Hostname: page-component-74656f9884-npj9w Total loading time: 0 Render date: 2026-11-07T01:54:26.050Z Has data issue: false hasContentIssue false
  • English
  • Français

A non-biomineralized trilobitomorph euarthropod (Helmetiida) with appendicular morphology from the early Cambrian Chengjiang biota, China

Published online by Cambridge University Press:  07 October 2026

Yuyan Zhu ,
Han Zeng Open the ORCID record for Han Zeng [Opens in a new window] ,
Yao Liu  and
Fangchen Zhao Open the ORCID record for Fangchen Zhao [Opens in a new window]
Yuyan Zhu
Affiliation:
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences , Nanjing 210008, China University of Chinese Academy of Sciences , Beijing 100049, China
Han Zeng*
Affiliation:
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences , Nanjing 210008, China University of Chinese Academy of Sciences , Beijing 100049, China
Yao Liu
Affiliation:
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences , Nanjing 210008, China University of Chinese Academy of Sciences , Beijing 100049, China
Fangchen Zhao
Affiliation:
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences , Nanjing 210008, China University of Chinese Academy of Sciences , Beijing 100049, China
*
Corresponding author: Han Zeng; Email: hzeng@nigpas.ac.cn
Rights & Permissions [Opens in a new window]

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.

UUID: http://zoobank.org/1e9c8dcc-b4e2-4c3e-a2e3-9945692e0c68

Information

Type
Articles
Information
Journal of Paleontology , First View , pp. 1 - 10
Check for updates
Creative Commons
Creative Common License - CCCreative Common License - BYCreative Common License - NCCreative Common License - ND
This is an Open Access article, distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives licence (http://creativecommons.org/licenses/by-nc-nd/4.0), which permits non-commercial re-use, distribution, and reproduction in any medium, provided that no alterations are made and the original article is properly cited. The written permission of Cambridge University Press or the rights holder(s) must be obtained prior to any commercial use and/or adaptation of the article.
Copyright
© The Author(s), 2026. Published by Cambridge University Press on behalf of Paleontological Society

Non-technical Summary

Trilobitomorph arthropods comprise the biomineralized trilobites and their non-biomineralized relatives. Compared to the highly diverse trilobites, the soft-bodied trilobitomorphs are much rarer in the fossil record, because they are only known from exceptionally preserved fossil deposits. Here we describe a new genus and species of trilobitomorph, Dianhaia heptacantha, from the 518-million-year-old early Cambrian Chengjiang biota in Yunnan Province, South China. Based on the appendages exposed on the surface of fossils and the morphologies of appendages revealed by X-ray computed tomography, we reconstructed the complete set of appendages of Dianhaia. This discovery expands the biodiversity of Cambrian trilobitomorphs and enriches our knowledge about their soft-bodied anatomy.

Introduction

Artiopoda Hou and Bergström, Reference Hou and Bergström1997, comprises trilobites and their relatives, representing a major euarthropod group during the Paleozoic (Whittington et al., Reference Whittington, Chatterton, Speyer, Fortey, Owens, Chang, Dean, Jell, Laurie and Palmer1997; Edgecombe and Ramsköld, Reference Edgecombe and Ramsköld1999; Ortega-Hernández et al., Reference Ortega-Hernández, Legg and Braddy2013). During the early Cambrian, non-trilobite artiopodans, mostly non-biomineralized trilobitomorphs, emerged and proliferated almost contemporaneously with the rapid diversification of trilobites (Hughes, Reference Hughes2007; Holmes and Budd, Reference Holmes and Budd2022). Trilobitomorpha Størmer, Reference Størmer1944, which is characterized by the presence of undifferentiated biramous post-antennal appendages in cephalon, thorax, and pygidium, contains several groups such as Trilobita Walch, Reference Walch1771, Petalopleura Hou and Bergström, Reference Hou and Bergström1997, Nektaspida Raymond, Reference Raymond1920, and Conciliterga Hou and Bergström, Reference Hou and Bergström1997 (Ortega-Hernández et al., Reference Ortega-Hernández, Legg and Braddy2013). Unlike trilobites, trilobitomorphs lack a biomineralized exoskeleton, and are found predominantly in Cambrian Konservat-Lagerstätten (Briggs et al., Reference Briggs, Erwin, Collier and Clark1994; Hou and Bergström, Reference Hou and Bergström1997; Stein et al., Reference Stein, Budd, Peel and Harper2013; Hou et al., Reference Hou, Siveter, Siveter, Aldridge, Cong, Gabbott, Ma, Purnell and Williams2017; Fu et al., Reference Fu, Tong, Dai, Liu, Yang, Zhang, Cui, Li, Yun and Wu2019; Edgecombe et al., Reference Edgecombe, García-Bellido and Paterson2025; Zhu et al., Reference Zhu, Zhao, Zeng, Huang, Li, G.X. and Luo2025).

As a major group of Trilobitomorpha, Conciliterga comprises Arthroaspis and Helmetiida, the latter including Tegopeltidae Simonetta and Delle Cave, Reference Simonetta and Delle Cave1975, and Helmetiidae Simonetta and Delle Cave, Reference Simonetta and Delle Cave1975 (Losso et al., Reference Losso, Caron and Ortega-Hernández2025). Helmetiids share an anterior sclerite and edge-to-edge articulated tergites. In some phylogenetic studies, helmetiids have been retrieved as close relatives of trilobites or as the sister group of Trilobita (Edgecombe and Ramsköld, Reference Edgecombe and Ramsköld1999; Ortega-Hernández et al., Reference Ortega-Hernández, Legg and Braddy2013; Chen et al., Reference Chen, Ortega-Hernández, Wolfe, Zhai, Hou, Chen, Mai and Liu2019; Berks et al., Reference Berks, Lunde Nielsen, Flannery-Sutherland, Thorshøj Nielsen, Park and Vinther2023; Zhu et al., Reference Zhu, Zeng, Liu and Zhao2023). Tegopeltidae, which features fused thoracic tergites and lack of pleural or pygidial spines, includes Tegopelte Simonetta and Delle Cave, Reference Simonetta and Delle Cave1975, from the Burgess Shale, as well as Saperion Hou et al., Reference Hou, Ramsköld and Bergström1991, and Skioldia Hou and Bergström, Reference Hou and Bergström1997, from the Chengjiang biota. Helmetiidae are characterized by the non-effaced boundaries between thoracic tergites and well-developed pleural and pygidial spines, including Helmetia Walcott, Reference Walcott1918, from the Burgess Shale, along with Rhombicalvaria Hou, Reference Hou1987, Kuamaia Hou, Reference Hou1987, and Haifengella Zhao et al., Reference Zhao, Hu, Zeng and Zhu2014, from the Chengjiang biota.

Among the currently known Helmetiida, five of the seven genera and six of the eight species have been described from the Chengjiang biota (Hou, Reference Hou1987; Hou and Bergström, Reference Hou and Bergström1997; Zhao et al., Reference Zhao, Hu, Zeng and Zhu2014). Although preservation of appendages has been reported from nearly all helmetiid genera, only Kuamaia and Saperion have been reconstructed with complete morphologies of post-antennular appendages (Shu and Zhang, Reference Shu and Zhang1996; Hou and Bergström, Reference Hou and Bergström1997; Edgecombe and Ramsköld, Reference Edgecombe and Ramsköld1999; O’Flynn et al., Reference O’Flynn, Williams, Liu, Hou, Guo and Edgecombe2025). Here we describe a new helmetiid with ventral anatomy and detailed appendicular morphology from the Chengjiang biota, with its phylogenetic placement analyzed and discussed. These discoveries provide new insights into the taxonomic and morphological diversity of Cambrian trilobitomorphs and artiopodans.

