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Taxonomy according to Fossilworks.org. Isoxys auritus was originally erected as Cymbia auritus Jiang, 1982 on the basis of a single specimen from the Lower Cambrian Helinpu Formation, eastern Yunnan, China, and was synonymized with Isoxys by Conway Morris (1985). Vannier et al. 2006 assume that Tuzoia and the also Cambrian genus Isoxys are possibly representatives of the class Thylacocephala. Emmended diagnosis for the genus Isoxys by Garcia-Bellido 2009, p. 1224: ”Arthropod with one pair of cephalic appendages and a uniform series of at least 13 pairs of biramous appendages. Long, narrow body covered almost entirely by a bivalved, very thin unmineralized carapace. Prominent, stalked, spherical to pear-shaped lateral eyes protrude beyond the anterior margin of the carapace. Each valve armed with prominent cardinal spines. Dorsal outline straight or slightly projecting to form a weak to well-developed cusp (small circular node may be present below this cusp) anterior of mid-length. Ventral outline semicircular, weakly preplete (valve is highest anterior to its mid-length) to postplete (highest posterior to its mid-length). Simple perimarginal features (very narrow to more inflated rim). No flattened ⁄ concave marginal features. Narrow to broad doublure may be present. Carapace folded along the dorsal line (valves conjoined by a narrow band of cuticle; absence of articulating hinge). Internally, midgut glands may be present. External ornament may be expressed as uniform micro-reticulation or longitudinal striae. (Modified from Vannier and Chen 2000, p. 311)." Line drawing of Isoxys auritus from Fu et al 2014, p. 981: Identified by oilshale using Fu et al., 2014. References: Conway Morris, S. (1985). Cambrian Lagerstatten: their distribution and significance. Proceedings of the Royal Society B 311, 49–65. Fu, D., Zhang, X., Budd, G. E., Liu, W. & Pan, X. (2014). Ontogeny and dimorphism of Isoxys auritus (Arthropoda) from the Early Cambrian Chengjiang biota, South China. Gondwana Research, Volume 25, Issue 3, Pages 975-982. htttps://doi.org/10.1016/j.gr.2013.06.007. Fu, D.−J., Zhang, X.−L., and Shu, D.−G. (2011): Soft anatomy of the Early Cambrian arthropod Isoxys curvirostratus from the Chengjiang biota of South China with a discussion on the origination of great appendages. Acta Palaeontol. Pol. 56 (4): 843–852. Garcia-Bellido, D.C., Paterson, J.R., Edgecombe, G.D., Jago, J.B., Gehling, J.G. and Lee, M.S.Y. (2009). The bivalved arthropods Isoxys and Tuzoia with soft-part preservation from the Lower Cambrian Emu Bay Shale Lagerstätte (Kangaroo Island, Australia). Palaeontology, 52: 1221-1241. https://doi.org/10.1111/j.1475-4983.2009.00914.x Jiang, Z.W. (1982). Small shelly fossils. In: Luo, H.L., Jiang, Z.W., Wu, X.C., Song, X.L., Ou, Y.L. (Eds.), The Sinian-Cambrian Boundary in Eastern Yunnan, China. People's Publishing House of Yunnan, China, pp. 163–199. Shu, D.G., Zhang, X.-L. & Geyer, G. (1995). Anatomy and systematic affinities of the Lower Cambrian bivalved arthropod Isoxys auritus, Alcheringa: An Australasian Journal of Palaeontology, 19:4, 333-342, DOI: 10.1080/03115519508619512 Vannier, J., Chen, J.-Y., Huang, D.-Y. and Wang, X.-Q. (2006). Thylacocephalan arthropods: Their early Cambrian origin and evolutionary significance. Acta Paleontologica Polonica, 51:201–214.

Three species of Thylacocephala have been described from the Solnhofen Formation (“Solnhofen lithographic limestones”) so far: Clausocaris lithographica, Dollocaris michelorum, and Mayrocaris bucculata. A fourth new genus and species was newly described in 2019: Falcatacaris bastelbergeri. References: Braig, Florian, Haug, Joachim T., Schädel, Mario, and Haug, Carolin (2019): A new thylacocephalan crustacean from the Upper Jurassic lithographic limestones of southern Germany and the diversity of Thylacocephala. Palaeodiversity, 12(1) : 69-87

References: C. Haug, D. E. G. Briggs, D. G. Mikulic, J. Kluessendorf, and J. T. Haug (2014). The implications of a Silurian and other thylacocephalan crustaceans for the functional morphology and systematic affinities of the group. BMC Evolutionary Biology 14(159):1-15 [M. Clapham/M. Clapham] H. Polz (1989). Clausocaris nom. nov. pro Clausia Oppenheim 1888. Archaeopteryx 7:73 H. Polz (1993). Zur Metamerie von Clausocaris lithographica (Thylacocephala, ?Crustacea). Archaeopteryx. 11: 105-112. H. Polz (1992). Zur Lebensweise der Thylacocephala. Archaeopteryx. 10: 1-12.

References: Vannier, J., Chen, J.−Y., Huang, D.−Y., Charbonnier, S., and Wang, X.−Q. (2006). The Early Cambrian origin of thylacocephalan arthropods. Acta Palaeontologica Polonica 51 (2): 201–214. Vannier, J. et al. (2016) Exceptional preservation of eye structure in arthropod visual predators from the Middle Jurassic. Nat. Commun. 7:10320 doi: 10.1038/ncomms10320.