Italian coasts and deep‑sea Argentine waters reveal dangerous and giant jellyfish

In Italy’s coastal waters several jellyfish species pose varying risks to swimmers. The highly stinging Pelagia noctiluca, commonly pink‑violet and 5‑10 cm wide, is the most feared. Other frequent visitors include the moderately irritating Rhizostoma pulmo, the almost harmless Aurelia aurita, the cubomedusa Carybdea marsupialis, and the extremely dangerous Physalia physalis with its long tentacles.

Identification advice stresses colour, tentacle length and shape: bright hues and thin, long tentacles usually indicate higher toxicity, while short, fleshy tentacles are less hazardous.

In the deep Argentine Sea, researchers using a remotely operated vehicle recorded a specimen of the giant Stygiomedusa gigantea, nicknamed the “ghost jellyfish”. The medusa measured about 11 metres—roughly the length of a bus—with a bell up to one metre in diameter and four ribbon‑like arms extending over ten metres. It lacks stinging tentacles, feeding by ensnaring fish and plankton. The finding adds to the scant global sightings of this millennial‑old deep‑sea species, which inhabits depths of 1,000‑3,000 metres.