Materials and methods

The fossil material (NIGP 203984, 203985) was collected from the fossiliferous interval of the Chengjiang biota, the yellowish shale of the Maotianshan Shale Member, Yu’anshan Formation, at the Jianshan section in the Haikou area, Kunming City, Yunnan Province, China. At the Jianshan section, the Yu’anshan Formation is incomplete and is 49.3 m thick in total (Han et al., Reference Han, Shu, Zhang, Liu, Zhang and Yao2006). In the Haikou–Jinning area, the upper part of the Yu’anshan Formation has a disconformable contact with the Middle Devonian Haikou Formation (Zhao et al., Reference Zhao, Hu, Caron, Zhu, Yin and Lu2012; Zhu et al., Reference Zhu, Zhao, Zeng, Huang, Li, G.X. and Luo2025). The Maotianshan Shale Member in the Haikou area consists of thin, single-event and background mudstone layers (Zhao et al., Reference Zhao, Hu, Caron, Zhu, Yin and Lu2012). The trilobites co-occurring with the non-trilobite artiopodans include Eoredlichia intermedia (Lu, Reference Lu1940), and Yunnanocephalus yunnanensis (Mansuy, Reference Mansuy1912). This trilobite fossil assemblage indicates that these fossils belong to the upper part of Wutingaspis–Eoredlichia trilobite interval zone (Steiner et al., Reference Steiner, Zhu, Weber and Geyer2001).

The specimens were photographed by using a Zeiss Axio Zoom V16 stereomicroscope and a Nikon D810 camera with a Micro-Nikkor 105 mm f/2.8 lens. Tomography data were acquired with a ZEISS Xradia 520 Versa X-ray microscope. Tomographic scanning was performed with a 0.4× objective, LE3 or LE4 filter, and under conditions of 60 kV and 5 W or 80 kV and 10 W. For each specimen, 1401 or 2001 tomographic projections were collected with an exposure time of 1 second per projection. The data were segmented and rendered using VG Studio Max 2023.1. Morphological terminology used in this paper mainly follows Ortega-Hernández et al. (Reference Ortega-Hernández, Legg and Braddy2013), Zhao et al. (Reference Zhao, Hu, Zeng and Zhu2014), and Losso et al. (Reference Losso, Caron and Ortega-Hernández2025).

The phylogenetic dataset is composed of 72 taxa and 98 characters, with the new helmetiid taxon added to the dataset of Losso et al. (Reference Losso, Caron and Ortega-Hernández2025). Character states of Tremaglaspis were revised according to Fortey and Rushton (Reference Fortey and Rushton2009) and Lerosey-Aubril et al. (Reference Lerosey-Aubril, Ortega-Hernández, Kier and Bonino2013) (see supplementary material for details). The data matrix was analyzed with parsimony and Bayesian methods. The maximum parsimony analyses were conducted in TNT v.1.5 (Goloboff and Catalano, Reference Goloboff and Catalano2016). All characters were treated as unordered. Each analysis, with equal or implied weighting setting of characters applied (concavity values k = 1–10, 20, ∞) (Goloboff, Reference Goloboff1993), consisted of a traditional search comprising 1,000 replicates of tree bisection and reconnection (TBR) with 1,000 trees saved per replicate. Bootstrap, jackknife, and group present/contradicted (GC) values were calculated for nodal supports (Goloboff et al., Reference Goloboff, Farris, Källersjö, Oxelman, Ramıacuterez and Szumik2003). The Bayesian phylogenetic analysis was performed in MrBayes v.3.2.7a (Ronquist et al., Reference Ronquist, Teslenko, van der Mark, Ayres, Darling, Höhna, Larget, Liu, Suchard and Huelsenbeck2012). Two parallel runs with four Markov chains per run were performed under the default Markov chain Monte Carlo (MCMC) settings and default priors. Trees were sampled every 1,000 generations with the first 25% samples discarded as burn-in. The Mkv model for discrete morphological data and a gamma distribution for rate heterogeneity between characters were applied (Lewis, Reference Lewis2001). A 50% majority-rule consensus tree was generated to summarize the Bayesian inference results. The convergence of MCMC runs was verified by the fuzzy caterpillar-shaped traces, effective sample sizes > 5,500, and average standard deviation of split frequencies < 0.003 in Tracer 1.7.2 (Rambaut et al., Reference Rambaut, Drummond, Xie, Baele and Suchard2018).

Repository and institutional abbreviation

All the specimens are deposited in the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (NIGP).

Systematic paleontology

Euarthropoda Lankester, Reference Lankester1904

Artiopoda Hou and Bergström, Reference Hou and Bergström1997

Trilobitomorpha Størmer, Reference Størmer1944

Conciliterga Hou and Bergström, Reference Hou and Bergström1997

Helmetiida Novozhilov, Reference Novozhilov1960

Helmetiidae Simonetta and Delle Cave, Reference Simonetta and Delle Cave1975

Included genera

Helmetia Walcott, Reference Walcott1918; Kuamaia Hou, Reference Hou1987; Rhombicalvaria Hou, Reference Hou1987; Haifengella Zhao et al., Reference Zhao, Hu, Zeng and Zhu2014.

Genus Dianhaia new genus

Type and only species

Dianhaia heptacantha n. sp.

Diagnosis

As for the type species.

Occurrence

As for the type species.

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., Reference Losso, Caron and Ortega-Hernández2025). 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, Reference Hou and Bergström1997; Zhao et al., Reference Zhao, Hu, Zeng and Zhu2014; Losso et al., Reference Losso, Caron and Ortega-Hernández2025). 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

Figures 1–3

Figure 1.

Dianhaia heptacantha n. gen. n. sp. from the Cambrian Stage 3 Chengjiang biota, holotype NIGP 203984, part and counterpart. (1, 2, 4–9) Part, NIGP 203984a; (1) whole specimen; (2) interpretative drawing; (4) endopodite; (5) a thoracic biramous appendage; (6) exopodite; (7) setae on the exopodite; (8) spines on the pleural spine; (9) spines on the pygidium. (3) Counterpart, NIGP 203984b. Scale bars represent 5 mm (1, 2), 1 mm (3, 7), 2 mm (4–6, 8, 9). Abbreviations: as, anterior sclerite; ce, cephalic segment; cs, cephalic shield; cw, claw; ed, endite; en, endopodite; ex, exopodite; gs, genal spine; gn, gnathobase; hy, hypostome; lm, lamella; ls, lateral spine; ps, pleural spine; pt, protopodite; py, pygidium; sp, marginal spine; ts, terminal spine; T1–7, thoracic tergite 1–7; xs, setae on exopodite.

A nine-panel composite showing the holotype fossil and anatomical details of Dianhaia heptacantha. See long description.
Figure 1. Long description

A collection of nine panels including photographs and a line drawing of the holotype N I G P 203984.

* Panel 1: A photograph of the whole specimen part showing a segmented body with lateral spines and appendages preserved in reddish-brown on a tan matrix.

* Panel 2: An interpretative line drawing of Panel 1. From top to bottom, it labels the anterior sclerite a s, hypostome h y, cephalic shield c s, and cephalic segments c e 2 through c e 4. The thorax consists of seven tergites T 1 through T 7, each with a pleural spine p s. The posterior ends in a pygidium p y with lateral spines l s 1 through l s 3 and a terminal spine t s. Appendages include the exopodite e x and endopodite e n.

* Panel 3: A photograph of the counterpart specimen N I G P 203984 b, showing the anterior region with labels for a s, h y, e n 2 through e n 4, c e 2 through c e 4, and T 1 through T 3.

* Panel 4: Close-up of an endopodite showing the protopodite p t and five podomeres numbered 1 to 5, with endites e d protruding from the inner margin.

* Panel 5: A thoracic biramous appendage showing the p t, gnathobase g n, and a six-segmented endopodite with a terminal claw c w. The exopodite e x is visible as a broad lobe.

* Panel 6: Detail of an endopodite and exopodite e x showing fine lamellae l m.

* Panel 7: High magnification of setae x s on the exopodite e x.

* Panel 8: Detail of the pleural spine p s showing small marginal spines s p along the edge.

* Panel 9: Detail of the pygidium showing marginal spines s p and the terminal spine t s.

Scale bars are provided for each panel: 5 mm for panels 1 and 2; 1 mm for panels 3 and 7; 2 mm for panels 4, 5, 6, 8, and 9.

Figure 2.

Dianhaia heptacantha n. gen. n. sp. from the Cambrian Stage 3 Chengjiang biota, paratype NIGP 203985. (1) Whole specimen; (2) interpretative drawing; (3) pygidial segments; (4) cephalic and anterior thoracic segments with appendages; (5) marginal spines on the pygidial pleural spine; (6) marginal spines on the pygidium; (7) whole appendage; (8) endopodite; (9) setae on exopodite. Scale bars represent: 5 mm (1, 2), 2 mm (3), 1 mm (4–9). Abbreviations: as, anterior sclerite; en, endopodite; ex, exopodite; ls, lateral spine; ps, pleural spine; pt, protopodite; py, pygidium; sp, marginal spine; st, sternite; ts, terminal spine; T1–7, thoracic tergite 1–7; xs, setae on exopodite.

