Jellyfish don’t just sting with their tentacles. In warm coastal waters around the world, if you are not properly dressed for the occasion, you may be better off staying away from areas where jellyfish of the genus Cassiopea are abundant. Why? Scientists have found that getting too close can cause irritating stings, even without direct contact because these jellyfish use clouds of mucus filled with microscopic poisonous “grenades.”
A team of researchers from the Smithsonian Museum of Natural History has discovered the microscopic structures in the mucus left behind by this very special jellyfish. And, although they do not know what role these small structures, called casiosomes, play in the ocean, they seem to be a key part of the feeding process of these animals.
Hunting without tentacles
Although Cassiopea most often gets its energy through photosynthesis from attached algae, they can use mucus to trap prey as recharge fuel, solving the mystery of how they get food without tentacles. (Until now these ‘water bites’ were thought to have come from separate tentacles or even younger specimens.)
The sting of the inverted jellyfish ( Cassiopea xamachana ), found in shallow waters around Florida, the Caribbean and Micronesia, is not very intense, but can leave an itchy sensation and a red rash and is enough to incapacitate an animal from little size. While the venom is not strong enough to pose a serious risk to humans, it does destroy skin cells. What these jellyfish do is lie on their back and throw globules of venom-enriched mucus into the water above their head, hence many tropical water fishermen and surfers have encountered this ‘stinging water’ on more than one occasion.
When the researchers looked at samples of jellyfish mucus under a microscope, they found “spinning balls of stinging cells” that they called casiosomes that clustered into “little spoon-shaped structures” in the creatures. Three different toxins were identified within the casiosomes after molecular analysis.
“This discovery was both a surprise and a long-awaited resolution to the mystery of the water sting,” said Cheryl Ames, a co-author of the study. “Now we can let swimmers know that water stings are caused by inverted jellyfish.” This jellyfish is frequently found in calm and protected waters, such as lagoons and mangrove forests.
The study, conducted over several years, grew out of the curiosity that some members of the research team had about the discomfort they had experienced after swimming near the apparently calm inverted jellyfish. The team described the discovery as “particularly exciting” because Cassiopea jellyfish have been known for more than 200 years, but the existence of the casiosomes was unknown until now.
Referencia: Cheryl L. Ames, Anna M. L. Klompen, Krishna Badhiwala, Kade Muffett, Abigail J. Reft, Mehr Kumar, Jennie D. Janssen, Janna N. Schultzhaus, Lauren D. Field, Megan E. Muroski, Nick Bezio, Jacob T. Robinson, Dagmar H. Leary, Paulyn Cartwright, Allen G. Collins, Gary J. Vora. Cassiosomes are stinging-cell structures in the mucus of the upside-down jellyfish Cassiopea xamachana. Communications Biology, 2020; 3 (1) DOI: 10.1038/s42003-020-0777-8
