Since the Ordovician period, there have been uncountable numbers of you, with many distinct shapes and subspecies, hunting through all the world’s oceans, and leaving excellent fossils, as so many shelled creatures tend to do.

You must be tough: you have survived, virtually unchanged, several massive extinction events which took out the majority of all the living species each time.

However, most of you have died out since the Triassic, and the few remaining species are often referred to as living fossils. But - you are still around, hanging grimly on: you are a Horseshoe Crab.