A nine-panel figure showing fossil photographs and interpretive drawings of the Cambrian arthropod Dianhaia heptacantha. See long description.
Figure 2. Long description

Panel 1 is a photograph of the whole specimen paratype N I G P 203985, showing a flattened reddish-brown fossil on a tan matrix with rectangular boxes highlighting anatomical details. Panel 2 is a line drawing interpreting the specimen, showing an anterior sclerite (a s) at the top, followed by sternites (s t) along the midline, thoracic tergites labeled T 1 through T 7, and a posterior pygidium (p y) with lateral spines (l s) and a terminal spine (t s). Panel 3 provides a close-up of the posterior thoracic segments T 6 and T 7. Panel 4 shows the cephalic and anterior thoracic region, labeling the anterior sclerite (a s), endopodites (e n), exopodites (e x), protopodites (p t), and sternites (s t). Panel 5 details marginal spines (s p) on a pleural spine (p s). Panel 6 shows marginal spines (s p) on the pygidium (p y) near a lateral spine (l s). Panel 7 displays a whole appendage with protopodite, endopodite, and exopodite. Panel 8 focuses on an endopodite with segments numbered 1 through 6. Panel 9 shows fine setae (x s) on an exopodite (e x). Scale bars indicate 5 millimeters for panels 1 and 2, 2 millimeters for panel 3, and 1 millimeter for panels 4 through 9.

Figure 3.

Tomographic images of Dianhaia heptacantha n. gen. n. sp., holotype NIGP 203984. (1–6, 8) Maximum projection images; (7, 9) volume rendering images; (1–7) dorsal view; (8, 9) ventral view. (1) Whole specimen; (2) virtual section showing appendages from cephalon and anterior thorax; (3) setae on exopodite; (4) exopodite lamellae, under image stacking; (5) antenna; (6, 7) appendages from posterior thorax and pygidium; (8, 9) endopodite. Scale bars represent: 3 mm (1), 2 mm (2), 1 mm (3–9). Abbreviations: an, antenna; cw, claw; ed, endite; en, endopodite; ex, exopodite; gn, gnathobase; lm, lamella; pt, protopodite; sp, marginal spine; xs, setae on exopodite.

Nine tomographic and volume rendering panels showing the holotype of Dianhaia heptacantha n. gen. n. sp. including dorsal and ventral views of appendages and setae. See long description.
Figure 3. Long description

A nine-panel collection of tomographic images.

Panel 1: A whole specimen in dorsal view with boxes indicating regions for subsequent panels. Labels include a n for antenna, e n for endopodite, and e x for exopodite.

Panel 2: Virtual section of the cephalon and anterior thorax. Labels show e n for endopodite, p t for protopodite, e x for exopodite, x s for setae, and l m for lamella.

Panel 3: Close-up of a curved e x exopodite covered in fine x s setae.

Panel 4: High-magnification image stacking showing parallel l m lamellae.

Panel 5: Detail of the a n antenna showing a row of s p marginal spines on one side and small arrowheads on the opposite side.

Panel 6: Appendages from the posterior thorax and pygidium. Labels identify e d for endite, g n for gnathobase, p t for protopodite, l m for lamella, e x for exopodite, c w for claw, and x s for setae. Numbers 1 through 6 mark segments along the limb.

Panel 7: A 3 D volume rendering of the appendages shown in panel 6, highlighting the spatial structure of the endopodites and exopodites.

Panel 8: Ventral view of an e n endopodite. Labels show g n gnathobase at the proximal end, p t protopodite, e d endites on segments 1 through 4, and a distal c w claw on segment 6. An e x exopodite with x s setae is attached laterally.

Panel 9: A 3 D volume rendering of the ventral endopodite from panel 8, showing the thickness and orientation of the spines and segments.

Scale bars are provided for each panel: 3 millimeters for panel 1; 2 millimeters for panel 2; and 1 millimeter for panels 3 through 9.

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.

Description

The oval exoskeleton consists of cephalon, thorax, and pygidium (Figs. 1.1, 2.1). The sagittal body length from the anterior margin of anterior sclerite to the posterior extremity of pygidium, including the length of terminal pygidial spine, is about 23 mm in the holotype and around 32 mm in the paratype. Ratio of the three body parts is approximately 6:10:7, as calculated from the holotype. Maximum body width, with pleural spines excluded, is seen in the second thoracic tergite, which measures about 12 mm in the paratype.

The cephalon is semi-elliptical with a pair of short genal spines (‘gs’ in Fig. 1.1, 1.2). The length:width ratio is around 3:7. The cephalic lateral margins are smooth and rounded, without marginal spines. An oval anterior sclerite is associated with the anterior margin of cephalic shield (‘as’ in Figs. 1.1–1.3, 2.1, 2.2, 2.4). The sagittal length of anterior sclerite is about one-fifth of the sagittal length of cephalic shield.

The thorax consists of seven morphologically similar ribbon-shaped thoracic tergites. Thoracic tergites have edge-to-edge articulations between them in general. Overlaps between adjacent tergites can be seen in the axial region. The first two tergites arch slightly anteriorly, while the last three tergites reflex anteriorly. Each side of a thoracic tergite develops into a long pleural spine (‘ps’ in Figs. 1.8, 2.5). The pleural spine of first thoracic tergite is longer than the genal spine of cephalic shield. The pleural spines increase in length from the first to third thoracic tergite, while being of almost equal length posteriorly. Tiny spines are evenly distributed along the anterior margin of pleural spines (‘sp’ in Figs. 1.8, 2.5).

The broad and large pygidium has a semicircular shape. The pygidium is isopygous and is only slightly longer than cephalon. The margin of pygidium bears three pairs of lateral spines and one terminal spine (‘ls’, ‘ts’ in Figs. 1.1, 1.2, 2.1, 2.2). The elongated and pointed lateral spines are much longer than the very short terminal spine. The lateral pygidial spines are similar in length to the posterior thoracic pleural spines. The terminal spine has a broader base than the lateral spines. Margins of both the terminal and lateral spines are accompanied by numerous tiny marginal spines (‘sp’ in Figs. 1.9, 2.6). The density of spines on the terminal spine is greater than that on lateral spines.

In the ventral view of cephalon, an oval hypostome is situated behind anterior sclerite (‘hy’ in Fig. 1.3). A pair of antennae are attached to the sides of hypostome (‘an’ in Fig. 3.1). The antennae are robust and composed of at least eight subrectangular podomeres (Fig. 3.5). Each podomere has two long, needle-shaped spines on the inner side, which are close to the distal arthrodial membrane (‘sp’ in Fig. 3.5).

Following the antennae are 13 pairs of homonomous biramous appendages. Three pairs are on the cephalon (Fig. 1.3), seven pairs on the thorax, and three pairs on the pygidium (Figs. 3.6, 3.7, 4). The size of post-antennal appendages gradually increases in the anterior body part, reaching the maximum dimension on the second thoracic segment, and gradually diminishes towards rear. Each appendage consists of a protopodite, an endopodite, and an exopodite (Figs. 1.5, 2.7, 3.6, 3.7).

Figure 4.

Reconstruction of the helmetiid euarthropod Dianhaia heptacantha n. gen. n. sp. from the Cambrian Stage 3 Chengjiang biota. (1) Dorsal view; (2) ventral view. The reconstruction is based on the following figures: Tergites (Fig. 1.1); sternites (Fig. 2.1, 2.3); anterior sclerite (Figs. 1.3, 2.4); hypostome (Fig. 1.3); antennae (Fig. 3.5); protopodite (Fig. 3.6, 3.8); endopodite (Figs. 1.4, 3.6, 3.8); exopodite (Figs. 2.7, 3.3, 3.6); lamellae (Fig. 3.4). Morphology of the articular membrane and position of antennae are inferred. The number of antennal podomeres was referred from Kuamaia lata.

Two-panel anatomical reconstruction of the Cambrian euarthropod Dianhaia heptacantha showing dorsal and ventral views with color-coded morphological features. See long description.
Figure 4. Long description

A two-panel scientific illustration of a helmetiid euarthropod.

