New species of Liostracina Monke, 1903 (Trilobita, Cambrian) from Yunnan, China: complete holaspid exoskeleton and implications for higher level classification

The trilobite Liostracina has been recognized as important in taxonomic and stratigraphic studies for more than a century. Until now, the genus Liostracina and family Liostracinidae have been known from only incomplete holaspid material, a degree 2 meraspis, and protaspides. A new locality in the Longha Formation (Cambrian: Guzhangian) of southeastern Yunnan, China, yields a rich collection of articulated holaspid exoskeletons and disarticulated sclerites of a new species, Liostracina fuluensis n. sp. These specimens reveal thoracic and ventral morphology that was previously unknown for Liostracina; they demonstrate that it has a rostral plate plus rostral and connective sutures, rather than a ventral median suture on the cephalic doublure. This confirms a natant hypostomal condition for the genus. Holaspid exoskeletal features, combined with evidence of a non-asaphoid-type protaspis, indicate that Liostracina is neither a primitive trinucleoid nor a primitive asaphoid. The family Liostracinidae is excluded from the superfamily Trinucleoidea and the order Trinucleida and reassigned to the order Ptychopariida. UUID: http://zoobank.org/48dcbe31-e25d-4657-8441-732d5ea2b49d