Sunella

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Sunella
Temporal range: Cambrian stage 2–Cambrian stage 3
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[1] [2] [3] [4] Some specimens may be as old as 531.94 ma. [5] [1]
Sunella grandis.jpg
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Animalia
Phylum: Arthropoda
Order:† Isoxyida
Family:† Sunellidae
Genus:† Sunella
Huo, 1965 [3] [6]
Type species
†Sunella grandis
Huo, 1965 [3] [6]
Species

see text

Synonyms

see text

Sunella is an extinct genus of Cambrian stem group arthropod. [2] [7] It was described by Huo Shicheng in 1965. [8] [6] [3] [9] [4] [10] It is the type genus of the family Sunellidae. [3] [4] [6] [10] Its type species is S. grandis. [2] [3] [6] [4] It was assigned to the order Isoxyida by Collantes & Pates, 2025. [2]

Contents

Classification

In the original description (Huo, 1965), Sunella was described as an Ostracod-like arthropod; [11] [6] [3] then as an arthropod of uncertain affinities; [3] [2] [9] [4] then as a bradoriid [11] [12] [13] [14] [8] [15] and then as an arthropod of uncertain affinities; [11] [16] then as a species of Isoxys along with other Sunellids in Vannier & Chen 2000; [9] [2] [3] [17] in later studies such as Zhang and Shu, 2007 and Sun et. al. 2021 [3] [4] it was classified as an arthropod of uncertain affinities possibly related to Tuzoia and Silesicaris, [3] a relationship that was later rejected due to the fact that Silesicaris was reassigned to Thylacocephala and in 2022 Tuzoia was reassigned to Hymenocarina; [18] [3] [16] Sun et al. 2021 it was again considered an arthropod of uncertain affinities, [4] though similarities with Isoxys were noted and a relationship with Isoxys was suggested, as in Zhang and Shu, 2007; [3] [4] it was not until 2025 that it was formally assigned to Isoxyida by Collantes & Pates, 2025; which in turn makes Sunella an upper stem group arthropod among the most basal Deuteropods. [2] [19]

Sunella is related to Isoxys (Walcott, 1890), a reconstruction of the species I. volucris (Williams et. al. 1996) from the Sirius Passet is pictured above. Isoxys volucris.png
Sunella is related to Isoxys (Walcott, 1890), a reconstruction of the species I. volucris (Williams et. al. 1996) from the Sirius Passet is pictured above.

Species

Species of Sunella include:

A species that previously belonged to Sunella, S. bispinata, [10] [28] and was moved to it’s own genus, Caudicaella (Sun et al. 2021) [4] [2] as Caudicaella bispinata (Cui and Huo, 1990). [4] [2] [10] [9] Synonyms include Isoxys bispinata (Zhang et al., 2018) [29] (not to be confused with Isoxys bispinatus) [2] [9] Isoxys sp.(Sun et al. 2021) (for the specimens from the Heatherdale shale, not the Shuijingtuo formation) [9] [4]

One former species is Sunella parva (Melnikova, 1988), [15] [8] [30] which may be the larval form of a new species of Tuzoia [18] [4] and was rejected from Sunella by Melnikova 1998 [8] [15] [30] and may need to be assigned to its own genus. [15] [3] [18] [30] It has also been suggested to be a Bradoriid. [15] [8]

Synonyms

Sunellidae, which Sunella belongs to originally included two other genera, Chiella (Huo, 1965) and Luella (Huo, 1965), [6] but after Huo & Shu, 1985Chiella was considered a junior synonym of Sunella [3] and after Zhang & Shu, 2007Luella was considered a probable sexual dimorph of Sunella. [3] [12] [2]

Distribution

Sunella fossils have been found in the Chengjiang biota (exact locality cannot be determined; [3] dated to no older than 518 Ma), [31] [26] the Shuijingtuo formation (dated to around 526.5 Ma), [32] [10] [30] [4] [33] the Qingjiang biota (dated to ~518 ma), [27] 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) [1] [5] and the Guojiaba formation (tentatively assigned to Cambrian Stage 3), [3] [34] all of which are in China. [3] [4] 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. [3] The former species Caudicaella bispinata is also known from the Heatherdale shale in Australia. [2] [9]

Preservation

Usually the only part of Sunella that is preserved is the carapace, but rarely (only twenty-two times in Sunella cf. shensiella and only six in the related Combinivalvula chenjiangensis) soft tissue is also preserved. When this occurs, the carapace usually adopts a "butterfly" position, possibly due to the decay of the adductor muscles that hold it together. [3] Only the soft parts of Sunella cf. shensiella and the related Combinivalvula chenjiangensis (Hou, 1987) [35] [36] [16] have been preserved. [3] [2]

