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Although originally described as an alga, F. gyrata is now regarded by some authors as a coprolite (e.g., Steiner et al. 2005). Taxonomy from GBIF.org. Description and remarks by Chen and Zhou 1997., p. 88 : "Thread cylindrical, unbranchial, with a uniform, flattened width of 1.2mm and a preserved length of at least 20cm. Surface bears a tightly and helically coiled structure. Remarks: This is the most abundant alga in the Chengjiang biota. Most of the thread are preserved within a microturbidite mud layer and show irregular twisting, indicating that the thread was extremely flexible. Specimens probably sank to the bottom from the overlying water column, in a very low-energy environment, before the incursion of minor mud flow.” Restoration by Chen and Zhou 1997., p. 89: References: Chen, J.Y., and Zhou, G., (1997) Biology of the Chengjiang fauna. Bulletin of the National Museum of Natural Science, v. 10, p. 11–105. Hou, X., Aldridge, R., Bergstrom, J., Siveter, D.J., Siveter, D., and Feng, X., (2004) The Cambrian Fossils of Chengjiang, China: The Flowering of Early Animal Life. Malden, Wiley Blackwell, 233 p. Maletz, J., Steiner, M., and Fatka, O., (2005) Middle Cambrian pterobranchs and the question: What is a graptolite? Lethaia, v. 38, p. 73–85. Fu, X., Wu, M., Zhao, Y., Zhu, W., and Yang, Y., (2012) Discovery of macroalgae from the Cambrian Tsinghsutung Formation of Guizhou. Acta Palaeontologica Sinica, v. 51, p. 56–63. Wang, P.L., LoDuca, S. T., Wu, M. Y. et al., (2021) Benthic primary producers in exceptionally preserved Cambrian biotas of North China, Palaeoworld , https://doi.org/10.1016/j.palwor.2021.01.009

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 almostentirely 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)." Hou et al. 2007, p. 118: “This is one of three Isoxys species recorded from the Chengjiang biota. It is relatively rare and, unlike its Chengjiang associates Isoxys auritus and Isoxys curvirostratus, is known only from carapaces. The thin, elongate, bivalved carapace has a straight spine at both the anterodorsal and posterodorsal corners. The posterior spine is longer than the bivalved part of the carapace. Including both spines, carapace length can exceed 100mm. I. paradoxus can easily be distinguished from I. auritus by the unequal and total length of its spines. I. curvirostratus is distinguished from other species of the genus by having a curved anterior spine (Vannier & Chen 2000). Isoxys is a component of the earliest arthropod faunas worldwide. The genus is known from the Lower Cambrian of Spain, Siberia, South Australia and Southwest China and also from the Lower to Middle Cambrian of Laurentian North America. The ecology of Isoxys is discussed under I. auritus. I. paradoxus is unknown outside the Chengjiang biota.” Line drawing from Garcia-Bellido et al., p. 1224: Identified by oilshale using Hou et al, 2007. References: Hou Xian-guang (1987c) Early Cambrian large bivalved arthropods from Chengjiang, eastern Yunnan. Ada Palaeontologica Sinica, 26, 286-298. [In Chinese, with English summary]. Williams, M., Siveter, D.J. and Peel, J. (1996) Isoxys (Arthropoda) from the early Cambrian Sirius Passet Lagerstatte, North Greenland. Journal of Paleontology, 70, 947-954. Chen Jun-yuan & Zhou Gui-qing. (1997) Biology of the Chengjiang fauna. Bulletin of the National Museum of Natural Science, 10,11-106 Hou Xian-guang, Bergstrom, J., Wang Hai-feng, Feng Xiang-hong & Chen Ai-lin. (1999) The Chengjiang Fauna. Exceptionally well-preserved animals from 530 million years ago. 170 pp. Yunnan Science and Technology Press, Kunming, Yunnan Province, China. [In Chinese, with English summary] Vannier, J. and Chen, J.Y. (2000) The Early Cambrian colonization of pelagic niches exemplified by Isoxys (arthropoda). Lethaia 33, 295–311. 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. Hou Xian-guang, Aldridge, R., Bergstrom, J., Siveter David J., Siveter Derek J. and Feng Xiang-Hong (2007) The Cambrian Fossils of Chengjiang, China: The Flowering of Early Animal Life, Wiley-Blackwell, ISBN 10: 1405106735. 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

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.