Swimmers who feel “stinging water” near mangrove forests may be getting zapped by jellyfish snot.
A species known as the upside-down jellyfish (Cassiopea xamachana) can sting other creatures without ever making direct contact. Instead, the jellyfish releases mucus filled with clusters of stinging cells typically found on jellyfish tentacles, researchers report February 13 in Communications Biology. The study provides the first explanation for why handling or swimming near upside-down jellyfish can cause a prickling or burning sensation (SN: 9/1/15).
The stinging cells are coated on tiny mobile blobs called cassiosomes within the mucus that “zoom around like a Roomba zapping brine shrimp” in a lab dish, says Cheryl Ames, a marine biologist at Tohoku University in Sendai, Japan. When brine shrimp came into contact with a cassiosome, the shrimp were quickly paralyzed and killed.
C. xamachana is unusual among jellyfish in that the animal rests belly up in groups on the seafloor, which lets photosynthetic algae living in its tissues produce nutrients that benefit both organisms (SN: 8/22/14). Upside-down jellyfish are found in tropical waters near coastal mangrove forests.
It’s unclear how the jellyfish use their stinging snot in the wild, but the mucus could be part of their feeding strategy, or could be used in defense against predators. In the lab, when upside-down jellyfish were agitated or eating, they released clouds of mucus.
Microscopic views showed that the mucus was filled with what Ames calls a “spider web of things,” including food particles and cassiosomes moving around. Puzzled, the researchers searched through research on jellyfish and found a 1908 book in which zoologist Henry Farnham Perkins suggested that the cell clusters could be parasites, after his theory that they were embryos was proven wrong. Perkins wrote that he was “still quite in the dark as to the nature of these curious bits of animal life.”
The researchers found, however, that cassiosomes are hollow cellular masses lined on the outside with stinging nematocyst cells, and are also covered in bristlelike cells that help them move within mucus. Separated from the snot, cassiosomes stayed mobile for up to 10 days.