A warning has been issued to bathers after a large number of Portuguese Man 'o War, Physalia physalis, were found washed up on Sennen and Portheras Cove beaches near Penzance in west Cornwall on Sunday 6 October 2019. People are being urged to be
wary of both the animals themselves, and any detached tentacles, as the
venom of the species is particularly potent, and can occasionally kill
Humans, though children and pets are thought to be more at risk than
adults.
Portuguese Man o' War are colonial Siphonophores only distantly related
to true Jellyfish, Scyphozoa, though commonly referred to as such. Their
bodies are made up of thousands of individual zooids, each with their
own sting, tentacles and digestive system. New zooids are formed by
budding from other members of the colony, but remain attached to these
to form a single colony. Each year a generation of specialist sexual
zooids (gonozoids) is produced which produce eggs and sperm, with
fertilised eggs going on to form new colonies. These animals are
anchored to the sea surface by a highly modified zooid which forms an
air sack, filled with a mixture of carbon monoxide defused from the
zooid and nitrogen, oxygen and argon from the atmosphere, which are
brought into the sack through osmosis.
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