Morphology

Carapace

Sunella grandis had a bivalved [37] roughly semicircular carapace with an anterodorsal sulcus and cardinal spines, [35] a typical bodyplan for a Sunellid, [9] [4] [2] [3] while S. cf. shensiella had a more oval shaped carapace, shorter cardinal spines and an anterodorsal sulcus pointing at a slightly lower angle. [3] [4] Both species have shorter cardinal spines than Caudicaella bispinata also Caudicaella bispinata had a longer carapace in relation to the height of the carapace relative to S. grandis. [3] [4] [9] Probable Sexual dimorphism has been recorded in both species. [3] [2] [4] The carapace of S.grandis is typically 6.5-8.5 mm. [3] [4] The largest specimen is 15mm, which is the largest recorded for a Sunellid. [4] [2] [9]

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. [3] [9] [2] The related Combinivalvula chenjiangensis also preserves a possible median eye. [3] [36] Neither the cephalic appendages nor proximal portions of trunk limbs as found in the related Isoxyidae are known. [2] [3]

References

  1. 1 2 3 Zhao, M.-S.; Wang, Y.; Tian, J. -C.; Lei, L. -F. (October 2013). "A sedimentary environment analysis of black shales based on fossil assemblage characteristics:A case study of cambrian niutitang formation in Changyang area, western Hubei". Geology in China. 40(5):1484-1492 – via Researchgate.net.
  2. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Collantes, Luis; Pates, Stephen (2025). "Isoxys carbonelli and the palaeoenvironmental disparity of Isoxys during Cambrian Stage 3". Historical Biology. 0: 1–9. doi: 10.1080/08912963.2025.2529395 . ISSN   0891-2963.
  3. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 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.
  4. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 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.
  5. 1 2 "Niutitang Formation". chinalex.geolex.org. Retrieved 2025-09-27.
  6. 1 2 3 4 5 6 7 8 9 10 11 12 Huo, Shicheng (1965). "The Early Cambrian ostracods from Shaanxi and Yunnan". Acta Palaeontologica Sinica (in Chinese and English). 13 (1965).
  7. ↑ Zhang, Lei; Chang, Shan; Khan, Maliha Zareen; Feng, Qinglai; Luo, Cui; Steiner, Michael; Forel, Marie-Béatrice; Liu, Kai; Clausen, Sébastien (October 2020). "Influence of palaeo-redox and diagenetic conditions on the spatial distribution of Cambrian biotas: A case study from the upper Shuijingtuo Formation (Cambrian Series 2, Stage 3), Three Gorges area of South China". Palaeogeography, Palaeoclimatology, Palaeoecology. doi:10.1016/j.palaeo.2020.109696.
  8. 1 2 3 4 5 Melnikova, L. M. (1988). "Some Bradoriids (Crustacea) from the Botomian stage of Eastern Transbaikalia". Paleontologicheskii Zhurnal.
  9. 1 2 3 4 5 6 7 8 9 10 11 12 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. doi:10.1016/j.palwor.2024.09.006. ISSN   1871-174X.
  10. 1 2 3 4 5 6 Cui, Zhilin; Huo, Shicheng (1990). "New discoveries of Lower Cambrian crustacean fossils from western Hubei". Acta Palaeontologica Sinica (in Chinese and English). 29(3) 1990: 321-330.
  11. 1 2 3 Xian-Guang, Hou (January 1999). "New rare bivalved arthropods from the Lower Cambrian Chengjiang fauna, Yunnan, China". Journal of Paleontology. 73 (1): 102–116. doi:10.1017/S002233600002758X. ISSN   0022-3360 – via JSTOR.
  12. 1 2 Huo, Shicheng; Shu, Degan (January 1985). Cambrian bradoriids of South China (in Chinese). China: Northwest University press (published 1985).
  13. ↑ 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. doi:10.1080/03115518008618932. ISSN   0311-5518.
  14. ↑ 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. doi:10.1016/j.palaeo.2006.12.004. ISSN   0031-0182.
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  16. 1 2 3 4 5 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. ISSN   0022-3360.
  17. ↑ Vannier, Jean; Chen, Jun-Yuan (2000). "The Early Cambrian colonization of pelagic niches exemplified by Isoxys (Arthropoda)". Lethaia. 33 (4): 295–311. doi:10.1080/002411600750053862. ISSN   1502-3931.
  18. 1 2 3 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.
  19. ↑ Zhang, Caixia; Liu, Yu; Ortega-Hernández, Javier; Wolfe, Joanna M.; Jin, Changfei; Mai, Huijuan; Hou, Xianguang; Guo, Jin; Zhai, Dayou (2023-04-26). "Three-dimensional morphology of the biramous appendages in Isoxys from the early Cambrian of South China, and its implications for early euarthropod evolution". Proceedings. Biological Sciences. 290 (1997) 20230335. doi:10.1098/rspb.2023.0335. ISSN   1471-2954. PMC   10113025 . PMID   37072042.
