Profitable Wonders
Jellyfish are preposterously ancient, having flourished in the oceans for the best part of 500 million years. That’s twice as long as the earliest bony fish and insects; three times the age of the first dinosaurs.
They are thus the simplest form of multicellular life, a glob of viscous, elasticated jelly – sans brain, heart, circulation, lungs, liver, kidneys or skeletal parts. But beautiful.
‘The strangest and most delicately lovely creatures in the world,’ wrote the poetically minded, 19th-century naturalist George Romanes, ‘pulsating crystal globes, gleaming with all the colours of the rainbow.’
That delicate loveliness can be seen to brilliant effect in the famed Monterey Aquarium on the Californian coast, a kaleidoscope of ornate forms and luminescent colours undulating away in capacious, back-lit water tanks to some inner, dance-like rhythm: golden-domed with maroon-striped tentacles; toadstool-shaped, spotted white and chocolate brown. The edges of the tiny, opaque blobs pulsate with gleaming lights: light blue moons, glowing green gooseberries and orange-red flames.
Spectacle apart, the biology of jellyfish, despite their ancient lineage, has turned out to be far from simple – starting with the jelly itself (mesoglea), whose physical properties confer both buoyancy and movement. Buoyancy requires the mesoglea to have a similar density to seawater – necessitating a continuously active chemical process, pumping out heavy sulfate irons in exchange for lighter chlorine ones.
Meanwhile, the mesoglea’s natural springiness propels the jellyfish forward. Imagine a water balloon compressed around its circumference so that its contents are squeezed to either end. So, too, the jellyfish – whose mesoglea, when compressed by a circular band of muscle, alters its shape, such that it can push back on the water behind it while being sucked forward by a vortex of low
pressure in front of it. This mode of propulsion makes the jellyfish ‘the most efficient swimmer of any animal ever studied’, writes biologist Juli Berwald – utilising three times less energy than a salmon when moving a similar distance.
And they are prodigiously efficient breeders, too, facilitated by a complicated life cycle that allows for the utterly unique (and invaluable) attribute of immortality.
First, the fertilised egg develops into a larva that, affixing itself to a rock, forms a hollow tube of polyp. The polyp grows and segments transversely, like a stack of pancakes. The segments are then released as minuscule baby jellyfish (medusae), one after another, in batches of 60 at a time. This process recurs repeatedly, with a single polyp generating up to two million progeny.
The medusae mature in the usual way but, if their viability is threatened by some environmental stress or lack of food, they have the astonishing ability to revert back to polyps – as if a butterfly, rather than dying, were to change back into a caterpillar or a chicken become the egg from which it was hatched.
There is novelty, too, in how the jellyfish compensates for the absence of a coordinating brain. They could scarcely have flourished for so long without being sentient creatures capable of detecting potential prey and avoiding predators, monitoring the saltiness of their watery environment and their direction of movement within it.
Anders Garm, of the University of Copenhagen, in a series of ingenious experiments, has shown the brim of the jellyfish to be studded with 24 types of eye (or photoreceptor cells). So, rather than requiring, as do ‘higher’ animals such as ourselves, a complex brain to process and interpret visual information, each of these special-purpose eyes is attuned to detecting one or another visual cue.
Most remarkable of all, the central paradox (or enigma) of the jellyfish’s existence is that, right from the beginning all those hundreds of millions of years ago, its survival has depended on possessing that supremely sophisticated biological structure, the stinging cell (or cnidocyst) – thousands of minuscule capsules, each containing a harpoon-like dart attached to a thin, spring-like filament. When triggered, the lid of the capsule flips open, firing the harpoon with its deadly load of neurotoxic chemicals, thus immobilising its intended prey (or seeing off threatening predators).
The practicalities, described by Juli Berward, are as follows: the harpoon hits its fleshy target with a pressure similar to a bullet fired from a gun – more than a million pounds per square inch.
While a Ferrari can achieve a speed of 60mph from stationary in just three seconds (an acceleration of 3g), the acceleration of the stinging cell is 5 million g – the fastest known motion in the animal kingdom.
The jellyfish may be preposterously ancient but simple it is not.
‘The stinging cell has the fastest known motion in the animal kingdom’