What are these shells?

We visited Bournemouth at the end of October and my daughter and nephew found these unusual-looking shells on the beach. They brought them to show me and asked if I knew what they were.

From the top, they looked like several shells stuck together but, from underneath, they looked like a single creature. They were quite heavy and I could see something dark and squidgy inside, so I knew there were creatures living in the shells. But I had never seen anything like this before (even though I used to live near the sea)!

We put them back where we found them and I promised to find out more about them when we got home. So, what are these shells and why do they look so unusual?

It was tricky to find out about these shells and the creatures that live inside because I didn’t know what they were called. I wondered if they might be a kind of sea snail but the shells looked the wrong sort of shape. The children thought the shells looked a bit like clenched fists but none of my reference books gave any useful information to help us identify them.

I asked a friend at work, who knows about a lot of different animals, but she didn’t know what they were either. However, she suggested trying iSpot – a nature detective website that can help to identify plants and animals and other living things from photos that people have taken. I couldn’t see anything that looked quite right, so I sent my photo to some other scientist friends to ask for help. And very soon, I got an answer!

It turns out, they are ‘common slipper shells‘ or slipper limpets and they are a kind of sea snail. As part of their lifecycle, they join together in a pile to reproduce, which gives them their unusual appearance. They are a non-native species, which means they came to England from another country but now they can be found living on British beaches. Some people like to eat slipper limpets (but they don’t sound very delicious to me)!

Have you ever found an unusual shell at the beach and were you able to work out what kind of creature lived inside?