Hidden Britain
Meet a furry sea mouse that can reflect light
Walk a storm-blown strand-line and mingled with the flotsam and jetsam of humanity you’ll find a tangle of natural treasures. If you’re lucky, these will include a strange creature called the sea mouse, Aphrodita aculeata. It’s a psychedelic fuzz of fur and spine, and can look like both something and nothing.
From one angle it resembles a sandy fur-ball. But from another, it catches the light and your eye. Pop it in some seawater and it takes on a completely new vibrance. It becomes a splash of fibre-optic brilliance.
The sea mouse simply doesn’t conform to what you might expect a ‘worm’ to be. Far from being a slim tube it is quite chunky: up to 20cm long and 5cm wide. The body is covered in a velveteen pelage, and its perimeter is trimmed with a wide skirt of long glassy hairs (setae) amongst which are embedded a palisade of much thicker, stouter spines, making the creature quite prickly.
Turn the worm and you’ll get a hint as to its place in the animal kingdom. It is a kind of segmented (annelid) worm, with its body divided up into sections. Each has a pair of fleshy ‘feet’ called parapodia, complete with a bundle of more spines at the tip. The sea mouse uses these as it ploughs through the seabed sediments, as deep as 3,000m, where it hunts other worms, molluscs and crustaceans. Most of the sea mice washed up are dead, or lethargic at best, but if you do place one in a clear-sided vessel of seawater, you will hopefully observe its real magic. Natural light falling on the worm’s veil of fluff creates a kaleidoscopic rainbow of colour – a phenomena termed pseudobirefringence. This chromatic shimmering of blues, reds, greens and yellows seems to emanate from the finer strands, while the thicker spines glow ember-red, making for a garish opulence rare in a creature of the deep. hollow h hexagonal tubes, which ru un parallel to the length of the bristle. b A cross-section therefore lo ooks a little like a honeycomb.
When light hits this precise matrix m of tubes, it splits and re eflects back those portions in n a specific part of the light s pectrum. Amazingly, this s tructure is very similar to th he artificial structures being developed d by physicists in th he exciting field of photonic c communications, which uses li ight instead of electricity in n telecommunication and computing. c For this we need to be b able to amplify and control photons. p The sea mouse has been b doing this all along.
Not only did this worm get th here first, it exhibits almost 100 per p cent reflectivity – much better th han anything our technology has come c up with. What’s more, it achieves a this using nothing more th han a simple arrangement of hexagonal h crystal-like structures exuded e from its skin. But how does d the worm benefit?
One theory is that the light s how deters other predators in n the dimpsy darkness of the underwater u world. If our worm used u normal pigmented colours, much m of the light hitting its fur would w simply become absorbed. By B deploying photonics th he worm overcomes these li imitations on the seabed.