Panel 1, Dorsal View:

Shows the upper surface of the organism. At the anterior end, two long, segmented antennae extend outward, featuring fine bristles on their inner margins. The body is covered by a series of overlapping tergites. The most anterior tergite is a large, rounded head shield. This is followed by eleven thoracic tergites that taper slightly toward the rear. The posterior end terminates in a large tail shield with seven distinct marginal spines.

Panel 2, Ventral View:

Shows the underside of the organism. Along the central axis is a series of rectangular sternites. At the very front, an anterior sclerite and a small, central hypostome are visible between the bases of the antennae. Branching out from the central axis are pairs of biramous appendages. Each appendage consists of a thick proximal protopodite, a multi-segmented endopodite used for walking, and a broad, fan-like exopodite. The exopodites are lined with fine, parallel lamellae.

A color-coded legend at the bottom identifies the following structures:

* Tergite: light beige

* Sternite: medium gray

* Anterior sclerite: pale yellow-green

* Hypostome: brownish-pink

* Antenna: light tan

* Protopodite: olive brown

* Endopodite: cream

* Exopodite: grayish-brown

* Lamellae: dark charcoal gray

The protopodite consists of a single subrectangular podomere, with a robust gnathobase bearing numerous spines (‘pt, gn’ in Figs. 1.4, 1.5, 2.7, 2.8, 3.6–3.9). The gnathobasic spines point proximally. Each protopodite attaches to its corresponding sternite (‘st’ in Fig. 2.1, 2.2). The endopodite and exopodite are connected to the distal end of protopodite.

Each endopodite is composed of seven podomeres (Figs. 1.4, 1.5, 2.8, 3.6–3.9). The proximal six podomeres are approximately rectangular in outline, and their sizes decrease gradually distally (Fig. 3.6–3.9). The lengths of podomeres increase and the diameters decrease towards rear. Endite is present at each podomere and is adorned with a cluster of elongated spines (‘ed’ in Fig. 3.6–3.9). From the first to seventh podomere, the position of endite shifts progressively from a proximal to a distal position. The endites of appendages are notable for their lengths, with each endite featuring a relatively long, needle-shaped spine (‘ed’ in Fig. 3.8, 3.9). At the terminal of the endopodite, the seventh podomere is a short, sharp claw (‘cw’ in Figs. 1.5, 3.6–3.9).

The exopodite consists of an undivided flattened lobate flap with a long-ovate outline (‘ex’ in Figs. 1.5–1.7, 2.7, 3.2). Numerous setae, a few hundred micrometers long, are evenly distributed along the distal margin of the exopodite (‘xs’ in Fig. 2.9, 3.3). A row of imbricated lamellae is attached to the dorsal margin of the proximal exopodite (‘lm’ in Fig. 3.2, 3.4). The exopodite, including its setae, is longer than the endopodite.

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.

Remarks

Helmetiidae exhibits marked variations in body size (Table 1). Among all Helmetiidae, Dianhaia n. gen. has a relatively small body size that is comparable to Haifengella (Zhao et al., Reference Zhao, Hu, Zeng and Zhu2014). Helmetia is considerably larger than the members of Helmetiidae from the Chengjiang biota (Losso et al., Reference Losso, Caron and Ortega-Hernández2025), while Kuamaia muricata Hou and Bergström, Reference Hou and Bergström1997, has the smallest body size (Hou and Bergström, Reference Hou and Bergström1997).

Table 1.

Morphological comparisons of Helmetiidae

A morphological comparison table of Helmetiidae species including body dimensions, thoracic tergites, and pygidial spines. See long description.
Table 1. Long description

The table contains seven columns: Species, Body length in m m, Body width in m m, Thoracic tergites, Pygidial spines, Specimen, and Reference.

* Helmetia expansa: 196 m m length, 125 m m width, 6 thoracic tergites, 5 pygidial spines, specimen U S N M 83952, reference Briggs et al., 1994.

* Kuamaia lata: 59 m m length, 38.7 m m width, 7 thoracic tergites, 5 pygidial spines, specimen C N 115318, reference Hou and Bergström, 1997.

* Kuamaia muricata: 14.8 m m length, 8.7 m m width, 8 thoracic tergites, 7 pygidial spines, specimen C N 115401, reference Hou and Bergström, 1997.

* Rhombicalvaria acantha: 80 m m length, 40 m m width, 9 thoracic tergites, 5 pygidial spines, specimen N I G P 100136, reference Hou, 1987.

* Haifengella corona: 28 m m length, 17 m m width, 6 thoracic tergites, 5 pygidial spines, specimen N I G P 158639, reference Zhao et al., 2014.

* Dianhaia heptacantha n. gen. n. sp.: 23 m m length, 12 m m width, 7 thoracic tergites, 7 pygidial spines, specimen N I G P 203984 a, reference This study.

Dianhaia n. gen. has a similar body architecture with other Helmetiidae, including a semi-elliptical cephalon, edge-to-edge tergal articulations, and a semicircular pygidium with several tail spines (Hou and Bergström, Reference Hou and Bergström1997; Losso et al., Reference Losso, Caron and Ortega-Hernández2025). However, Dianhaia also shows prominent differences from other species.

Dianhaia n. gen. has a cephalon with a pair of short genal spines, which is similar to Kuamaia lata Hou, Reference Hou1987, and K. muricata (Hou and Bergström, Reference Hou and Bergström1997). By contrast, the genal spines in Haifengella and Rhombicalvaria are elongate (Hou, Reference Hou1987; Zhao et al., Reference Zhao, Hu, Zeng and Zhu2014). Distinct from all the above, the cephalon of Helmetia has a unique concave anterior margin with a pair of prominent anterolateral spines (Briggs et al., Reference Briggs, Erwin, Collier and Clark1994; Losso et al., Reference Losso, Caron and Ortega-Hernández2025).

Both Dianhaia n. gen. and Kuamaia lata have seven thoracic tergites (Hou, Reference Hou1987), while the number is six in Helmetia and Haifengella (Briggs et al., Reference Briggs, Erwin, Collier and Clark1994; Zhao et al., Reference Zhao, Hu, Zeng and Zhu2014), eight in K. muricata (Hou and Bergström, Reference Hou and Bergström1997), and nine in Rhombicalvaria (Hou, Reference Hou1987). However, with long pleural spines, the thoracic morphology of Dianhaia n. gen. differs from that of K. lata and is instead more similar to that of Haifengella (Hou, Reference Hou1987; Hou and Bergström, Reference Hou and Bergström1997; Zhao et al., Reference Zhao, Hu, Zeng and Zhu2014). Elongate pleural spines are also present in Haifengella and Rhombicalvaria, but they are more acute (Hou, Reference Hou1987; Zhao et al., Reference Zhao, Hu, Zeng and Zhu2014). The pleural spines in K. lata, K. muricata, and Helmetia are shorter and blunter (Hou and Bergström, Reference Hou and Bergström1997; Briggs et al., Reference Briggs, Erwin, Collier and Clark1994; Losso et al., Reference Losso, Caron and Ortega-Hernández2025).

The pygidial spines of Helmetiidae show notable variations in morphology and number. Dianhaia n. gen. bears three pairs of lateral spines and one terminal spine. Although Dianhaia has the same number of spines as K. muricata, spines of the former are longer and sharper (Hou and Bergström, Reference Hou and Bergström1997). These longer and sharper lateral spines are more similar to those of Haifengella and Rhombicalvaria (Hou, Reference Hou1987; Zhao et al., Reference Zhao, Hu, Zeng and Zhu2014) rather than the shorter and broad lateral spines of K. lata, K. muricata, and Helmetia expansa Walcott, Reference Walcott1918 (Hou and Bergström, Reference Hou and Bergström1997; Briggs et al., Reference Briggs, Erwin, Collier and Clark1994; Losso et al., Reference Losso, Caron and Ortega-Hernández2025). Moreover, Dianhaia n. gen., Haifengella, and Rhombicalvaria exhibit significant morphological differences in the terminal pygidial spine. The length of the terminal spine relative to pygidial sagittal length of Dianhaia is much shorter than those of Haifengella and Rhombicalvaria.

