Avast! It's a gas-filled blob with a sting in the tail



APART from its wondrously alien look, the coolest thing about the Portuguese man-of-war is that it is not an individual animal at all. Nor is it a jellyfish.

It is a siphonophore – an entity formed of a colony of tiny animals called zooids. These creatures are so closely integrated with one another that they can't survive on their own. The zooids form at least three specialised types of polyp. There are polyps dedicated to digestion and to reproduction. Then there's the dangerous type – the tentacles that can trail up to 50 metres below the surface, making it one of the longest "animals" on Earth. These tendrils carry venom that can kill small animals, like the unlucky fish in the photo. Although desperately painful for humans, the sting doesn't usually kill us.

Above the water, the most visible part of the siphonophore is the gas-filled bladder, said to resemble an 18th-century Portuguese warship (to me, the shot below looks more like Godzilla emerging from the ocean). The bladder contains carbon monoxide, generated from a gas gland. It can be deflated in the event of a turtle attack, allowing the colony to sink out of harm's way.

Marine-life photographer Norbert Wu, based in Pacific Grove, California, took this shot in Bermuda. While the man-of-war favours tropical and subtropical waters, unusual currents can bring it to temperate shores.



( This article appeared in print under the headline "Shiver me tendrils")