Slipper Limpet, Crepidula Fornicata

This post is inspired by a poem from Isabel Galleymore which I looked at in a poetry class and fell in love with.  It’s part of her collection Significant Other which I’d highly recommend.  Whilst the poem is enjoyable by itself, knowing more about the slipper limpet heightens the pleasure and appreciation of Galleymore’s skill.

Whilst slipper limpets are found in the UK, they are a non native species that arrived from America in the 19th century.  The first live slipper limpets were found in Liverpool Bay and are likely to have hitched a ride on the back of oysters.  During the 19th century, eating oysters became fashionable in London and native stocks rapidly became depleted.  To meet demand, oysters were imported from America, along with the now invasive stowaway.

Slipper Limpets live under rocks in the intertidal zone and feed by filtering plankton from the water.  They have thin, flattened shells which has a little shelf and when flipped upside down, apparently look like a slipper hence the name.  The first half of the scientific name actually means slipper in Latin and whilst we’re thinking about the name, it’s also important to note they aren’t actually a limpet… They are instead a type of sea snail.

They live in groups of up to 12 with one stacked upon another, largest at the bottom and getting smaller as you go up the tower (or Galleymore’s “high-rise orgy“).  The base slipper limpet attaches herself to things like rocks, scallops, crabs and mussels and thus the slipper limpets live a sedentary life.  And it is always either a female or an empty shell, with the rest of the stack being male.  It is advantageous for females to be bigger than males so they can carry more eggs.  And they can lay between 10,000 and 200,000 eggs so they need plenty of space!

The male has a penis that can be as long as his body, and it needs to be; it has to extend round and under the female’s shell in order to reach her genital opening.  It is because they need to be so close that they attach to one another – imagine being stuck with your ex literally on your back until you die…

Slipper limpets are born male and will later change sex, something known as sequential hermaphrodism.  Recent research has shown that the change occurs as a result of physical contact with another male.  However, it’s not instant and doesn’t happen as a result of every contact.  The change itself takes about 60 days – or about two moon cycles – to change sex and during this time the penis shrinks and disappears and the female organs develop.

The more you learn about the slipper limpet, the more appropriate you think the scientific name is.  But whilst it would be fun to imagine an animal named for it’s sexual habits, fornicate unfortunately comes from the Latin word for arch – fornix – and refers to their arched shape.

Peak breeding occurs during May and June and most females spawn twice a year, after neap tides.  Egg capsules are brooded under the foot of the female, attached to the inside of her shell or her foot.  The young hatch as larvae after 3 to 4 weeks and will stay in larval form for about 4 to 5 weeks.  After this they will leave home.  In their early life they are able to move, slowly crawling to find a suitable site to set up home, but generally after about two years they are stuck wherever they are.  Hopefully having chosen the perfect spot, given they live up to 10 years.  If they settle alone, they will turn female and become the base slipper limpet.  Alternatively, they will join an existing chain and wait their turn.

Scientists have been looking at the Slipper Limpet to see if it has any medical benefits for us and hemocyanin – the same chemical that makes the blood of horseshoe crabs and octopuses blue – has been found in their blood and is effective in treating breast and bladder cancer.  Their tough fleshy food may also have uses for human medicine.  Collagen from it can be used in regenerative medicine, such as advanced wound care and bone and nerve repair.  Whilst collagen is found in virtually every living organism, the collagen from the slipper limpets is stable in the same range as human collagen and thus provides an alternative source – at present collagen from cows and pigs is used.

Returning to the poem, I am in awe of Galleymore’s ability to make us stop and think twice about this seemingly dull, drab, slightly gnarled looking creature.  Without her poem, I wouldn’t know about the slipper limpet and I certainly wouldn’t have had so many conversations about it.


She sells sea shells…

“Since prehistoric times, we have found shells, picked them up and looked at them in wonder.  People have contemplated the seashells’ beautiful shapes and the mysterious ocean realm they come from and turned them into great treasures…. Shells can offer us insights into the minds of our distant ancestors, and teach us about beauty and form and the curiosities of life on earth”
– Helen Scales

Seashells are beautiful, intriguing and wonderful.  They ask us to pause, to admire, to imagine.  We turn them over in our hands.  We hold them to our ears hoping to hear the waves of the sea, the ghost of the inhabitant recollecting their life in the ocean.  We admire these messengers from the deep but despite this admiration, I think we still overlook them or underestimate them.  These are creatures which can turn seawater into mesmerising shells.  And what an amazingly diverse array of shells they make with their twists and spirals and patterns all utilising beautiful mathematical principles.

For the shell maker, the shell provides protection, a home and a safe place for eggs and babies to develop.  They are used in defence – limpets stamp down on starfish limbs as they try to attack. The chambered nautilus is one example of using the shell as a flotation device.  And perhaps most creatively, the Heart Cockles use their shell as a greenhouse.  They cultivate photosynthetic microbes inside their shell and their shells have a small transparent window to let the light in.  The microbes have a safe place to live and the cockles have a free meal.


