Hermit crabs have a lot of flexibility in the shells they use, and different kinds of species have made shells over the millennia. So it’s surprising that we find hermits in shells of species that no longer exist, like ammonites:
Here’s a reconstruction of what that might have looked like:
The shells looks a little bigger in proportion to the crab that modern snail shells. But any ol’ port in a storm.
Fraaije RHB. 2003. The oldest in situ hermit crab from the Lower Cretaceous of Speeton, UK. Palaeontology 46(1): 53–57. http://dx.doi.org/10.1111/1475-4983.00286
Hat tip to Tim Ziegler (here) and Louise Johnson on Twitter.