Mesozoic crustaceans

Phyllocarida is a subclass of crustaceans, comprising the extant order Leptostraca and the extinct orders Hymenostraca and Archaeostraca. This clade of marine crustaceans diversified extensively during the Ordovician. left|thumb|Undescribed fossil of a very large phyllocarid from the Yukon ([[Devonian)]]