The flagelliform antennae of Dianhaia n. gen., featuring long and robust spines and subrectangular podomeres, resemble those of trilobitomorphs such as Kuamaia from the Chengjiang biota (Hou, Reference Hou1987; Shu and Zhang, Reference Shu and Zhang1996; Chen, Reference Chen2004; O’Flynn et al., Reference O’Flynn, Williams, Liu, Hou, Guo and Edgecombe2025), as well as Kiisortoqia (Stein, Reference Stein2010), Siriocaris (Lagebro et al., Reference Lagebro, Stein and Peel2009), and Arthroaspis (Stein et al., Reference Stein, Budd, Peel and Harper2013) from the Sirius Passet biota of Greenland. These antennae have been compared to the frontal appendages of radiodonts (Stein, Reference Stein2010) and tentatively interpreted to have a predatory function, although specific functional evidence or modeling remains lacking. Other authors considered the morphology as antenniform and suggested possible raptorial and grasping functions (Zeng et al., Reference Zeng, Zhao, Niu, Zhu and Huang2020).

As in most trilobitomorphs, Dianhaia n. gen. is characterized by the homonomous post-antennal biramous appendages (Hou and Bergström, Reference Hou and Bergström1997; Chen, Reference Chen2004; Hou et al., Reference Hou, Siveter, Siveter, Aldridge, Cong, Gabbott, Ma, Purnell and Williams2017). Although the thoracic and pygidial appendages exhibit morphological differences in tomographic reconstruction (Fig. 3.6, 3.9), these differences likely result from the variable angles of burial. The endopodite morphology of Dianhaia n. gen. is also comparable to that of most trilobitomorphs, including trilobites and Kuamaia (Hou and Bergström, Reference Hou and Bergström1997; Ortega-Hernández et al., Reference Ortega-Hernández, Legg and Braddy2013; Zeng et al., Reference Zeng, Zhao, Yin and Zhu2017), consisting of six podomeres and a terminal claw. Compared to the helmetiids Kuamaia and Saperion, the endopodite endites of Dianhaia are more robust and bear clusters of sharp, elongated spines (Hou and Bergström, Reference Hou and Bergström1997; Edgecombe and Ramsköld, Reference Edgecombe and Ramsköld1999).

The exopodite of Dianhaia n. gen. is non-segmented and bears overlapping lamellae proximally and uniformly distributed fine setae along the distal margin, most closely resembling the exopodite of Kwanyinaspis (Zhang and Shu, Reference Zhang and Shu2005). However, the proximal part of the exopodite lobe in Dianhaia is broad and not constricted. In Kwanyinaspis, the lobe narrows rapidly along its proximal part, with this constricted region fringed by imbricated lamellae (Zhang and Shu, Reference Zhang and Shu2005).

Within Helmetiida, the exopodite morphologies have been reconstructed in Dianhaia n. gen., Kuamaia, and Saperion, but they display considerable variation. The exopodite lobe is undivided in Dianhaia, bipartite in Saperion, and tripartite in Kuamaia (Hou and Bergström, Reference Hou and Bergström1997; Edgecombe and Ramsköld, Reference Edgecombe and Ramsköld1999). Despite these differences in lobate structure, all three taxa developed imbricated lamellae along the proximal margin of exopodite lobe (Hou and Bergström, Reference Hou and Bergström1997; Edgecombe and Ramsköld, Reference Edgecombe and Ramsköld1999). Exopodite lamellae are a common character shared by most trilobitomorphs (Whittington, Reference Whittington1977; Ramsköld and Edgecombe, Reference Ramsköld and Edgecombe1996; Zhang and Shu, Reference Zhang and Shu2005; Zhang et al., Reference Zhang, Liu, Mai, Schmidt and Hou2024). However, the presence of exopodite lamellae might not be a synapomorphy of Trilobitomorpha, because no imbricated lamellae have been found from the exopodites of early-diverging taxa such as Squamacula and Thulaspis (Zhang et al., Reference Zhang, Han, Zhang, Liu and Shu2004; Berks et al., Reference Berks, Lunde Nielsen, Flannery-Sutherland, Thorshøj Nielsen, Park and Vinther2023).

Discussion

All phylogenetic results consistently resolved Dianhaia n. gen. within Helmetiidae. Only under concavity value k = 1, does Dianhaia have an unresolved placement within Helmetiidae (Fig. 5.1). Under Bayesian inference and parsimony analyses with concavity values k = 2–9, 10, 20, ∞, Dianhaia n. gen. is retrieved as the sister taxon to Haifengella (Fig. 5.1–5.4). Dianhaia + Haifengella is one of the latest-branching groups within Helmetiidae. Arthroaspis forms the sister taxon of the Helmetiida clade. However, under different models or character weighting settings, the internal relationships of Helmetiidae exhibit some variations.

Figure 5.

Phylogenetic reconstruction of Dianhaia heptacantha n. gen. n. sp. and the interrelationships of Helmetiida from parsimony or Bayesian analyses, with the non-helmetiid concilitergan Arthroaspis as the sister taxon of Helmetiida. (1–4) Strict consensus trees from parsimony analyses using implied or equal weighting of characters under various concavity values (k). Bootstrap, jackknife, and group present/contradicted supports are placed at the top left, bottom left, and middle right of nodes and are in regular, italics, and bold, respectively. (1) k = 1; (2) k = 2–4; (3) k = 5–9; (4) k = 10, 20, ∞; (5) 50% majority-rule consensus tree from Bayesian inference under the Mkv + gamma model. Taxa included in Figure 5 not otherwise mentioned in the text: Arthroaspis bergstroemi Stein et al., Reference Stein, Budd, Peel and Harper2013; Australimicola spriggi Paterson, García-Bellido, and Edgecombe, Reference Paterson, García-Bellido and Edgecombe2012; Campanamuta mantonae Budd, Reference Budd2011; Haifengella corona Zhao et al., Reference Zhao, Hu, Zeng and Zhu2014; Kwanyinaspis maotianshanensis Zhang and Shu, Reference Zhang and Shu2005; Rhombicalvaria acantha Hou, Reference Hou1987; Saperion glumaceum Hou, Ramsköld, and Bergström, Reference Hou, Ramsköld and Bergström1991; Skioldia aldna Hou and Bergström, Reference Hou and Bergström1997; Tegopelte gigas Simonetta and Delle Cave, Reference Simonetta and Delle Cave1975.

Five phylogenetic trees showing the evolutionary relationships of Dianhaia heptacantha and related Helmetiida taxa under different parsimony and Bayesian analysis parameters. See long description.
Figure 5. Long description

The figure consists of five panels numbered 1 through 5. Panels 1 to 4 are strict consensus trees from parsimony analyses with varying concavity values k. Panel 5 is a 50 percent majority-rule consensus tree from Bayesian inference.

Panel 1 k equals 1. Arthroaspis bergstroemi and Campanamuta mantonae are basal. Dianhaia heptacantha is nested within a clade containing Haifengella corona, Rhombicalvaria acantha, and Helmetia expansa. Saperion glumaceum and Tegopelte gigas form the most distal sister group.

Panel 2 k equals 2 to 4. Dianhaia heptacantha and Haifengella corona form a sister pair at the top of the tree. Saperion glumaceum and Tegopelte gigas are grouped in a separate lower clade with Skioldia aldna and Kuamaia lata.

Panel 3 k equals 5 to 9. The topology is similar to panel 2, with Dianhaia heptacantha and Haifengella corona as sister taxa. The lower clade now places Tegopelte gigas and Saperion glumaceum as sister taxa, with Skioldia aldna and Kuamaia lata as successive outgroups to them.

Panel 4 k equals 10, 20, and infinity. The structure remains consistent with panel 3, showing Dianhaia heptacantha and Haifengella corona as a terminal sister pair. Support values are indicated at nodes in regular, italics, and bold fonts.

Panel 5 Bayesian M k v plus gamma model. Arthroaspis bergstroemi is the outgroup. Dianhaia heptacantha and Haifengella corona are sister taxa in a clade that also includes Rhombicalvaria acantha and Helmetia expansa. A separate clade contains Tegopelte gigas, Saperion glumaceum, and Skioldia aldna, which is sister to a group containing Kuamaia lata and Kuamaia muricata.

