Hoplocarida is a subclass of

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can ...

s. The only extant members are the mantis shrimp (Stomatopoda), but two other orders existed in the Palaeozoic:

Aeschronectida Aeschronectida is an extinct order of mantis shrimp-like crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulida ...

and Palaeostomatopoda.

References

Malacostraca Arthropod subclasses {{Malacostraca-stub