It’s not just shellfish that use shells.  They are eaten by other sea creatures of course, and by humans, but a less obvious but equally important role of shellfish is in building ecosystems.  Shellfish such as oysters create beds and banks which become a sanctuary for plants and animals.  These beds also protect our coastlines from storms and erosion and clean the water for us as well.

We have used shell makers to advance medicine and we have used their shells for thousands of years as tools such as knives, anvils and fish hooks.  We have even ground their shells into powder to add to livestock food as a source of calcium.

Shells of course have long been used as decoration and symbols.  The seashell is an emblem of sexuality, of birth and of death.  The cowrie shell could be said to have a likeness to the vulva, when viewed from one angle, and a pregnant belly from another angle.  The waters where shells are found is life giving and by extension the shells have come to represent the protective womb.  Shells are also associated with the virgin mary and hence with a pure fertility.

When it comes to death, shells have been placed next to the deceased, perhaps as signs of wealth but also as decoration and the Seneca people believed that shells in the grave could purify the decaying flesh and allow the soul to enter the spirit world.

The conch, instead of purifying, has a place in history alongside war and power.  Whilst used and abused by children in Lord of the Flies, this association goes back much longer.  Tales from ancient India describe heroes carrying white conch shells in war.  A conch called Panchajanva (which means having control over the five classes of being) is one of the emblems of Vishnu.  And conches were blown, like trumpets, to proclaim battle, adding to the symbolism of power, authority and sovereignty.

However, this power need not be associated with war, like all power it is what you do with it that matters.  For centuries, the wail of conch trumpets has echoed across the peaks of the Himalayas, calling Tibetan Buddhist monks to prayer.  They are carried hundreds of miles from the Indian Ocean up to the mountains where they are carved and decorated.  Shell music is then played by the monks into the skies to ward off storms and evil spirits.

In Candomblé, an Afro-Brazilian religion, shells are used to communicate with the gods as well as for offerings and in rituals.  Shells have also been used as amulets and feature in a number of creation myths.

The Seneca people believed that to look through a shell is to gaze back to the beginning of time.  I love this idea, especially when you combine it with listening to the shell to hear the sea.  Both concepts feel like the shells are bringing us messages from a world very different to ours, very far away from us.

Shells have captured the imaginations of humans and have been a mirror for reflection:

“Through imaginative thinking I have become more aware that shells are “sublime subjects of contemplation” for the mind…I have come to appreciate that shells, specifically sea-shells, “stand out from the usual disorder that characterises most perceptible things.  They are privileged forms that are more intelligible for the eye, even though more mysterious for the mind” or psyche.”
– Dr Rex Van Vuuren, Much in a Little: Reflections on the Gift of a SeaShell

Later in the paper, a quote from a client is shared which provides food for thought:

Delicate and fragile yet endowed with an inner strength that survived and defied the sea storms of life.  The uniqueness of each shell touched me.  There are so many shells in the ocean but not one like me.

The shell metaphor extends and the client sees herself as shelled in, as having withdrawn into her shell and as her therapeutic journey being one of emerging from her shell.  The shell, as a mirror, has given her space to think and clarity over her situation.  It allows her to reflect and to move towards understandings.  As the therapist writes:

A slow and unhurried imaginative consideration of the shell allows the client to move toward a realisation and unification of the self, body and soul, in ways that no therapist could possibly emulate.

But what we see when we reflect on seashells is not always pretty.  A particularly low point for the human shell relationship was during the slave trade.

Money cowrie shells were gathered in the Maldives, then exchanged for rice and cloth in India.  From here they were taken by Arab traders to Africa where they were used as money.  This had been going on for a long time and then, at some stage in our dark history, Europeans entered the equation and began using shells to buy people.  In the 1680s, a slave cost about 10,000 shells but by 1770s the price had increased to 150,000 shells.  At the peak of the slave trade, British fleets imported about 40 million cowries into west Africa a year.

Today, shells are sold as curios and souvenirs around the world, a nice token to remember our day.  But these too have a dark side.  Rarely are these shells found on beaches, instead they are taken from living animals as the quality of the shell is better.  These creatures are collected on an industrial scale, killed and have their shells removed just so that we can take home a trinket from our time by the sea.

And the shell you buy probably doesn’t belong to a creature that lives in the area.  Shells are imported, possibly even from the opposite side of the world – the Philippines are a major exporter of shells, trading in over 1000 mollusc species.  As well as the impact on the individual mollusc, there is impact on their populations and the harvesting process can damage habitats and other organisms.

Shells tell us stories of humanity, of our ingenuity and tool building, of our religions and beliefs, of our wars and of our darkest days.  Next time you hold a shell in the palm of your hand, feel the weight of our history, our present and our future.