Under low concavity value k = 1, which implies aggressive character weighting (Fig. 5.1), tree topology is different from the results under higher concavity values (see supplementary material for details). Dianhaia n. gen. and Haifengella form a polytomy with the Rhombicalvaria + Helmetia clade. Kuamaia muricata and K. lata, which are usually classified within Helmetiidae, have a closer relationship with Tegopeltidae. Australimicola is recovered as the earliest branching taxon to the (K. muricata + (K. lata + Tegopeltidae)) clade. This position of Australimicola is mainly caused by its suggested presence of an anterior sclerite (Paterson et al., Reference Paterson, García-Bellido and Edgecombe2012), but this placement hardly gains support from other characters because Australimicola has little similarity with helmetiids in trunk morphology. Kwanyinaspis forms the sister group of the Helmetiida clade, which is supported by their edge-to-edge pleural articulation of tergites. But with other character weighting settings, Kwanyinaspis is not allied with Helmetiida. With concavity value k = 1, Arthroaspis is recovered as the sister taxon of Kwanyinaspis + Helmetiida, and Campanamuta is the earliest branching taxon of the whole clade containing all the taxa above.

Under median concavity values of k = 2–9 and a strong but less aggressive weighting of characters (Fig. 5.2, 5.3), Kuamaia muricata is the earliest-branching species among Helmetiidae, but K. lata has a closer relationship with Tegopeltidae. Australimicola is no longer retrieved within Helmetiida. The Rhombicalvaria + Helmetia group is resolved as the sister group to Dianhaia + Haifengella. The position of Campanamuta shifts with increasing concavity values. Under concavity value k = 2–4, Campanamuta is the earliest branching taxon of the clade, whereas under concavity value k = 5–9, Campanamuta is not grouped with Helmetiida (Fig. 5.2, 5.3).

With high concavity values k = 10, 20, ∞, which stand for less downweighting to equal weighting of characters (Fig. 5.4), classical members of Helmetiidae, Kuamaia lata included, are recovered as a monophyletic group. Kuamaia lata is recovered as the earliest-branching taxon of Helmetiidae. Differing from results of lower concavity values (Fig. 5.1–5.3), the monophyletic Rhombicalvaria + Helmetia group changed into a paraphyletic lineage towards the group consisting of Dianhaia + Haifengella.

Under Bayesian inference (Fig. 5.5), the interrelationships between Dianhaia n. gen., Haifengella, Rhombicalvaria, and Helmetia are the same as the results from parsimony analyses using less downweighting to equal weighting of characters. As in the parsimony results with strong character weighting settings (Fig. 5.1, 5.2), Kuamaia lata is again retrieved as the sister group of Tegopeltidae. Kuamaia muricata, nevertheless, forms part of a trifurcating polytomy with the two clades respectively dominated by helmetiids and tegopeltids.

Based on the results above, under certain analytical parameters, Kuamaia lata and Tegopeltidae are grouped within the same clade. This suggests that the last common ancestor of Tegopeltidae may have possessed pleural or pygidial spines and distinct segmental boundaries. The two species of Kuamaia are respectively positioned at the earliest branches of Helmetiidae and Tegopeltidae, indicating that the two major groups of Helmetiida underwent two divergent evolutionary trajectories. One lineage, represented by Helmetiidae, evolved longer pleural and pygidial spines in more derived taxa. The other lineage, represented by Tegopeltidae, experienced a reduction of pleural or pygidial spines, along with thoracic tergites with a higher degree of fusion.

Conclusions

Dianhaia heptacantha n. gen. n. sp. represents a new genus and species of Helmetiida from the early Cambrian Chengjiang biota. The appendicular morphology of Dianhaia n. gen. differs from those previously described for other helmetiids. Phylogenetic analysis illuminates the internal evolutionary relationships within the helmetiids and resolves Dianhaia n. gen. and Haifengella as sister taxa. The discovery of Dianhaia n. gen. expands the taxonomic richness of helmetiids and further demonstrates the high morphological variation of appendages among Trilobitomorpha.

Acknowledgments

We are grateful to S. Wu for assistance in computed microtomographic scanning. This study was supported by the Natural Science Foundation of Jiangsu Province (BK20230110), the National Natural Science Foundation of China (42330209, 42272019), and the Youth Innovation Promotion Association of Chinese Academy of Sciences (2023322).

Author contribution

HZ and FZ designed the research. FZ and HZ collected and curated the fossil material. HZ prepared the specimens. YZ, HZ, YL, and FZ interpreted the fossil material. YZ and HZ photographed the specimens. YZ made the interpretive drawing and the reconstruction. YZ carried out the phylogenetic analysis. YZ wrote the paper under the supervision of HZ and with input from the other authors.

Competing interests

The authors declare none.

Data availability statement

Data available from the Science Data Bank digital repository: https://www.scidb.cn/s/U7fQNn.

