Sunella

Sunella is an extinct genus of Cambrian stem group arthropod. It was named by Huo Shicheng in 1965. It is the type genus of the family Sunellidae. It has 4 species, including its type, S. grandis.

 Classification 
When it was first found by Huo Shicheng in 1965, Sunella was thought to be an Ostracod-like arthropod; then, in later studies it was thought to be an arthropod of uncertain affinities; then it was interpreted as a bradoriid and then as again an arthropod of uncertain affinities; then as a species of Isoxys along with other Sunellids in Vannier & Chen 2000; in later studies such as Zhang and Shu, 2007 and Sun et. al. 2021 it was yet again thought to be an arthropod of uncertain affinities possibly related to Tuzoia and Silesicaris, a relationship that was later disproved due to the fact that Silesicaris was reassigned to Thylacocephala and in 2022 Tuzoia was reassigned to Hymenocarina based on newly described soft parts showing that the similarities between the carapace shape between Isoxys and Sunella was only superficial; and then in Sun et al. 2021 it was again considered an arthropod of uncertain affinities, though similarities with Isoxys were noted and a relationship with Isoxys was suggested, as in Zhang and Shu, 2007, but due to limited preservation of soft tissue, a the relationships of Sunella remained uncertain; in 2025 it was recovered as a sister group to Isoxys by Collantes & Pates, 2025; which in turn makes Sunella an upper stem group (ancestral) arthropod and among the most ancestral  Deuteropods.


 Species 
Sunella grandis (Huo, 1965) is the type species of Sunella.Zhang, Xingliang; Shu, Degan (2007). "Soft anatomy of sunellid arthropods from the Chengjiang Lagerstutte, Lower Cambrian of southwest China". Journal of Paleontology. 81 (6): 1412–1422. Bibcode:2007JPal...81.1412Z. doi:10.1666/06-031R.1.L.m, Melnikova (1998). "REVISION OF SOME CAMBRIAN BRADORIIDS (CRUSTACEA) FROM THE SIBERIAN PLATFORM". Paleontologicheskii Zhurnal. ISSN 0031-031X. Possible sexual dimorphism (when individuals of a species of different sexes are differentiated) is known.Collantes, Luis; Pates, Stephen (2025). "Isoxys carbonelli and the palaeoenvironmental disparity of Isoxys during Cambrian Stage 3". Historical Biology: 1–9. doi:10.1080/08912963.2025.2529395. ISSN 0891-2963.

 Synonyms 

 Sunella nanchengensis (Huo, 1965)
 Luella (Huo, 1965)
 Chiella (Huo, 1965)

 Sunella nanchengensis 
Sunella nanchengensis (Huo, 1965) is a possible sexual dimorph of S. grandis and is now thought to be a synonym of S. grandis.Zhang, Xingliang; Shu, Degan (2007). "Soft anatomy of sunellid arthropods from the Chengjiang Lagerstutte, Lower Cambrian of southwest China". Journal of Paleontology. 81 (6): 1412–1422. Bibcode:2007JPal...81.1412Z. doi:10.1666/06-031R.1.Collantes, Luis; Pates, Stephen (2025). "Isoxys carbonelli and the palaeoenvironmental disparity of Isoxys during Cambrian Stage 3". Historical Biology: 1–9. doi:10.1080/08912963.2025.2529395. ISSN 0891-2963.

 Sunella shensiella 
Sunella shensiella (Huo,1965) is the only species of Sunella apart from S. grandis that is not considered a synonym of S. grandis or has been moved to its own genus.Zhang, Xingliang; Shu, Degan (2007). "Soft anatomy of sunellid arthropods from the Chengjiang Lagerstutte, Lower Cambrian of southwest China". Journal of Paleontology. 81 (6): 1412–1422. Bibcode:2007JPal...81.1412Z. doi:10.1666/06-031R.1.Sun, Ao; Cong, Liu; Ma, Jiaxin; Fu, Dongjing. "Taxonomy and ontogeny of bivalved arthropods from the lower member of the Shuijingtuo Formation, Series 2 and Stage 3, Eastern Three Georges Area, South China". Acta Palaeontologica Sinica. doi:10.19800/j.cnki.aps.2021019. Probable sexual dimorphism has been observed. It is the only species where soft parts are known.Collantes, Luis; Pates, Stephen (2025). "Isoxys carbonelli and the palaeoenvironmental disparity of Isoxys during Cambrian Stage 3". Historical Biology: 1–9. doi:10.1080/08912963.2025.2529395. ISSN 0891-2963.

