horseshoe crabs and extinct forms

Xiphosura is a class of marine chelicerates which includes a large number of extinct lineages and only five recent species in the family Limulidae, which include the horseshoe crabs. The group has hardly changed in millions of years; the modern horseshoe crabs look identical to prehistoric genera such as the Jurassic Mesolimulus, and are considered to be living fossils.

See Xiphura.