Footnotes

Handling Editor: Lieberman, Bruce

References

Berks, H.O., Lunde Nielsen, M., Flannery-Sutherland, J., Thorshøj Nielsen, A., Park, T.Y.S., and Vinther, J., 2023, A possibly deep branching artiopodan arthropod from the lower Cambrian Sirius Passet Lagerstätte (North Greenland): Papers in Palaeontology, v. 9, e1495, https://doi.org/10.1002/spp2.1495.CrossRefGoogle Scholar
Briggs, D.E., Erwin, D.H., Collier, F.J., and Clark, C., 1994, The Fossils of the Burgess Shale: Washington, DC, Smithsonian Institution Press, 238 p.Google Scholar
Budd, G.E., 2011, Campanamuta mantonae gen. et. sp. nov., an exceptionally preserved arthropod from the Sirius Passet Fauna (Buen Formation, lower Cambrian, North Greenland): Journal of Systematic Palaeontology, v. 9, p. 217–260.10.1080/14772019.2010.492644CrossRefGoogle Scholar
Chen, J.Y., 2004, The Dawn of Animal World: Nanjing , Jiangsu Science and Technology Publishing House, 366 p.Google Scholar
Chen, X.H., Ortega-Hernández, J., Wolfe, J.M., Zhai, D.Y., Hou, X.G., Chen, A., Mai, H.J., and Liu, Y., 2019, The appendicular morphology of Sinoburius lunaris and the evolution of the artiopodan clade Xandarellida (Euarthropoda, early Cambrian) from South China: BMC Evolutionary Biology, v. 19, 165, https://doi.org/10.1186/s12862-019-1491-3.CrossRefGoogle ScholarPubMed
Edgecombe, G.D., and Ramsköld, L., 1999, Relationships of Cambrian Arachnata and the systematic position of Trilobita: Journal of Paleontology, v. 73, p. 263–287.10.1017/S0022336000027761CrossRefGoogle Scholar
Edgecombe, G.D., García-Bellido, D.C., and Paterson, J.R., 2025, A new xandarellid euarthropod from the lower Cambrian Emu Bay Shale, South Australia: Journal of Paleontology, v. 99, p. 905–913.10.1017/jpa.2025.10138CrossRefGoogle Scholar
Fortey, R.A., and Rushton, A.W.A., 2009, The Ordovician aglaspidid arthropod Tremaglaspis reconsidered: Memoirs of the Association of Australasian Palaeontologists, v. 37, p. 17–23.Google Scholar
Fu, D.J., Tong, G.H., Dai, T., Liu, W., Yang, Y.N., Zhang, Y., Cui, L.H., Li, L.Y., Yun, H., and Wu, Y., 2019, The Qingjiang biota—a Burgess Shale-type fossil Lagerstätte from the early Cambrian of South China: Science, v. 363, p. 1338–1342.10.1126/science.aau8800CrossRefGoogle ScholarPubMed
Goloboff, P.A., 1993, Estimating character weights during tree search: Cladistics, v. 9, p. 83–91.10.1111/j.1096-0031.1993.tb00209.xCrossRefGoogle ScholarPubMed
Goloboff, P.A., and Catalano, S.A., 2016, TNT version 1.5, including a full implementation of phylogenetic morphometrics: Cladistics, v. 32, p. 221–238.10.1111/cla.12160CrossRefGoogle ScholarPubMed
Goloboff, P.A., Farris, J.S., Källersjö, M., Oxelman, B., Ramıacuterez, M.J., and Szumik, C.A., 2003, Improvements to resampling measures of group support: Cladistics, v. 19, p. 324–332.10.1111/j.1096-0031.2003.tb00376.xCrossRefGoogle Scholar
Han, J., Shu, D.G., Zhang, Z.F., Liu, J.N., Zhang, X.L., and Yao, Y., 2006, Preliminary notes on soft-bodied fossil concentrations from the early Cambrian Chengjiang deposits: Chinese Science Bulletin, v. 51, p. 2482–2492.10.1007/s11434-005-2151-0CrossRefGoogle Scholar
Holmes, J.D., and Budd, G.E., 2022, Reassessing a cryptic history of early trilobite evolution: Communications Biology, v. 5, 1177, https://doi.org/10.1038/s42003-022-04146-6.CrossRefGoogle ScholarPubMed
Hou, X.G., 1987, Three new large arthropods from lower Cambrian, Chengjiang, eastern Yunnan: Acta Palaeontologica Sinica, v. 26, p. 272–285.Google Scholar
Hou, X.G., and Bergström, J., 1997, Arthropods of the lower Cambrian Chengjiang fauna, southwest China: Fossils and Strata, v. 45, p. 1–116.Google Scholar
Hou, X.G., Ramsköld, L., and Bergström, J., 1991, Composition and preservation of the Chengjiang fauna—a Lower Cambrian soft-bodied biota: Zoologica Scripta, v. 20, p. 395–411.Google Scholar
Hou, X.G., Siveter, D.J., Siveter, D.J., Aldridge, R.J., Cong, P.Y., Gabbott, S.E., Ma, X. Y., Purnell, M.A., and Williams, M., 2017, The Cambrian Fossils of Chengjiang, China: The Flowering of Early Animal Life: Kunming, John Wiley and Sons, 328 p.10.1002/9781118896372CrossRefGoogle Scholar
Hughes, N.C., 2007, The evolution of trilobite body patterning: Annual Review of Earth and Planetary Sciences, v. 35, p. 401–434.10.1146/annurev.earth.35.031306.140258CrossRefGoogle Scholar
Lagebro, L., Stein, M., and Peel, J.S., 2009, A new? lamellipedian arthropod from the early Cambrian Sirius Passet fauna of North Greenland: Journal of Paleontology, v. 83, p. 820–825.10.1666/09-011.1CrossRefGoogle Scholar
Lankester, E.R., 1904, The structure and classification of Arthropoda: Quarterly Journal of Microscopical Science, v. 47, p. 525–582.Google Scholar
Lerosey-Aubril, R., Ortega-Hernández, J., Kier, C., and Bonino, E., 2013, Occurrence of the Ordovician-type aglaspidid Tremaglaspis in the Cambrian Weeks Formation (Utah, USA): Geological Magazine, v. 150, p. 945–951.10.1017/S001675681300037XCrossRefGoogle Scholar
Lewis, P.O., 2001, A likelihood approach to estimating phylogeny from discrete morphological character data: Systematic Biology, v. 50, p. 913–925.10.1080/106351501753462876CrossRefGoogle ScholarPubMed
Losso, S.R., Caron, J.-B., and Ortega-Hernández, J., 2025, Helmetia expansa Walcott, 1918 revisited—new insights into the internal anatomy, moulting and phylogeny of Conciliterga: Journal of Systematic Palaeontology, v. 23, 2468195, https://doi.org/10.1080/14772019.2025.2468195.CrossRefGoogle Scholar
Lu, Y.H., 1940, On the ontogeny and phylogeny of Redlichia intermedia Lu (sp. nov): Bulletin of the Geological Society of China, v. 20, p. 333–342.Google Scholar
Mansuy, H., 1912, Étude Géologique du Yun-nan Oriental. IIe Partie. Paléontologie: Hanoi-Haiphong, Imprimerie d’Extrême-Orient, 146 p.Google Scholar
Novozhilov, N.I., 1960, Klass Merostomoidea Størmer, 1944, Chlenistonogie, Trilobitoobraznye i Rakoobraznye [Arthropoda, Trilobitomorpha and Crustacea]: Osnovy Paleontologii, p. 195–197.Google Scholar
O’Flynn, R.J., Williams, M., Liu, Y., Hou, X.G., Guo, J., and Edgecombe, G.D., 2025, The early Cambrian Kuamaia lata, an artiopodan euarthropod with a raptorial frontal appendage: Journal of Paleontology, v. 98, p. 808–820.10.1017/jpa.2024.33CrossRefGoogle Scholar
Ortega-Hernández, J., Legg, D.A., and Braddy, S.J., 2013, The phylogeny of aglaspidid arthropods and the internal relationships within Artiopoda: Cladistics, v. 29, p. 15–45.10.1111/j.1096-0031.2012.00413.xCrossRefGoogle ScholarPubMed
Paterson, J.R., García-Bellido, D.C., and Edgecombe, G.D., 2012, New artiopodan arthropods from the early Cambrian Emu Bay Shale Konservat-Lagerstätte of South Australia: Journal of Paleontology, v. 86, p. 340–357.10.1666/11-077.1CrossRefGoogle Scholar
Rambaut, A., Drummond, A.J., Xie, D., Baele, G., and Suchard, M.A., 2018, Posterior summarization in Bayesian phylogenetics using Tracer 1.7: Systematic Biology, v. 67, p. 901–904.10.1093/sysbio/syy032CrossRefGoogle ScholarPubMed
Ramsköld, L., and Edgecombe, G.D., 1996, Trilobite appendage structure—Eoredlichia reconsidered: Alcheringa, v. 20, p. 269–276.10.1080/03115519608619471CrossRefGoogle Scholar
Raymond, P.E., 1920, The appendages, anatomy, and relationships of trilobites: Connecticut Academy of Arts and Sciences, 169 p.10.5962/bhl.title.28256CrossRefGoogle Scholar
Ronquist, F., Teslenko, M., van der Mark, P., Ayres, D.L., Darling, A., Höhna, S., Larget, B., Liu, L., Suchard, M.A., and Huelsenbeck, J.P., 2012, MrBayes 3.2: efficient Bayesian phylogenetic inference and model choice across a large model space: Systematic Biology, v. 61, p. 539–542.10.1093/sysbio/sys029CrossRefGoogle ScholarPubMed
Shu, D.G., and Zhang, X.L., 1996, Kuamaia, an Early Cambrian predator from the Chengjiang Fossil Lagerstätte: Journal of Northwest University, Special Volume, p. 27–33.Google Scholar
Simonetta, A., and Delle Cave, L., 1975, The Cambrian non-trilobite arthropods from the Burgess Shale of British Columbia: a study of their comparative morphology, taxonomy and evolutionary significance: Palaeontographia Italica, v. 69, p. 1–37.Google Scholar
Stein, M., 2010, A new arthropod from the early Cambrian of North Greenland, with a ‘great appendage’-like antennula: Zoological Journal of the Linnean Society, v. 158, p. 477–500.10.1111/j.1096-3642.2009.00562.xCrossRefGoogle Scholar
Stein, M., Budd, G.E., Peel, J.S., and Harper, D.A., 2013, Arthroaspis n. gen., a common element of the Sirius Passet Lagerstätte (Cambrian, North Greenland), sheds light on trilobite ancestry: BMC Evolutionary Biology, v. 13, p. 1–34.10.1186/1471-2148-13-99CrossRefGoogle Scholar
Steiner, M., Zhu, M.Y., Weber, B., and Geyer, G., 2001, The lower Cambrian of eastern Yunnan: trilobite-based biostratigraphy and related faunas: Acta Palaeontologica Sinica, v. 40, p. 63–79.Google Scholar
Størmer, L., 1944, On the relationships and phylogeny of fossil and recent Arachnomorpha: a comparative study on Arachnida, Xiphosura, Eurypterida, Trilobita, and other fossil Arthropoda: Skrifter Utgitt av det Norske Videnskaps-Akademi i Oslo, Matematisk-Naturvidenskapelig Klasse, v. 5, p. 1–158.Google Scholar
Walch, J.E.I., 1771, Die Naturgeschichte der Versteinerungen zur Erläuterung der Knorrischen Sammlung von Merkwürdigkeiten der Natur: Nürnberg, Paul Jonathan Felstecker, 235 p.Google Scholar
Walcott, C.D., 1918, Geological explorations in the Canadian Rockies. Explorations and fieldwork of the Smithsonian Institution in 1917: Smithsonian Miscellaneous Collections, v. 68, p. 4–20.Google Scholar
Whittington, H.B., 1977, The middle Cambrian trilobite Naraoia, Burgess Shale, British Columbia: Philosophical Transactions of the Royal Society B, v. 280, p. 409–443.Google Scholar
Whittington, H.B., Chatterton, B.D.E., Speyer, S.E., Fortey, R.A., Owens, R.M., Chang, W.T., Dean, W.T., Jell, P.A., Laurie, J.R., and Palmer, A.R., 1997, Treatise on Invertebrate Paleontology, Part O, Arthropoda 1, Trilobita, Revised: Lawrence, KS, Geological Society of America and University of Kansas, 530 p.Google Scholar
Zeng, H., Zhao, F.C., Yin, Z.J., and Zhu, M.Y., 2017, Appendages of an early Cambrian metadoxidid trilobite from Yunnan, SW China support mandibulate affinities of trilobites and artiopods: Geological Magazine, v. 154, p. 1306–1328.10.1017/S0016756817000279CrossRefGoogle Scholar
Zeng, H., Zhao, F.C, Niu, K.C., Zhu, M.Y., and Huang, D.Y., 2020, An early Cambrian euarthropod with radiodont-like raptorial appendages: Nature, v. 588, p. 101–105.10.1038/s41586-020-2883-7CrossRefGoogle Scholar
Zhang, M.Y., Liu, Y., Mai, H.J., Schmidt, M., and Hou, X.G., 2024, Ventral morphology and ecological implications of Cindarella eucalla (Artiopoda, Xandarellida) from Chengjiang Biota, China: eLife, v. 13, RP100729, https://doi.org/10.7554/eLife.100729.1.Google Scholar
Zhang, X.L., and Shu, D.G., 2005, A new arthropod from the Chengjiang Lagerstätte, early Cambrian, southern China: Alcheringa, v. 29, p. 185–194.10.1080/03115510508619300CrossRefGoogle Scholar
Zhang, X.L., Han, J., Zhang, Z.F., Liu, H.Q., and Shu, D.G., 2004, Redescription of the Chengjiang arthropod Squamacula clypeata Hou and Bergström, from the lower Cambrian, south‐west China: Palaeontology, v. 47, p. 605–617.10.1111/j.0031-0239.2004.00363.xCrossRefGoogle Scholar
Zhao, F.C., Hu, S.X., Caron, J.-B., Zhu, M.Y., Yin, Z.J., and Lu, M., 2012, Spatial variation in the diversity and composition of the lower Cambrian (Series 2, Stage 3) Chengjiang biota, southwest China: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 346, p. 54–65.10.1016/j.palaeo.2012.05.021CrossRefGoogle Scholar
Zhao, F.C., Hu, S.X., Zeng, H., and Zhu, M.Y., 2014, A new helmetiid arthropod from the early Cambrian Chengjiang Lagerstätte, southwest China: Journal of Paleontology, v. 88, p. 367–370.10.1666/13-103CrossRefGoogle Scholar
Zhu, M.Y., Zhao, F.C., Zeng, H., Huang, D.,Li, Y., G.X., , and Luo, C., 2025, The Chengjiang Fauna: A Fossil Natural World Heritage Witnessed the Explosive Evolution of Life on Earth: Nanjing, Phoenix Science Press, 768 p.Google Scholar
Zhu, Y.Y., Zeng, H., Liu, Y., and Zhao, F.C., 2023, New artiopodan euarthropods from the Chengjiang fauna (Cambrian, Stage 3) at Malong, Yunnan, China: Acta Palaeontologica Polonica, v. 68, p. 427–440.10.4202/app.01080.2023CrossRefGoogle Scholar
Figure 0