 Caudicaella (Sunella) bispinata 
A species that used to belong to Sunella, S. bispinata, and was moved to a new genus, Caudicaella (Sun et al. 2021) as Caudicaella bispinata (Cui and Huo, 1990). Synonyms include Isoxys bispinata (Zhang et al., 2018) (not to be confused with Isoxys bispinatus) Isoxys sp. (Sun et al. 2021) (for the specimens from the Heatherdale shale, not the Shuijingtuo formation)

 Tuzoia? (Sunella) parva 
One former species is Sunella parva (Melnikova, 1988),L.m, Melnikova (1998). "REVISION OF SOME CAMBRIAN BRADORIIDS (CRUSTACEA) FROM THE SIBERIAN PLATFORM". Paleontologicheskii Zhurnal. ISSN 0031-031X. which may be the larval form of a new species of Tuzoia,Izquierdo-López, Alejandro; Caron, Jean-Bernard (December 2022). "The problematic Cambrian arthropod Tuzoia and the origin of mandibulates revisited". Royal Society Open Science. 9 (12) 220933. Bibcode:2022RSOS....920933I. doi:10.1098/rsos.220933. ISSN 2054-5703. PMC 9727825. PMID 36483757.Sun, Ao; Cong, Liu; Ma, Jiaxin; Fu, Dongjing. "Taxonomy and ontogeny of bivalved arthropods from the lower member of the Shuijingtuo Formation, Series 2 and Stage 3, Eastern Three Georges Area, South China". Acta Palaeontologica Sinica. doi:10.19800/j.cnki.aps.2021019. which was found not to be a species of  Sunella by Melnikova 1998 and may need to be assigned to its own genus.Zhang, Xingliang; Shu, Degan (2007). "Soft anatomy of sunellid arthropods from the Chengjiang Lagerstutte, Lower Cambrian of southwest China". Journal of Paleontology. 81 (6): 1412–1422. Bibcode:2007JPal...81.1412Z. doi:10.1666/06-031R.1. It has also been suggested to be a bradoriid (Melnikova, 1998)

 Synonyms 
Sunellidae, which Sunella belongs to originally included two other genera, Chiella (Huo, 1965) and Luella (Huo, 1965),Huo, Shicheng (1965). "The Early Cambrian ostracods from Shaanxi and Yunnan". Acta Palaeontologica Sinica (in Chinese and English). 13.
Category:CS1 Chinese-language sources (zh) Chiella was later considered a separate species within Sunella,Zhang, Xingliang; Shu, Degan (2007). "Soft anatomy of sunellid arthropods from the Chengjiang Lagerstutte, Lower Cambrian of southwest China". Journal of Paleontology. 81 (6): 1412–1422. Bibcode:2007JPal...81.1412Z. doi:10.1666/06-031R.1. but after Huo & Shu, 1985 Chiella was considered a junior synonym of Sunella and after Zhang & Shu, 2007 Luella was considered a possible sexual dimorph of Sunella.Huo, Shicheng; Shu, Degan (January 1985). Cambrian bradoriids of South China (in Chinese). China: Northwest University Press.
Category:CS1 Chinese-language sources (zh)Collantes, Luis; Pates, Stephen (2025). "Isoxys carbonelli and the palaeoenvironmental disparity of Isoxys during Cambrian Stage 3". Historical Biology: 1–9. doi:10.1080/08912963.2025.2529395. ISSN 0891-2963.

