Magical Comb Jellies

When I was a kid, my babysitter was a witch. She was a typical pointy-hatted, spell-casting witch. But she was also a marine biology major at Humboldt State University, so she’d take me on her broom to the beach after school to look for washed-up stuff. 

One day she said, “Look, my lovely, the beach is covered in Satan’s testicles!”

Thousands of marble-sized clear blobs were washing in. She said, “Sorry, they are actually called ‘comb jellies.’ See, I used to date a guy named Satan, so I knew I couldn’t trust him. I cast a spell so that if he ever cheated on me, his testicles would turn into exploding glass marbles engineered to shred his scrotum. Um, this species of comb jelly looks like our common Pacific sea gooseberry (Pleurobrachia bachei).”

I didn’t understand any of this, but I liked marbles and explosions, so it sounded fun. 

Then she said, “Comb jellies are jellyfish-like, but most scientists believe they are unrelated to typical umbrella-shaped jellyfish. And the comb jellies are currently placed in their own phylum — Ctenophora — which means they aren’t part of any other animal group. However, some scientists argue that jellyfish and comb jellies may have branched off from a common ancestor. Either way, they are ancient — both groups have been around for at least 500 million years.”

She continued, “But there are only about 200 species of comb jellies in the world. Compare that to the phylum Arthropoda, which includes insects, spiders and crustaceans, and includes millions of species as diverse as black widows and praying mantises. The diversity of comb jelly body types is low, but while most are bulbous, there’s a ribbon-like species in the tropics that can reach 5 feet long. And there’s another with a big mouth that feeds primarily on other comb jellies.”

Then we scooped some up and flew to the marine lab to put them in a tank. “See how they have those eight rows of colorful little hairs on the sides of their bodies? Those hairs are called ‘cilia’ and they beat in sequence up and down the animal’s body so it can swim. The cilia split sunlight like a prism, which produces that beautiful pulsing rainbow effect.”

She pointed out the two feathery tentacles hanging from either side of the animal. “Those are the feeding arms,” she said. “Unlike jellyfish, the arms don’t have stinging cells. Instead, they have sticky cells that capture small planktonic animals, which the arms then carry to the comb jelly’s mouth. And the comb jellies can reproduce quickly when prey is abundant, so population explosions are common in the summer. In fact, they can become so dense that they eat up all their prey and the prey of other species in an area. They can even gum up fishing gear and marine infrastructure.”

I pointed out they were slow swimmers and weren’t exploding. She pointed out that I was getting cranky and needed a snack. But first she said, “Yes, comb jellies mostly drift with currents. The beating cilia mainly help them orient to improve feeding efficiency. However, when prey becomes scarce, they can fold their tentacles inside through their mouth to swim more quickly to find food.”

While having my snack, I asked what happened to her boyfriend. She said, “His testicles exploded, so I dumped him.”

My babysitter witch earned her marine biology degree and became a career professional with one of the federal oceanic agencies. But some wacky billionaires seized control of the government and fired her without giving a reason. 

I pity the billionaires whose testicles she is now contemplating.

Biologist Mike Kelly (he/him) is also the author of the book Tigerfish: Traditional and Sport Fishing on the Niger River, Mali, West Africa. It’s available at Amazon or everywhere e-books are sold.

This article appears in Burger Week 2025.