Spirals in Time: The Secret Life and Curious Afterlife of Seashells (28 page)

Next, she tried breaking off small chunks of shell. After being inflicted with this new level of damage, an argonaut would spend hours sorting through bits and pieces on the aquarium floor, testing out shell fragments to find ones that were a perfect fit for the gaps; it would then glue the chosen pieces in place on its shell to complete the broken jigsaw puzzle.

The discovery that argonauts are equipped with these expert shell-fixing skills lent more support to Jeanne’s argument that they do indeed make their own shells and don’t simply steal them from other animals. But there was still one final part of the picture left to find: Jeanne needed to catch an argonaut in the act of actually making a shell.

Contrary to the reports made by Giuseppe Saverio Poli, Jeanne saw no sign of a shell when she examined unhatched argonaut eggs. However, she carefully watched as they hatched and grew up, and saw that when the young animals reached the size of a little fingernail, around nine millimetres (a third of an inch) across, they began to build their hard outer covering. As the argonauts got bigger, so did their shells.

Thanks to Jeanne’s extensive research, there was no longer any doubt that argonauts do indeed make their own shells, and that they do it in a completely different way from all the other molluscs. Instead of secreting a shell with their mantle, argonauts have shell-making glands at the end of those two arms that she observed repairing breakages; these are spread out into broad membranes (the very same ‘sails’ that Aristotle imagined argonauts unfurled to propel themselves over the seas).

All of these discoveries could have been lost and forgotten had Jeanne not kept up with her correspondence, and been
good at publishing her findings. When Jeanne and James Power decided to leave Sicily and live in London, then Paris, they travelled overland. Meanwhile Jeanne arranged for the bulk of her papers and research equipment to be sent on afterwards by sea; everything was packed up and loaded onto a sailing ship bound for London. A short way into the voyage, off the French coast, disaster struck. The ship sailed into a storm and sank, sending Jeanne’s treasured collections into the ocean depths (the kind of romanticised disaster that rarely strikes scientists today, but perhaps a reminder to do regular data backups – the modern equivalent of avoiding a shipwreck).

Jeanne’s findings live on in pages of letters she wrote to Richard Owen at London’s Natural History Museum, and in the various papers and studies presented in scientific journals. However, her legacy as an early female scientist has faded and she is little remembered for her achievements. Her dedicated research saw her elected as a rare female member of many scientific institutions in Italy, France, Belgium and England, including a corresponding member of the Zoological Society of London. Few people nowadays have heard of the lady who spent years watching, probing and asking questions about this obscure but captivating group of animals.

In the years since Jeanne Power conducted her studies in Sicily, knowledge of argonauts and their way of life has continued to grow. We know they feed on various other animals that live up in the water column, including fish, jellyfish and sea butterflies; we know the females make their shells by laying down material on the inside and outside; we know that no two argonaut shells are exactly the same because of the way they patch them up (this makes it extremely difficult to identify species based on their shells alone); we know that when argonauts meet they sometimes
cling to each other and form rafts. No one really knows why they do this, but it could explain why hundreds of them sometimes strand together on beaches.

We also know a lot more about the argonauts’ strange sex lives. Throughout her studies, Jeanne noted that she only ever found egg-producing female argonauts. Where were the sperm-making males? She was the first scientist to suggest that the worm-like objects found stuck to female argonauts could be something to do with the males. When Georges Cuvier originally spotted this peculiar appendage he identified it as a parasitic worm, and in 1829 named it
Hectocotylus
. Much later, following Jeanne’s suspicions, it transpired that these were not in fact worms at all but important mementos left behind by inconspicuous males.

Without doubt the less impressive of the sexes, male argonauts can be 12 times smaller and weigh 600 times less than females; they barely reach the size of a peanut. The males don’t make shells, but they do have an impressive trick up their sleeves. One of their eight arms is specially modified into a sperm-delivery organ. In other words, they have a penis on the end of an arm. What’s more, the male argonaut’s penis is detachable.

The word
hectocotylus
is now used for the arms of many male octopuses and squid that dole out packets of sperm to females. Amid a grabby clinch of arms and tentacles, the male will reach into the female’s body (in argonauts there is a cavity under the mantle; in other octopuses the male pokes into the female’s body just under her eyes). He detaches his wriggling, sperm-laden limb, which clamps on to her with suckers. Female argonauts will often collect and carry around the offerings from several males at once.

After dropping their penis some male cephalopods will grow a new one, but not male argonauts. They only get one shot. Their arm drops off, hopefully stuck to a receptive female, and shortly afterwards they die. Female argonauts, on the other hand, keep going and unlike their octopus cousins
they can rear many clutches of young over the course of their lifetimes. Most mother octopuses deposit their eggs inside caves and crevices on the seabed. They will usually stick around to watch over their offspring, to fend off predators and keep their broods well oxygenated with wafts of clean water. A deep sea octopus has recently been seen in the Monterey Canyon off the Californian coast guarding her eggs for 53 months, by far the longest period of egg-brooding ever seen in any animal. After all that time, and possibly even longer, she will most probably die, as most female octopuses do, after their single, tremendous reproductive effort.

