reproduce
Despite males and females looking exactly alike, slate pencil urchins have distinct and separate sexes. They reproduce using external fertilization. Females release eggs and males release sperm into the water simultaneously, where they will join and become fertilized. Females can produce thousands, or even millions, of eggs in one go. Once hatched, these tiny urchins start out their lives as larvae and take roughly two years to reach their full adult size.
Slate pencil sea urchins belong to the taxonomic phylum Echinodermata, which includes sea stars, sand dollars and sea cucumbers. As with other members of their phylum, they have five-fold radial symmetry, although it isn't obvious until you look at their dried shells. These urchins are fairly numerous and aren't considered threatened or endangered at this time.