Range: Tropical and temperate oceans worldwide Habitat: Coastal waters Size: Up to 12 inches (30cm) long across the bell Diet: Fish, worms, crustaceans, and more Threats: Large fish, crabs, sea turtles, and more Life span: About one year as adults

Transcript:

Today on Animal Fact Files we’re discussing box jellyfish. Box jellyfish are called so because they are boxy in shape; even their scientific name is in reference to their square structure. While these animals are certainly stinging cnidarians, they aren’t technically “true” jellyfish as they aren’t classified in the same order as true jellyfish, though they have some similarities to true jellyfish such as their life cycle.

What most people consider a “jellyfish” is the adult, or medusa, stage of the jellyfish’s life cycle, but these animals start out as eggs. Box jellyfish mate with a male inserting his tentacles into a female’s mantle where he’ll release sperm and fertilize her eggs. There are just over 50 classified box jellyfish species as of this recording though more research will likely reveal more. Some species release their fertilized eggs into the water column where they’ll hatch within a few days, females of other species brood their eggs inside their bodies and they’ll release the larvae after they hatch. The larvae settle to the seafloor and develop into polyps which can reproduce asexually and eventually transform into the adult form, the free swimming medusa.

Something that sets box jellyfish apart from true jellyfish is that they are actually efficient swimmers. These cnidarians can move as fast as 20 feet (6m) per minute and will actively avoid objects in the water if confronted with them. They’ve even been observed avoiding capture from humans. And the reason they can perceive objects in the water? Box jellyfish have eyes - quite a few, actually.

Box jellyfish have three types of eyes, two are not complex and are more like eye spots that mostly detect light. Their other eyes, however, are complex, and kind of resemble the eyes found in vertebrates. It’s believed they can even perceive color. It’s likely these complex eyes help them navigate their habitats which tend to be found closer to shore where obstacles like branches, roots, and debris could snag planktonic jellies. What’s fascinating about the box jelly’s complex eyes, though, is that these animals have no brain, so scientists aren’t really sure how the box jellyfish interprets the signals the eyes pick up.

Having eyesight may help them escape predators as box jellyfish have been observed swimming away from objects in the water. That doesn’t mean they have no predators. Large fish, crabs, sea turtles, and more all eat these cnidarians. In size box jellyfish may have a bell up to 12 inches (30cm) in length and tentacles reaching up to ten times that. Box jellyfish tentacles can pack quite a punch. They paralyze their prey in their tentacles, and these prey can include: fish, worms, crustaceans, and more. Some species are so potent they’ve caused human fatalities as they induce cardiac arrest within minutes, though not all box jellyfish species are this dangerous to people.

Their tentacles are helpful in determining the species as some have just four dangling tentacles from each “corner” of their box shaped body while others have groups of tentacles hanging from these corners. Box jellyfish are found in tropical and temperate oceans throughout the world as far north as California and Japan and as far south as New Zealand and South Africa. Like true jellyfish, box jellyfish generally don’t live longer than a year as adults.

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