Branchiura (Fish Lice) is a subclass of oligostracan crustaceans. There are 158 species of Fish Lice, in 4 genera and 1 family. This subclass has been around since the wordian age.
Definition: The number of fossil occurrences in the Paleobiology Database (https://paleobiodb.org) that are identified as belonging to a particular taxon or any of its subtaxa.