 Distribution 
Sunella fossils have been found in the Chengjiang biota (exact locality cannot be determined;Zhang, Xingliang; Shu, Degan (2007). "Soft anatomy of sunellid arthropods from the Chengjiang Lagerstutte, Lower Cambrian of southwest China". Journal of Paleontology. 81 (6): 1412–1422. Bibcode:2007JPal...81.1412Z. doi:10.1666/06-031R.1. dated to no older than 518 Ma),"Chengjiang Maotianshan Shales". www.fossilmuseum.net. Archived from the original on 9 March 2021. Retrieved 24 September 2025. the Shuijingtuo formation (dated to around 526.5 Ma),Cui, Zhilin; Huo, Shicheng (1990). "New discoveries of Lower Cambrian crustacean fossils from western Hubei". Acta Palaeontologica Sinica (in Chinese and English). 29 (3): 321–330.
Category:CS1 Chinese-language sources (zh)Ma, Jiaxin; Lin, Weiliang; Liu, Cong; Sun, Ao; Wu, Yu; Wu, Yuheng; Fu, Dongjing (6 July 2021). "A new bivalved arthropod from the Cambrian (Stage 3) Qingjiang biota expands the palaeogeographical distribution and increases the diversity of Tuzoiidae". Journal of the Geological Society. 179 (1) jgs2020–229. doi:10.1144/jgs2020-229.Sun, Ao; Cong, Liu; Ma, Jiaxin; Fu, Dongjing. "Taxonomy and ontogeny of bivalved arthropods from the lower member of the Shuijingtuo Formation, Series 2 and Stage 3, Eastern Three Georges Area, South China". Acta Palaeontologica Sinica. doi:10.19800/j.cnki.aps.2021019. the Qingjiang biota (dated to ~518 ma), the Niutitang formation ( generally Meishucunian (Cambrian Stage 2) to Nangaoan (Cambrian Stage 3) but may be up to as old as the Fortunian in some sections) and the Guojiaba formation (tentatively assigned to Cambrian Stage 3), all of which are in China. Similiar fossils have been found at other formations in China but they are relatively uncommon and poorly studied and therefore cannot be confidently assigned to this genus or even Sunellidae. The former species Caudicaella bispinata is also known from the Heatherdale shale in Australia.Collantes, Luis; Pates, Stephen (2025). "Isoxys carbonelli and the palaeoenvironmental disparity of Isoxys during Cambrian Stage 3". Historical Biology: 1–9. doi:10.1080/08912963.2025.2529395. ISSN 0891-2963.Chen, Fei-Yang; Betts, Marissa J.; Zhang, Zhi-Liang; Brock, Glenn A. (2025-06-01). "The bivalved arthropod Caudicaella aff. bispinata from the Heatherdale Shale (Cambrian Stage 3), South Australia". Palaeoworld. 34 (3): 100882. Bibcode:2025Palae..3400882C. doi:10.1016/j.palwor.2024.09.006. ISSN 1871-174X.

Usually the only part of Sunella that is found is the shell, but rarely (only twenty-two times in Sunella cf. shensiella and only six in the related Combinivalvula chenjiangensis) soft parts are also found. When this occurs, the carapace usually adopts a "butterfly" position, possibly due to the decay of the shell muscles that hold it together.Zhang, Xingliang; Shu, Degan (2007). "Soft anatomy of sunellid arthropods from the Chengjiang Lagerstutte, Lower Cambrian of southwest China". Journal of Paleontology. 81 (6): 1412–1422. Bibcode:2007JPal...81.1412Z. doi:10.1666/06-031R.1. Only the soft parts of Sunella cf. shensiella and the related Combinivalvula chenjiangensis (Hou, 1987)Williams, Mark; Siveter, David J.; Peel, John S. (1996). "Isoxys (Arthropoda) from the Early Cambrian Sirius Passet Lagerstätte, North Greenland". Journal of Paleontology. 70 (6): 947–954. Bibcode:1996JPal...70..947W. doi:10.1017/S0022336000038646. ISSN 0022-3360. JSTOR 1306499. have been preserved.Collantes, Luis; Pates, Stephen (2025). "Isoxys carbonelli and the palaeoenvironmental disparity of Isoxys during Cambrian Stage 3". Historical Biology: 1–9. doi:10.1080/08912963.2025.2529395. ISSN 0891-2963.

