Jellyfish snot can sting swimmers who never touch the animal

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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. 

jellyfish mucus and magnified cassiosomes
Upside-down jellyfish mucus (cloudy material in left image) contains cellular blobs called cassiosomes (right; 100x magnification), lined on the outside with stinging cells. The yellow bits inside the cassiosomes are photosynthetic algae.From left: Allen Collins, C. Ames; C. Ames, Anna Klompen

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.

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