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| Dianhaia heptacantha Zhu, Zeng, Liu & Zhao, 2026 |
Abstract
Helmetiida is a major group of Trilobitomorpha and Artiopoda known from Cambrian Burgess Shale-type Lagerstätten. Phylogenetic studies have suggested that they are closely related to trilobites as their possible sister taxon. With seven genera and eight species, Helmetiida has only been found in the Burgess Shale and the Chengjiang biota. Here we describe a new helmetiid, Dianhaia heptacantha n. gen. n. sp., from the early Cambrian Chengjiang biota (Cambrian Series 2, Stage 3), Yunnan Province, South China. Dianhaia heptacantha n. gen. n. sp. possesses an anterior sclerite that is diagnostic of Helmetiida. The semicircular cephalon bears a pair of short genal spines. The thorax consists of seven tergites, each having a pair of long pleural spines and showing edge-to-edge articulation. The pygidium carries one short terminal spine and three pairs of long lateral spines. Dianhaia heptacantha n. gen. n. sp. is distinguished from other helmetiids by different numbers of thoracic tergites and pygidial spines. Computed microtomography shows that D. heptacantha n. gen. n. sp. has a pair of antennae and 13 pairs of homonomous biramous appendages. Each biramous appendage consists of a gnathobasic protopodite, seven-podomerous endopodite, and a lobate exopodite with lamellae. Phylogenetic analysis of Artiopoda resolved Dianhaia n. gen. as the sister taxon of Haifengella within Helmetiida. The discovery of this new helmetiid enriches the taxonomic diversity and appendicular morphoanatomy of Cambrian trilobitomorphs from the Chengjiang biota.
Systematic paleontology
Euarthropoda Lankester, 1904
Artiopoda Hou and Bergström, 1997
Trilobitomorpha Størmer, 1944
Conciliterga Hou and Bergström, 1997
Helmetiida Novozhilov, 1960
Helmetiidae Simonetta and Delle Cave, 1975
Included genera: Helmetia Walcott, 1918; Kuamaia Hou, 1987; Rhombicalvaria Hou, 1987; Haifengella Zhao et al., 2014.
Genus Dianhaia new genus
Etymology: Derived from Dianhai, another name of the Dian Lake, which is close to the fossil locality.
Remarks: Dianhaia n. gen. has an oval anterior sclerite and tergites with edge-to-edge articulation, supporting its assignment to Helmetiida. Its well-developed segmental boundaries and several large pygidial spines indicate that it was a member of Helmetiidae (Losso et al., 2025). Different from Helmetia and Kuamaia, Dianhaia n. gen. has long pleural spines and pygidial spines that are similar to the counterparts in Rhombicalvaria and Haifengella (Hou and Bergström, 1997; Zhao et al., 2014; Losso et al., 2025). But compared with Rhombicalvaria and Haifengella, Dianhaia n. gen. has different numbers of thoracic tergites and pygidial spines, suggesting it is a separate genus.
Dianhaia heptacantha new species
Holotype: NIGP 203984a, b, part and counterpart.
Materials: Holotype (NIGP 203984a, b); paratype (NIGP 203985).
Diagnosis: The cephalic shield possesses a pair of short genal spines. The thorax comprises seven thoracic tergites with long pleural spines. The semicircular pygidium bears one very short terminal spine and three pairs of long lateral spines. Biramous appendages have an undivided long-ovate flap with marginal setae and imbricated lamellae.
Occurrence: Maotianshan Shale Member, Yu’anshan Formation, Wutingaspis–Eoredlichia trilobite Zone, Cambrian Series 2, Stage 3, Jianshan section, Kunming City, Yunnan Province, China.
Etymology: Hepta means seven in Greek. Acantha means spine in Greek. The name derives from the seven pairs of thoracic spines and seven pygidial spines in this species.
Yuyan Zhu, Han Zeng, Yao Liu and Fangchen Zhao. 2026. A non-biomineralized trilobitomorph euarthropod (Helmetiida) with appendicular morphology from the early Cambrian Chengjiang Biota, China. Journal of Paleontology. First View, pp. 1 - 10. DOI: doi.org/10.1017/jpa.2026.10257 [07 October 2026]













































