Introduction The Xiphosura are members of marine chelicerates that includes a large number of extinct lineages and only four extant species in the family Limulidae, which include the horseshoe crabs. The group has hardly changed in millions of years; the modern horseshoe crabs look almost identical
Scientific classification: The subphylum Crustacea is placed in the phylum Arthropoda. The major classes in the subphylum Crustacea are the Branchiopoda (fairy shrimps, brine shrimps), Ostracoda (mussel, or seed, shrimps), Copepoda (copepods), Cirripedia (barnacles), and Malacostraca (crabs, lobster