Blue Moon: Moon Jellyfish

Blue Moon: Moon Jellyfish

You can see right through moon jellyfish — but that doesn’t mean they don’t have secrets.

This article was written for theJuly 2018 issue of Texas Parks & Wildlife Magazine. Read it here

From their phoenix-like regeneration ability to their inscrutable species identity, ethereal Gulf of Mexico moon jellies hide mystery within their translucent bodies.

Moon jellies are circular, with bells domed like umbrellas. Adorning their tops are luminous four-leafed clovers (the jelly’s reproductive organs). Moon jellies don’t have long trailing tentacles but instead sport short, fringe-like cilia around the bell, and four thicker oral arms hanging below. The jellies use their cilia to sweep in food toward a mucus layer on the edge of the bell.

Although they do have stinging cells in their tentacles, moon jellies rarely sting.

moon jellyfish

The life cycle of a moon jelly is convoluted — less like a cycle and more like a web. At different parts of their life cycle, moon jellies are jelly bean-sized larvae, plant-like polyps and translucent, bell-shaped jellies; they can sometimes skip a step or revert back to a previous one.

The moon jellies you might see drifting in the Gulf are the adult form, called the medusa, presumably because of their snaky tentacles. Female adults lay eggs that grow into tiny larvae called planulae. They will sprout into a plant-like polyp stage and reproduce asexually this time, growing new baby medusae — called ephyrae — one on top of the other, like a stack of pancakes. Every so often one will pop off and become a baby medusa.

To add to the confusion, moon jelly polyps can go dormant for up to 25 years. Even when a jellyfish dies, that might not be the end — researchers have observed polyps growing from dead medusas.

Austin-based science writer Juli Berwald, who recently published a book on jellyfish, Spineless, says there’s no telling what species you may see in the Gulf without genetic testing. Where scientists once assumed there was one species of moon jelly, there are actually eight, and maybe more.

“It’s cool that all these species masquerade as what one thing looks like,” she says.

So when you see a delicate moon jelly off the Texas coast, remember that scientists are even now uncovering new insights about these creatures, and there is still much to learn.

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