The so-called swell shark cephaloscylum ventriosum, which is found near temperate reefs in the eastern Pacific ocean, truly lives up to its name.
When threatened - usually by a hungry sealion or larger shark - this slender, metre-long bottom-dweller slips into a crevice and inflates its body like a rubber raft.
Within seconds, the shark is twice its original size and wedged in place. And it is almost impossible to yank it out.
In open water, it adds a twist. It grabs its tail in its mouth, contorting its body into an '0* shape, and expands into a living inner tube. The bloated and awkward form complicates a predator's task: its like trying to bite an oversized balloon.
The shark swells in the same way a pufferfish does, forcefully swallowing water into an expandable stomach that has valve-like muscles. But the shark has another critical tool: a big mouth.
Larger than that of a great white, relative to its body size, this maximises the volume of fluid it can transport in a single gulp. Once peace is restored the fish opens its stomach valves, expels the extra water and quickly returns to its normal size.
Pufferfish are the most extreme bloaters, followed by the swell shark.
The swell shark's unique 'gift of puzzle' provides an additional survival benefit. This is an ambush predator, albeit an unconventional one. While it wait patiently for small fish and other seafood to swim within striking distance, it doesn't need to lunge to get lunch. It can produce enough suction with its throat to slurp up most meals just by opening its mouth.
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