Phyllocarid Brachiocaris pretiosa from Utah

Description: This Phyllocarid arthropod is known as Branchiocaris pretiosa. The affinity of Branchiocaris is disputed. Some rank it as being within a stem group of euarthropods, and others as a primitive branchiopod crustacean within the arthropod crown group, the latter being the most accepted classification.

Branchiocaris have a large carapace that protects the anterior part of the body. This carapace structure hinged along the dorsal edge in the same manner as a bivalve. Usually only the carapace is fossilized, and only very rarely are the soft parts preserved in as in this case in lagerstatte fossil sites.

The taxon is also known from the Burgess Shale of British Columbia, where it is rare, while another member of the genus (Branchiocaris yunnanensishas) is described from the Chengjiang Biota.

Resser (1929) named the genus Protocaris and classified it as a phyllocarid crustacean, but other workers later considered it more closely related to trilobites. Four decades later Briggs (1976) erected the new genus Branchiocaris, prefering a stem arthropod status. Bergström (1997) later placed Branchiocaris was a calmanostracan branchiopod, while other's phylogenetic analyses placed it close to Marrella (Briggs, Fortey and Wills, 1992). Budd (2008) argued Branchiocaris to be a stem euarthropod, belonging to a clade also containing Odaraia, Fuxianhuia, Perspicaris and Canadaspis. Thus, Brachiocaris continues its enigmatic legacy.

The subclass Phyllocarida contains three orders, one extant (Leptostraca, classified as a Malacostracan), and two extinct (Hymenostraca and Archaeostraca).

Also See: Utah Cambrian Explosion Fossils Pseudoarctolepis Phyllocarid Fossil from Wheeler Formation

References:
Briggs, DE. 1976. The arthropod Branchiocaris n. gen. Middle Cambrian, Burgess Shale, British Columbia. Geological Survey of Canada Bulletin, 264: 1-29.
Briggs, DE. FORTEY, MA., and WILLS, MA. 1992. Morphological disparity in the Cambrian. Science, 256: 1670-3.
Budd, GE. 2008. Head structures in upper stem-group euarthropods. Palaeontology, 51: 561-573.