  20. ↑ Paterson, John R.; García-Bellido, Diego C.; Edgecombe, Gregory D. (2012). "New Artiopodan Arthropods from the Early Cambrian Emu Bay Shale Konservat-Lagerstätte of South Australia". Journal of Paleontology. 86 (2): 340–357. ISSN   0022-3360.
  21. ↑ "PBDB". paleobiodb.org. Archived from the original on 2022-02-03. Retrieved 2025-10-11.
  22. ↑ "PBDB Taxon". paleobiodb.org. Archived from the original on 2025-02-07. Retrieved 2025-10-11.
  23. ↑ Park, Tae-Yoon S.; Nielsen, Morten Lunde; Parry, Luke A.; Sørensen, Martin Vinther; Lee, Mirinae; Kihm, Ji-Hoon; Ahn, Inhye; Park, Changkun; de Vivo, Giacinto; Smith, M. Paul; Harper, David A. T.; Nielsen, Arne T.; Vinther, Jakob (2024-01-05). "A giant stem-group chaetognath". Science Advances. 10 (1): eadi6678. doi:10.1126/sciadv.adi6678. ISSN   2375-2548. PMC   10796117 . PMID   38170772.{{cite journal}}: CS1 maint: article number as page number (link)
  24. ↑ Nielsen, Morten Lunde; Lee, Mirinae; Wilby, Philip R.; Park, Tae-Yoon S.; Nielsen, Arne T.; Vinther, Jakob (2025). "Negative ontogenetic allometry of cardinal spines in the early Cambrian arthropod Isoxys volucris indicates their defensive function". Palaeontology. 68 e7107 (4). doi:10.1111/pala.70017. ISSN   1475-4983.
  25. ↑ Daley, Allison C.; Peel, John S. (2010). "A Possible Anomalocaridid from the Cambrian Sirius Passet Lagerstätte, North Greenland". Journal of Paleontology. 84 (2): 352–355. ISSN   0022-3360.
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  28. ↑ Vannier, Jean (2009-03-01). "L'Explosion cambrienne ou l'émergence des écosystèmes modernes". Comptes Rendus Palevol. Histoire évolutive de la Vie/Evolutionary history of Life. 8 (2): 133–154. doi:10.1016/j.crpv.2008.10.006. ISSN   1631-0683.
  29. ↑ Zhang, Lei; Chang, Shan; Khan, Maliha Zareen; Feng, Qinglai; Danelian, Taniel; Clausen, Sébastien; Tribovillard, Nicolas; Steiner, Michael (2018-04-15). "The link between metazoan diversity and paleo-oxygenation in the early Cambrian: An integrated palaeontological and geochemical record from the eastern Three Gorges Region of South China". Palaeogeography, Palaeoclimatology, Palaeoecology. 495: 24–41. doi:10.1016/j.palaeo.2017.12.007. ISSN   0031-0182.
  30. 1 2 3 4 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.
  31. ↑ Yang, Chuan; Li, Xian-Hua; Zhu, Maoyan; Condon, Daniel J.; Chen, Junyuan (2018-03-15). "Geochronological constraint on the Cambrian Chengjiang biota, South China". Journal of the Geological Society. 175 (4): 659–666. Bibcode:2018JGSoc.175..659Y. doi:10.1144/jgs2017-103. ISSN   0016-7649. Archived from the original on 2025-04-07. Retrieved 2025-09-14.
  32. ↑ Yang, Chuan; Bowyer, Fred T.; Condon, Daniel J.; Li, Xian-Hua; Zhu, Maoyan (2023-04-15). "New U-Pb age from the Shuijingtuo Formation (Yangtze Gorges area) and its implications for the Cambrian timescale". Palaeogeography, Palaeoclimatology, Palaeoecology. 616 111477. Bibcode:2023PPP...61611477Y. doi:10.1016/j.palaeo.2023.111477. ISSN   0031-0182.
  33. ↑ Zhao, Bingshuang; Long, Xiaoping; Chang, Chao (2024-03-01). "Early Cambrian sedimentary rocks in South China: A link between oceanic oxygenation and biological explosion". Earth-Science Reviews. 250, 104708. doi:10.1016/j.earscirev.2024.104708. ISSN   0012-8252.
  34. ↑ Tan, Yineng; Xiao, Xianming; Gao, Ping; Meng, Guangming; Wang, Qiang; Liu, Wei; Feng, Yue (2025-06-15). "Sedimentary Environment and Organic Matter Enrichment Mechanism of the Lower Cambrian Shale in the Northern Margin of the Yangtze Platform". Journal of Marine Science and Engineering. 13 (6): 1175. Bibcode:2025JMSE...13.1175T. doi: 10.3390/jmse13061175 .
  35. 1 2 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.
  36. 1 2 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. ISSN   0022-3360.
  37. ↑ Castle Jones, Jack; M. Jackquet, Sarah; Chen, Feiyang; J. Betts, Marissa; Zhang, Zhiliang; Anthony Hall, Philip; A. Brock, Glenn; Klaebae, Robert (April 2025). "A new integrated lower Cambrian chronostratigraphy for the Normanville Group, eastern Stansbury Basin, with definition of the oldest small shelly fossil zones in South Australia" (PDF). Australasian Palaeontological Memoirs– via Researchgate.
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