It’s not a fish, a whale or a jellyfish – the giant siphonophore (Praya dubia) is the unlikely giant of the underwater world.

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How long is a Praya dubia?

The giant siphonophore grows to more than 40m and lives in cold waters at depths of 50–200m. It is a colonial animal, which means it’s actually a long chain of individuals. Each one has a dedicated role – some sting and capture food, others digest and spread the nutrition throughout the colony, while the remainder are responsible for reproduction.

These creatures form a long, pliable stem that trails behind two much larger bodies that are specially adapted for swimming, pulsing rhythmically and slowly, pulling the smaller animals through the water.

How does the Praya dubia catch its prey?

A thin, gauzy curtain of stinging tentacles that can reach two metres in length hangs from the predatory cells. Any passing prey that comes into contact with these appendages is rapidly hauled up to the feeding polyps and devoured in an instant.

Though Praya is the longest and one of the most abundant predators in the ocean, it is surprisingly only as thick as a coin. So the female blue whale still wins when it comes to sheer bulk. Adrian Barnett

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Main image: an illustration of praya dubia © Alzinous, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons

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