Range: Tropical Indo-Pacific waters Habitat: Sandy or rocky bottoms, coral reefs, and seagrass beds Size: About 4 inches (10cm) in diameter Diet: Algae, bryozoans, and marine detritus Threats: Paracorynactis and more Life span: Unknown

Transcript:

Today on Animal Fact Files we’re talking about flower urchins. Flower urchins may look like a bundle of pretty flowers slowly meandering along the ocean floor, but these petals pack a toxic secret. Flower urchins are considered some of the most venomous sea urchins in the world, and it’s thanks to these fancy “flowers”.

There are four described species of flower urchins and they are found mostly in tropical Indo-Pacific waters. Flower urchins may be found along sandy or rocky bottoms, within coral reefs, or hanging out in seagrass beds. They populate coasts from eastern Africa all the way around to the West coast of North America, and are typically found in tidal zones down to about 300 foot (91 meters) deep waters.

Though one might venture to think the spines of these urchins, just like the spines in most other sea urchin species, would be their source of venom injection, this is not the case. Flower urchins are recognizable from other sea urchins because of their distinct blossoming appearance. Each “flower” on a flower urchin is actually a grabby little claw poised to inject venom into any would-be adversaries. In humans, this toxin has been known to cause temporary paralysis and pain - and most oceanic predators know well enough to leave these toxic bouquets alone. There are, however, some cnidarians who can handle the sting of a flower urchin and will eat them up if given the opportunity. This works out for the cnidarians because flower urchins can get pretty big!

On average, flower urchins can be four inches (10 centimeters) in diameter. They may also falsely appear larger than this because they perform covering behavior. When sea urchins cover themselves in oceanic debris, such as rocks or shell fragments, this is called covering. Sometimes it’s believed to help with protection, however, in the case of the already-well-protected-with-venomous-flower-claws flower urchins, this behavior is thought to either help keep them grounded to the sea floor in strong ocean currents or to assist in UV protection.

Flower urchins aren’t always covered, however; in the springtime, when flower urchins are preparing to breed, they’ll drop all their covering material and seek out a mate. Sea urchins in general are basically impossible to sex from their external characteristics and flower urchins are no exception to this. When they’re ready to mate, flower urchins release their sperm and eggs into the water column in an act of broadcast spawning. We talk about sea urchin spawning in a little more detail on our sea urchin episode if you want to check that out!

Though they are venomous, some animals literally live on flower urchins. Two types of crustaceans, one a small shrimp and the other a zebra-striped crab spend their lives living among the protective flower beds protruding from the flower urchin’s test. A “test” is basically the skeleton of a sea urchin; like sand dollars, flower urchins are echinoderms.

Flower urchins eat algae, sessile aquatic invertebrates called bryozoans, and marine detritus. Their mouths are located on the bottom of their bodies.

For more facts on flower urchins, check out the links in the description. Give a thumbs up if you learned something new today, and thank you for watching Animal Fact Files.