Cannonball Jellyfish

Pictured here is a cannonball jellyfish. Notice the brown coloring around the bottom of its bell.

Domain: Eukarya
Kingdom: Animalia
Phylum: Cnidaria
Class: Scyphozoa
Order: Rhizostomeae
Family: Stomolophidae
Genus: Stomolophus
Species: Stomolophus meleargis

For today’s species we’re going to head back to the phylum Cnidaria! Honestly, it’s one of my favorite phyla because it has coral, jellyfish, and siphonophores which are all really cool creatures to check out. So let’s go ahead and cannonball into today’s topic…

I’m trying too hard again, aren’t I?

Stomolophus meleagris, also known as the Cannonball Jellyfish, is aptly named because it is about the size and shape of a cannonball used to load cannons in the days of massive sea voyages, pirates, and colonization.

Though, compared to cannonballs, S. meleagris can be a lot prettier to look at. They range in color from white to brown and will have very neat looking markings of various colors around the bases of their dome heads. Unlike other jellyfish, cannonball jellies don’t have tentacles. Instead, they have short, forked oral arms that extend out and away from the dome a little.

Cannonball jellyfish are native in both the Atlantic and the Pacific oceans, found right off the coast and in estuaries. They’re most abundant in the waters off the southeastern United States and the Gulf of Mexico. S. meleagris populations span from New England to Brazil in the Atlantic Ocean, and from the Sea of Japan to the South China Sea in the Pacific.

In fact, they are considered a common menu item in Asian markets and are dried and processed right after capture. Humans aren’t the only species that eats these guys; the most important is the endangered leatherback turtle, which only eats S. meleagris.

The jellies themselves eat macrocrustaceans, certain fish larvae, and zooplankton; and they eat by sucking water in where several tiny “mouths” are located. Fun fact: their scientific name roughly translates to “many mouthed hunter”.

Like other cnidarians, these guys do have stinging cells, however they don’t pose much of a threat to people. The pain of their stings isn’t too great, and it will cause mild irritation though, if you get stung in the eye that is a whole other can of worms—so make sure you always wear protective eyewear when in the ocean!

I first saw these jellies in aquariums growing up, and I always thought they looked a little goofy. I love watching them move about their tanks, and I can watch them for hours—just ask my husband!

I’ve never seen these guys while diving or snorkeling, which is a little disappointing, but there’s always next time. I’ve also not come across them while playing in the ocean on beach days, though I have seen plenty of them wash up on the sand. In fact, during one of my internships, I watched a few of them get pulled into estuaries during high tide, and it looked like they were just rolling with the current like a runaway cannonball!

Sources and cool links: (totally check this out, it has a lot of good information!) (this one also has more links and things to check out at the end.)


Golden Jellyfish

Photo of a Golden Jellyfish taken by Dr. Alexander Mustard. More of his photos can be found at

Domain: Eurkaryota
Kingdom: Animalia
Phylum: Cnidaria
Class: Scyphozoa
Order: Rhizostomeae
Family: Mastigiidae
Genius: Mastigias
Species: papua etpisoni

Last time, we talked about Jellyfish Lake in the Palau region of the Caroline Islands archipelago. We learned that the meromictic lake, which has distinct layers of water that do not intermix, is the only place you can find Golden Jellyfish.

I highly recommend putting this place on your bucket list, not only would you get killer pictures but you’ll experience something unlike anywhere else in the world! Now, let’s move on to the special guest of the day.

Golden Jellyfish (Mastigias papua etpisoni) are a species of jellyfish that are closely related to the spotted jellyfish that can be found in the lagoons near Jellyfish Lake. Like coral, they benefit from a close relationship with zooxanthellae. What, did you think coral were the only ones to be best friends with the greatest algae of the ocean?

Like coral, the jellyfish house the zooxanthellae in their tissue which gives the jellyfish their golden color. They also have a mutualistic relationship with the algae; the golden jellies provide housing, waste that the algae uses for nutrients, and sunlight in exchange for the sugar that the zooxanthellae don’t use from photosynthesis.

In fact, it’s the sugar that gives the jellies all the energy they need to grow and reproduce, because they don’t gather food on their own since they lost their ability to sting prey through untold years of evolution. It also allows them to propel and migrate through the water, giving the zooxanthellae access to sunlight throughout the day as the sun moves across the sky, casting shadows on the lake.

This migration has a positive effect on the lake’s ecosystem, by stirring up the nutrients and microorganisms found in the water, providing one of the only sources of circulation in the layers they inhabit. So in this scenario everyone wins: the zooxanthellae get everything they need to make food, the jellies get all the leftovers, and the surface of the lake gets stirred up for the other organisms that call it home.

But the jellies aren’t without predators. They’re preyed upon by anemones that concentrate in areas that the jellies frequently migrate through, creating a bottleneck effect. Thankfully, the sheer number of Golden Jellyfish provide their predators a healthy diet without affecting the population too much.

I find these guys to be really cool creatures to study just because of their relationship with the zooxanthellae and their ecosystem. In general, the whole lake is fascinating and worth the time to read about. It’s a wonderful example of how crazy nature can become when isolated from what used to be similar environments and/or species.

Sources and cool links to check out: