These Jellyfish Don’t Need Tentacles to Deliver a Toxic Sting
by Hannah Knighton/Smithsonianmag.com
A mysterious burning, itchy sensation after a swim is usually the telltale sign of a jellyfish sting.
But in coastal mangroves and other subtropical ecosystems, snorkelers and swimmers have long reported a similar sensation without ever coming in contact with a jellyfish. A phenomenon called “stinging water” is to blame, but the cause is unknown.
One potential culprit is a type of jellyfish belonging to the genus Cassiopea called the upside-down jellyfish, but they are missing a key appendage normally necessary to deal a stinging blow: spaghetti-like tentacles.
Instead of a gelatinous, umbrella-shaped body with long, swaying tentacles undulating beneath as it floats through the water, Cassiopea got its common name for being the exact opposite. The soft, circular body, known as the medusa, rests on the seafloor while just a few short, tentacles float above them. Cassiopea are known to get the bulk of their energy through their symbiotic relationship with the photosynthetic algae Symbiodinium that lives within their body.
But how could the upside-down jellyfish sting something without ever coming in direct contact with their victims? These unassuming invertebrates are known to unleash plumes of mucus into the water, and…