Living up in open water, where there are no caves to lay their eggs, female argonauts make their own portable, protective nooks to nurture their young. But their shells aren’t just brood chambers, they do other things besides. Watching argonauts for brief periods in aquariums, some scientists have argued that air trapped inside their shells is nothing but a nuisance, making it difficult to steer and stranding the animals at the water surface. Others have entertained the possibility that argonauts wilfully manipulate air bubbles inside their shells, and use them like underwater blimps.

It wasn’t until 2010 that this matter was put to rest, when
Julian Finn
from Museum Victoria in Melbourne, Australia paid a visit to the Sea of Japan. Three female argonauts were caught in fishing nets offshore and brought into Okidomari Harbour, where Julian climbed into his scuba gear and carefully took the argonauts with him down beneath the waves. He emptied all the air out of their shells and released them, one at a time, and watched while all of the argonauts performed the exact same routine.

First the argonauts zipped straight upwards, squirting themselves along using jet propulsion. Arriving at the surface, they squeezed out an especially vigorous jet of water that let them bob up and draw as much air into their shells as possible. Next, the argonauts repositioned their funnels and jetted back down, pushing themselves deeper and deeper.
Being essentially open to the water and not fully sealed off, the air bubbles inside their shells were squashed, and shrank as the argonauts swam down and the pressure around them increased. Eventually the argonauts reached a depth where the air volume inside their shells cancelled its weight and the animals became neutrally buoyant, and therefore effectively weightless: they didn’t sink or float but hovered in the water column. On reaching that magic depth, between seven and eight metres (about 25 feet) down, the argonauts scooted off horizontally at high speed, swiftly outswimming Julian and his diving assistants.

Watching them disappear from sight, Julian was certain that the argonauts were deliberately using air as a tool to help them swim efficiently at a shallow depth beneath the sea surface, where they are less likely to get knocked around by waves or picked off by a hungry seabird from above. It would explain why the exhausted argonaut brought to the Cabrillo Marine Aquarium needed a helping hand to fill up her shell at the surface and gain some much-needed buoyancy.

Modern genetic studies confirm that the paper and chambered nautiluses are only distant cousins. Argonauts are without doubt octopuses, members of the coleoid lineage alongside cuttlefish and squid. And the nautiluses are the last few survivors of an ancient cephalopod pedigree, the nautilids, that have been doing their own thing for more than 400 million years.

After all that time, these two groups of animals are living proof that having a gas-filled shell is an efficient way of moving through the oceans. They may not be as agile and swift as some of their cephalopod relations, but they are certainly not as primitive or outdated as the label ‘living fossil’ implies. And we now know for sure that when nautiluses die and leave their shells behind, argonauts don’t pick them up and use them.

But humans do.

CHAPTER EIGHT

Hunting for Treasures

I
n the silver gallery at the Victoria and Albert Museum in London – among the hundreds of gleaming goblets, crowns, platters and spoons – is a nautilus cup. It is made from the shell of a chambered nautilus that lived around 400 years ago, and since its death has been transformed.

Most of the shell’s ochre stripes have been scraped carefully away to reveal the gleaming mother-of-pearl underneath; glimpses of tiger markings have been left here and there, woven into a swirling design carved across its surface. On the shiny parts a gathering of animals are engraved in fine detail: spiders, wasps, moths and ladybirds. The shell is cradled in a silver gilt mount decorated in enamelled flowers and tendrils, with more insects clambering through them.

The nautilus cup was made in the Netherlands in around 1620. It was probably never actually used as a vessel but would have been put on display in a cabinet of curiosities. Chambered nautiluses were considered to be masterpieces of nature, but they were still something that man could improve on. Just as Noble Pen Shells were displayed alongside articles woven from sea-silk, complete nautilus shells were arranged next to crafted nautilus cups, encouraging viewers to contemplate nature’s raw materials and the skill of the artisan who enhanced the shell’s beauty through carving and engraving.

The museum’s collection includes several more nautilus cups. The Burghley Nef is a French sixteenth-century salt cellar, crafted from a nautilus shell into a medieval sailing ship propped up on a silver mermaid; there is a sixteenth-century cup from England with a golden sea monster opening its ferocious jaws and poised to engulf the tiny figure of Jonah (the original nautilus shell was lost and is now replaced with a silver facsimile); a Polish nautilus shell clasped in an extravagant gold mount and covered with engraved glass and gemstones is dated to 1770.

All of these nautilus shells were probably imported from Indonesia by Dutch merchants aboard some of the same fleets that carried billions of Money Cowries from the Maldives to exchange for slaves in West Africa. These global trade routes supplied an enormous demand for exotic objects from faraway places, including many varieties of seashell.

In auction houses across Europe throughout the eighteenth century, shell mania took hold as rich collectors paid exorbitant prices for rare and beautiful specimens. By the beginning of the nineteenth century, cabinets of curiosities were gradually being replaced by more orderly, systematic collections of natural history objects kept by people who knew what they were looking at. While most collectors didn’t stray further than the auction rooms, there
were those who aspired to go on much greater adventures. At around the time that Jeanne Power was embarking on her studies of argonauts and their shells, another unsung pioneer of natural history was setting out to pursue an eccentric dream. Hugh Cuming spent years on a series of intrepid adventures on the high seas, risking his life in far-flung lands, and all because he wanted to collect more seashells than anyone ever had before. He brought thousands of shells back from his global journeys; they redefined the boundaries of species diversity in the natural world.