Sunella grandis had a bivalved elongate roughly semicircular shell with an anterodorsal sulcus and short spines,Hou, Xian-guang (1987). "EARLY CAMBRIAN LARGE BIVALVED ARTHROPODS FROM CHENGJIANG, EASTERN YUNNAN". Acta Palaeontologica Sinica. 26 (3): 272–285. Archived from the original on 2023-03-02. Retrieved 2025-10-10. a typical bodyplan for a Sunellid,Chen, Fei-Yang; Betts, Marissa J.; Zhang, Zhi-Liang; Brock, Glenn A. (2025-06-01). "The bivalved arthropod Caudicaella aff. bispinata from the Heatherdale Shale (Cambrian Stage 3), South Australia". Palaeoworld. 34 (3): 100882. Bibcode:2025Palae..3400882C. doi:10.1016/j.palwor.2024.09.006. ISSN 1871-174X.Sun, Ao; Cong, Liu; Ma, Jiaxin; Fu, Dongjing. "Taxonomy and ontogeny of bivalved arthropods from the lower member of the Shuijingtuo Formation, Series 2 and Stage 3, Eastern Three Georges Area, South China". Acta Palaeontologica Sinica. doi:10.19800/j.cnki.aps.2021019.Collantes, Luis; Pates, Stephen (2025). "Isoxys carbonelli and the palaeoenvironmental disparity of Isoxys during Cambrian Stage 3". Historical Biology: 1–9. doi:10.1080/08912963.2025.2529395. ISSN 0891-2963.Zhang, Xingliang; Shu, Degan (2007). "Soft anatomy of sunellid arthropods from the Chengjiang Lagerstutte, Lower Cambrian of southwest China". Journal of Paleontology. 81 (6): 1412–1422. Bibcode:2007JPal...81.1412Z. doi:10.1666/06-031R.1. while S. cf. shensiella had a more oval shaped shell, shorter cardinal spines and an anterodorsal sulcus pointing at a slightly lower angle. Both species have shorter cardinal spines than Caudicaella bispinata also Caudicaella bispinata is more similar to Isoxys than other sunellids which led to its assignment to Isoxys in Zhang et al. 2018. Jinningella differs from Sunella by the presence of anterodorsal nodes. possible  sexual dimorphism has been recorded in both species.

The carapace of S. grandis is typically 6.5-8.5 mm.Zhang, Xingliang; Shu, Degan (2007). "Soft anatomy of sunellid arthropods from the Chengjiang Lagerstutte, Lower Cambrian of southwest China". Journal of Paleontology. 81 (6): 1412–1422. Bibcode:2007JPal...81.1412Z. doi:10.1666/06-031R.1.Collantes, Luis; Pates, Stephen (2025). "Isoxys carbonelli and the palaeoenvironmental disparity of Isoxys during Cambrian Stage 3". Historical Biology: 1–9. doi:10.1080/08912963.2025.2529395. ISSN 0891-2963.Sun, Ao; Cong, Liu; Ma, Jiaxin; Fu, Dongjing. "Taxonomy and ontogeny of bivalved arthropods from the lower member of the Shuijingtuo Formation, Series 2 and Stage 3, Eastern Three Georges Area, South China". Acta Palaeontologica Sinica. doi:10.19800/j.cnki.aps.2021019. The largest specimen is over 15 mm (1.5 cm)(the largest recorded for a sunellid), while Combinivalvula and Jinningella reached roughly 10 mm (1 cm) and Caudicaella typically reached 10–12 mm (1-1.2 cm) due to its long  spines compared to other sunellids.Chen, Fei-Yang; Betts, Marissa J.; Zhang, Zhi-Liang; Brock, Glenn A. (2025-06-01). "The bivalved arthropod Caudicaella aff. bispinata from the Heatherdale Shale (Cambrian Stage 3), South Australia". Palaeoworld. 34 (3): 100882. Bibcode:2025Palae..3400882C. doi:10.1016/j.palwor.2024.09.006. ISSN 1871-174X. In comparison to other bivalved arthropods of the Cambrian, sunellids where medium sized, larger than the bradoriids, which rarely reached above 10 mm (1 cm) and smaller than the Isoxyida which where often at least a few centimeters long with the exception of the dwarf I. carbonelli which grew to 11 mm (1.1 cm) and Surusicaris which grew to 14 mm (1.4 cm).

