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Scientists discover jellyfish species that produces stinging mucus grenades

by Jackie King

People Editor

A study published in Communications Biology magazine on Feb. 13 revealed astounding new information about a species of jellyfish that live in mangrove forests from Florida to Micronesia. These Cassiopea jellyfish do not need to touch their victims in order to sting them, instead relying on clouds of mucus deemed “mucus grenades.”


Cassiopea xamachana, commonly known as the “upside-down jellyfish,” spews mucus as it rests on the ocean floor. (Wikimedia Commons)

These jellyfish, termed “upside-down jellyfish,” have been under the microscope for almost a century, but this is the first report that has fully explained the effect of the magical goo. Marine biologists now understand how these creatures are able to harm swimmers from a distance. 

Co-lead reporter Cheryl Ames, a marine biologist from the Smithsonian National Museum of Natural History, explained that scientists “knew it had to be something in the mucus.” Her team discovered that the jellyfish produce a TON of sticky mucus to trap their prey, a strategy comparable to spider’s webs. This mucus is harmful to nearly all sea animals that lack protective shells, including humans. Ames’s team compares the jellyfish to “little Roomba vacuums…bumping into the brine shrimp…just killing them on contact, and moving on to the next.”


Several upside-down jellyfish cluster together under the roots of a mangrove tree for protection from predators. (Wikimedia Commons)

Despite not necessarily coming in contact with these jellies, when humans dive anywhere near them, they often experience what is known as the “stinging water sensation” anywhere skin is exposed. Although the sensation is usually just an annoying itch or burn, Ames and her team revealed through laboratory tests that extended exposure to the venom can be detrimental to health.

The team of scientists deemed the mucus grenades “cassiosomes,” describing them as “microscopic pieces of popcorn.” Each structure is made of a jelly-filled center, a number of nematocysts – or stinging cells – and anywhere from 60 to 100 hair-like cilia that allow the cassiosomes to swim through the rough and dirty ocean to find their mark. At first glance, researchers believed that the goo structures were parasites, but after careful examination, they realized that the same stinging cells in the cassiosomes were identical to the stinging cells found on the upside-down jellyfish’s body. 


A group of Cassiopea xamachana float together in a tank at the Monterey Bay Aquarium in Monterey, California. (Wikimedia Commons)

The team found these cassiosomes in four other jellyfish species, leading to the theory that they might be common in jellies. Anna Klompen, a jellyfish biologist completing a Ph.D. at the University of Kansas and a co-lead author on the study, revealed that they also discovered algae in the cassiosomes, although they “really don’t know what the algae are doing [inside the cassiosomes],” but it is clear that they help provide the jellyfish with energy much like a battery pack.

(Sources: USA Today, Mercury News)

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