The Artiopodans, which comprise Trilobites plus a diverse range of Trilobite-like Arthropods, form an important part of all Palaeozoic marine communities, distinguished by a series of trunk appendages in similar morphology. Many biologists consider that the Artiopodans are still extant today, although they are divided as to whether the Chelicerates (Sea Spiders, Horseshoe Crabs, and Arachnids) or Mandibulates (Crustaceans, Insects, Millipedes and Centipedes) are living Artiopodans. Fossil Artiopodans are divided into two groups, the non-mineralised Trilobitomorphs and the mineralised Vicissicaudates.
The first Artiopodan fossil from the Chengjiang Biota of Yunnan Province was described in 1985, since when this Konservat-Lagerstätte has been recognised as having the highest known diversity of non-Trilobite Artiopodans of any known Cambrian deposit, and in particular the site from which most information about the appendages of these Arthropods has been gained.
In a paper published in the journal Acta Palaeontologica Polonica on 8 September 2023, Zhu Yuyan, Zeng Han, Lui Yao, and Zhao Fangchen of the State Key Laboratory of Palaeobiology and Stratigraphy at the Nanjing Institute of Geology and Palaeontology, describe three new species of Artiopodans from the Chengjiang Biota.
All three new species come from the Kuangshan section in Malong District, which is about 95 km to the northeast of Chengjiang, the type locality for the Chengjiang Biota. Here a yellowish mudstone considered to be part of the Maotianshan Shale Member of the Yu’anshan Formation has an intermixture of siltstone beds, and is interpreted to have been reworked since its original deposition.
The first new species described is named Zhugeia acuticaudata, where 'Zhugeia' refers to Zhuge Mountain where the Kuangshan section is located, which in turn is named after the ancient Chinese statesman Zhuge Liang, who reputedly once camped there, and 'acuticaudata' means 'spiney tail'. It is placed in the Trilobitomorph order Xandarellida, which is defined by having a semicircular cephalic shield (head-plate) with stalk lateral eyes that extend posteriorly to cover multiple thoracic tergites (plates covering back segments) and a pygidium (tail) with a broad median spine.
Zhugeia acuticaudata has a semi-elliptical cephalon with a pair of genal spines (spines emerging from the 'cheek'-section of the cephalon, and a pair of ovoid lateral eyes near anterior margin of the cephalon. The posterior of the cephalon covers the two forewardmost thoracic tergites. There are nine partially overlapping tergites with pleural spines (spines emerging from the outer edges of the tergites). The pygidium is small with two small lateral spines and an elongated needle-like median spine.
The second new species is named Tonglaiia bispinosa, where 'Tonglaiia' derives from 'Tonglai', an ancient name for Malong County, and 'bispinosa' means 'double-spined'. The phylogenetic affinities of this species are unclear.
Artiopodan Euarthropod Tonglaiia bispinosa from the Cambrian Stage 3 Chengjiang fauna at Malong, Yunnan, China; holotype NIGP 200050. (A) Whole specimen under high-angle light (A₁), under low-angle light (A₂), interpretative drawing (A₃). B. Left eye. (C) Left cephalic spine. (D) Right cephalic spine. (E) Right appendage. (F) Thoracic tergites (F₁) with spines (F₂). (G) Pygidium. Abbreviations: ap, appendage; ce, cephalon; cs, cephalic spine; e, eye; ml, marginal line around cephalon; pa, pleural angle; py, pygidium; sp, marginal spine; t1–t7, thoracic tergites; ts, terminal spine. Zhu et al. (2023).Tonglaiia bispinosa has an elliptical cephalon with a pair of marginal cephalic spines and two oval eyes situated near its anterior margin. There are seven partially overlapping tergites with posterolateral marginal spines. The pygidium is small with a pair of triangular spines at its posterior end.
The third new species described is placed in the Vicissicaudate genus Sidneyia, which was first described by Charles Doolittle Walcott in 1911, with a single species Sidneyia inexpectans, based upon specimens from the Burgess Shale, and given the specific name 'malongensis', meaning 'from Malong'. This is the second species of Sidneyia from Yunnan, with Sidneyia minor having been described from the Early Cambrian Xiaoshiba Biota. Specimens have also been assigned to Sidneyia cf inexpectans from the Mantou Formation of North China.
Sidneyia malongensis is described from two specimens. It has an oval-shaped exoskeleton composed of cephalon, thorax, and abdomen, with a body length of about 31 mm, and a maximum width is about 21 mm in the holotype and 15 mm in the paratype. The cephalon is semi-elliptical, measuring 6 mm long and 17 mm wide in holotype. The anterior margin of the cephalon is rounded, and posterior margin is straight. Lateral eyes are located at the genal angles of the cephalon. Eyes are also associated with notches on cephalon, although eye stalks are unclear. The presence of numerous wrinkles near the anterior margin indicates the convexity of the cephalon. The thorax consists of eight imbricated tergites of approximately equal length, measuring 16 mm long in the holotype and 12 mm long in the paratype. The overlapping area between adjacent thoracic tergites accounts for about one third of the sagittal length of each tergite. The posterior margin of the first three thoracic tergites is almost straight. The thorax is widest at the third or fourth thoracic tergite, measuring 8 mm wide in holotype, after which it gradually narrows and curves posteriorly. The pleural angle of each tergite is nearly equal along the thorax. No marginal spines are found on thoracic tergites. The abdomen consists of two overlapping cylindrical segments of subequal dimensions, measuring 4 mm long and 4 mm wide in holotype, as well as a tail fluke. The abdominal segments are narrower than the last thoracic tergite. The overlapping area between adjacent abdominal segments accounts for about one-fifth to one-fourth of sagittal length of each segment, with an average length of 1 mm. The tail fluke consists of a central triangular telson and a pair of flanked flaps, and is approximately as long as the abdominal segments.
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