Figure 1. Dianhaia heptacantha n. gen. n. sp. from the Cambrian Stage 3 Chengjiang biota, holotype NIGP 203984, part and counterpart. (1, 2, 4–9) Part, NIGP 203984a; (1) whole specimen; (2) interpretative drawing; (4) endopodite; (5) a thoracic biramous appendage; (6) exopodite; (7) setae on the exopodite; (8) spines on the pleural spine; (9) spines on the pygidium. (3) Counterpart, NIGP 203984b. Scale bars represent 5 mm (1, 2), 1 mm (3, 7), 2 mm (4–6, 8, 9). Abbreviations: as, anterior sclerite; ce, cephalic segment; cs, cephalic shield; cw, claw; ed, endite; en, endopodite; ex, exopodite; gs, genal spine; gn, gnathobase; hy, hypostome; lm, lamella; ls, lateral spine; ps, pleural spine; pt, protopodite; py, pygidium; sp, marginal spine; ts, terminal spine; T1–7, thoracic tergite 1–7; xs, setae on exopodite.Figure 1. long description.

Figure 1

Figure 2. Dianhaia heptacantha n. gen. n. sp. from the Cambrian Stage 3 Chengjiang biota, paratype NIGP 203985. (1) Whole specimen; (2) interpretative drawing; (3) pygidial segments; (4) cephalic and anterior thoracic segments with appendages; (5) marginal spines on the pygidial pleural spine; (6) marginal spines on the pygidium; (7) whole appendage; (8) endopodite; (9) setae on exopodite. Scale bars represent: 5 mm (1, 2), 2 mm (3), 1 mm (4–9). Abbreviations: as, anterior sclerite; en, endopodite; ex, exopodite; ls, lateral spine; ps, pleural spine; pt, protopodite; py, pygidium; sp, marginal spine; st, sternite; ts, terminal spine; T1–7, thoracic tergite 1–7; xs, setae on exopodite.Figure 2. long description.

Figure 2

Figure 3. Tomographic images of Dianhaia heptacantha n. gen. n. sp., holotype NIGP 203984. (1–6, 8) Maximum projection images; (7, 9) volume rendering images; (1–7) dorsal view; (8, 9) ventral view. (1) Whole specimen; (2) virtual section showing appendages from cephalon and anterior thorax; (3) setae on exopodite; (4) exopodite lamellae, under image stacking; (5) antenna; (6, 7) appendages from posterior thorax and pygidium; (8, 9) endopodite. Scale bars represent: 3 mm (1), 2 mm (2), 1 mm (3–9). Abbreviations: an, antenna; cw, claw; ed, endite; en, endopodite; ex, exopodite; gn, gnathobase; lm, lamella; pt, protopodite; sp, marginal spine; xs, setae on exopodite.Figure 3. long description.

Figure 3

Figure 4. Reconstruction of the helmetiid euarthropod Dianhaia heptacantha n. gen. n. sp. from the Cambrian Stage 3 Chengjiang biota. (1) Dorsal view; (2) ventral view. The reconstruction is based on the following figures: Tergites (Fig. 1.1); sternites (Fig. 2.1, 2.3); anterior sclerite (Figs. 1.3, 2.4); hypostome (Fig. 1.3); antennae (Fig. 3.5); protopodite (Fig. 3.6, 3.8); endopodite (Figs. 1.4, 3.6, 3.8); exopodite (Figs. 2.7, 3.3, 3.6); lamellae (Fig. 3.4). Morphology of the articular membrane and position of antennae are inferred. The number of antennal podomeres was referred from Kuamaia lata.Figure 4. long description.

Figure 4

Table 1. Morphological comparisons of HelmetiidaeTable 1. long description.

Figure 5

Figure 5. Phylogenetic reconstruction of Dianhaia heptacantha n. gen. n. sp. and the interrelationships of Helmetiida from parsimony or Bayesian analyses, with the non-helmetiid concilitergan Arthroaspis as the sister taxon of Helmetiida. (1–4) Strict consensus trees from parsimony analyses using implied or equal weighting of characters under various concavity values (k). Bootstrap, jackknife, and group present/contradicted supports are placed at the top left, bottom left, and middle right of nodes and are in regular, italics, and bold, respectively. (1) k = 1; (2) k = 2–4; (3) k = 5–9; (4) k = 10, 20, ∞; (5) 50% majority-rule consensus tree from Bayesian inference under the Mkv + gamma model. Taxa included in Figure 5 not otherwise mentioned in the text: Arthroaspis bergstroemi Stein et al., 2013; Australimicola spriggi Paterson, García-Bellido, and Edgecombe, 2012; Campanamuta mantonae Budd, 2011; Haifengella corona Zhao et al., 2014; Kwanyinaspis maotianshanensis Zhang and Shu, 2005; Rhombicalvaria acantha Hou, 1987; Saperion glumaceum Hou, Ramsköld, and Bergström, 1991; Skioldia aldna Hou and Bergström, 1997; Tegopelte gigas Simonetta and Delle Cave, 1975.Figure 5. long description.