Spirals in Time: The Secret Life and Curious Afterlife of Seashells by Helen Scales

Reviewed by Annabel

There are large numbers of popular science books written about particle physics, space and the periodic table, ditto for medicine and the mind. There are fewer books about biology and the natural world (unless David Attenborough has a new TV series), and fewer still specialising in single groups of less cuddly animals, flag-bearers for evolution or endangered species. So, to discover an enchanting and elucidating book all about seashells was an absolute delight.

Helen Scales is a marine biologist. Her first book, Poseidon’s Steed, was about seahorses; those special little sea creatures where the males bear the young. In it, she not only wrote about the biology of these creatures, but also their place in culture and mythology. In Spirals in Time, she has turned her interests into a much larger phylum – that of seashell-making molluscs – and similarly gives us much more than a purely biological appreciation of them.

Her prologue tells how, ‘Since prehistoric times, we have found shells, picked them up and looked at them in wonder.’ Everyone loves seashells, and she recounts her days as a child on the beach in Cornwall decorating sand castles with shells – the sandy beach of Trebarwith Strand with its many rock pools being a favourite (mine too). The fascination with sealife never dimmed and she went on to get her dive certificate and study marine biology.

Introductions made, we move on to meet the molluscs. From snails to octopuses, they are a varied lot and not all shell-making. She gives us a brief tour of the groups and how they move around in many different ways. It is here we learn that mollusc slime is thixotropic – but Scales doesn’t use that word, instead she clearly explains that when the mollusc presses down on the slime ‘it turns into a free-flowing liquid. This reduces the friction on part of the foot and allows the mollusc to push forwards.’ She also discusses all the various uses of the creatures’ mantles – from shell-making to helping propel the swimming creatures — and we meet the Grimpoteuthis, common name Dumbo Octopus, whose mantle resembles giant flapping ears.

Another important distinguishing characteristic of a mollusc is that it only ever makes a single shell, unlike crustaceans for instance. They just keep expanding the shell by adding more, so ‘the pointy tip or innermost whorl is the mollusc’s juvenile shell.’ We take some time to look at the geometry of shells – and here is the only bit of maths in the book which explains (with helpful diagrams) the different axes and parameters affecting the growth of spiral shells, as exemplified by the chambered nautilus, whose shell is a logarithmic spiral similar to the golden ratio.

This is all fascinating biology, but Scales moves on to talk about some cultural aspects of seashells – the money cowrie was for many years used in place of coins and many people became very rich harvesting millions of the little shells and importing them to where they were used as currency.

Perhaps the most entertaining chapter discusses the place of shells in the world of fashion, and the strange and rare fabric that is known as sea-silk in particular. Sea-silk was (and is) harvested from the fibrous beards or byssus of giant mussels known as Pinna Nobilis or Noble Pen shells. The pinna half bury themselves in the seabed, using the fibres that grow from their point much like tree roots to pin them down. Around 1800, decorative trims or small purses made of the spun byssus threads were much prized – Nelson gave Lady Hamilton a pair of gloves. The shells grew in the Mediterranean near Sardinia, but not in large quantities even then, so only handfuls of the byssus fibres could ever be harvested at any time, and uprooting the shells will kill most of them. They are protected now.

Other chapters cover subjects from the contemporary, like the project trying to re-establish an oyster business in the Mumbles near Swansea and the scientists trying to analyse the varied and often deadly toxins produced by cone shells, to the ancient – looking at ammonites and argonauts (shelled octopuses). Scales also looks at the seashell collectors – the Natural History museum has a huge Victorian collection thanks to Hugh Cuming, the owner of a shoe-business who escaped to become a naturalist.

We couldn’t have a book about seashells without covering the subject of ocean acidification – a by-product of producing more CO2. Seashells are formed mainly from calcium carbonate like limestone which is eaten away by acid rain. More CO2 dissolving in the oceans makes the water more acid, and shell-making more difficult – leading to thinner or deformed shells and disappearing corals too.

The book concludes with a cautionary note about shell collecting – the majority of shells sold at the seaside are imported, the creatures are killed for their shells — and a glossary completes things.

My only quibble with this book is that I would have liked more pictures – there is one colour photo selection, plus line drawing headers for each chapter; illustrations and diagrams are otherwise sparse. However, this is more than made up for by the quality of Scales’ writing. She tells her stories with such enthusiasm for the subject, explaining clearly with a great sense of humour, that she draws vivid pictures of these marvellous creatures in words. I absolutely loved the way she introduced all the stories that contrast with the biology into the text, making this a book to recommend to a far wider audience than just those who like the natural world.