Bradoriids are small marine arthropods with a bivalved carapace, and were globally distributed, forming a significant portion of the Cambrian and early Ordovician soft-bodied communities.
Whilst the Bradoriida were traditionally considered as relatives of the modern bivalved arthropod group Ostracoda, the anatomy of their appendages does not support such a relationship; neither are they related to the Cambrian bivalved arthopod group Phosphatocopida. Rather, they are most probably related to the Eucrustacea at a stem-group level. Occurrence
Bradoriida are geographically widespread, and occur in the fossil record shortly before the earliest trilobite fossils. Their taxonomic composition broadly reflects two geographical provinces ("European" and "4A", i.e. America, Asia, Australia, Antarctica) which approximately mirror trilobite provinces, with the 4A area representing warmer waters closer to the palaeoequator.
Reference: Hou et al. (2010)