 Distinguishing from similar arthropods 
Sunella can be distinguished from Isoxys by the presence of an anterodorsal sulcus, shorter cardinal spines and different carapace shapes.Zhang, Xingliang; Shu, Degan (2007). "Soft anatomy of sunellid arthropods from the Chengjiang Lagerstutte, Lower Cambrian of southwest China". Journal of Paleontology. 81 (6): 1412–1422. Bibcode:2007JPal...81.1412Z. doi:10.1666/06-031R.1.Collantes, Luis; Pates, Stephen (2025). "Isoxys carbonelli and the palaeoenvironmental disparity of Isoxys during Cambrian Stage 3". Historical Biology: 1–9. doi:10.1080/08912963.2025.2529395. ISSN 0891-2963. Sunella be distinguished from the isoxyid Surusicaris by the lack of an anterodorsal sulcus and the lack of cardinal spines.Bradoriids, which share the possession of an anterodorsal sulcus (leading to the former assignment of Sunella to Bradoriida)Xian-Guang, Hou (January 1999). "New rare bivalved arthropods from the Lower Cambrian Chengjiang fauna, Yunnan, China". Journal of Paleontology. 73 (1): 102–116. Bibcode:1999JPal...73..102X. doi:10.1017/S002233600002758X. ISSN 0022-3360. JSTOR 1306748 – via JSTOR.Huo, Shicheng; Shu, Degan (January 1985). Cambrian bradoriids of South China (in Chinese). China: Northwest University Press.
Category:CS1 Chinese-language sources (zh)Jones, P.J.; McKenzie, K.G. (1980-01-01). "Queensland Middle Cambrian Bradoriida (Crustacea): new taxa, palaeobiogeography and biological affinities". Alcheringa: An Australasian Journal of Palaeontology. 4 (3): 203–225. Bibcode:1980Alch....4..203J. doi:10.1080/03115518008618932. ISSN 0311-5518.Williams, Mark; Siveter, David J.; Popov, Leonid E.; Vannier, Jean M. C. (2007-05-14). "Biogeography and affinities of the bradoriid arthropods: Cosmopolitan microbenthos of the Cambrian seas". Palaeogeography, Palaeoclimatology, Palaeoecology. 248 (1): 202–232. Bibcode:2007PPP...248..202W. doi:10.1016/j.palaeo.2006.12.004. ISSN 0031-0182.Melnikova, L. M. (1988). "Some Bradoriids (Crustacea) from the Botomian stage of Eastern Transbaikalia". Paleontologicheskii Zhurnal.L.m, Melnikova (1998). "REVISION OF SOME CAMBRIAN BRADORIIDS (CRUSTACEA) FROM THE SIBERIAN PLATFORM". Paleontologicheskii Zhurnal. ISSN 0031-031X.  can be distinguished from Sunella by the possession of cardinal spines.

 Soft anatomy 
The soft parts of S. cf. shensiella and Combinivalvula chengjiangensis show that Sunellids had non-biomineralized biramous limbs similar to the related Isoxyidae and a clearly segmented trunk.Zhang, Xingliang; Shu, Degan (2007). "Soft anatomy of sunellid arthropods from the Chengjiang Lagerstutte, Lower Cambrian of southwest China". Journal of Paleontology. 81 (6): 1412–1422. Bibcode:2007JPal...81.1412Z. doi:10.1666/06-031R.1.Chen, Fei-Yang; Betts, Marissa J.; Zhang, Zhi-Liang; Brock, Glenn A. (2025-06-01). "The bivalved arthropod Caudicaella aff. bispinata from the Heatherdale Shale (Cambrian Stage 3), South Australia". Palaeoworld. 34 (3): 100882. Bibcode:2025Palae..3400882C. doi:10.1016/j.palwor.2024.09.006. ISSN 1871-174X.Collantes, Luis; Pates, Stephen (2025). "Isoxys carbonelli and the palaeoenvironmental disparity of Isoxys during Cambrian Stage 3". Historical Biology: 1–9. doi:10.1080/08912963.2025.2529395. ISSN 0891-2963.S. cf. shensiella and the related Combinivalvula chenjiangensis preserve a possible median eye.Fu, Dongjing; Zhang, Xingliang (2011). "A New Arthropod Jugatacaris Agilis N. Gen. N. Sp. from the Early Cambrian Chengjiang Biota, South China". Journal of Paleontology. 85 (3): 567–586. Bibcode:2011JPal...85..567F. doi:10.1666/09-173.1. ISSN 0022-3360. JSTOR 23020192. Neither the cephalic appendages nor proximal portions of trunk limbs as found in the related Isoxyidae are known.

Category:Arthropods
Category:Cambrian
Category:Cambrian life
Category:Pages with unreviewed translations