Tiny Sea Anemone from the Lower Cambrian of China

Han, Jian; Kubota, Shin; Uchida, Hiro'omi; Stanley, George D.; Yao, Xingyu; Shu, Degan; Li, Yong; Yasui, Kohichiroh

doi:10.1371/journal.pone.0013276

Cited by 55 publications

(52 citation statements)

References 46 publications

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“…sinica Represents a Stem-Group Cnidarian. X. sinica has been alternatively interpreted as a crown-group cnidarian (16,(19)(20)(21)(22), a ctenophore (23,26), a lophophorate (27), or a survivor of vendobionts (28). We have shown here that X. sinica had a relatively simple anatomy with a radial symmetry, a polypoid body, and a blind gut containing septum-like structures.…”

Section: Significancementioning

confidence: 75%

“…These putative species have been assigned to three different animal groups: hexacorals (16,(19)(20)(21)(22)(23)(24), octocorals (17,25), and hemichordates (18), respectively. However, alternative views suggest that X. sinica was a ctenophore (23, 26), a lophophorate (27), an Ediacaran survivor (28), or a metazoan of unknown affinity (29,30). Moreover, the phylogenetic placement of C. wangii as an ancient sea pen remains ambiguous (31) and the assignment of G. abilus to hemichordates has also been questioned (32).…”

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confidence: 99%

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Three Cambrian fossils assembled into an extinct body plan of cnidarian affinity

Han

Zhang

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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The early Cambrian problematica Xianguangia sinica, Chengjiangopenna wangii, and Galeaplumosus abilus from the Chengjiang biota (Yunnan, China) have caused much controversy in the past and their phylogenetic placements remain unresolved. Here we show, based on exceptionally preserved material (85 new specimens plus type material), that specimens previously assigned to these three species are in fact parts of the same organism and propose that C. wangii and G. abilus are junior synonyms of X. sinica. Our reconstruction of the complete animal reveals an extinct body plan that combines the characteristics of the three described species and is distinct from all known fossil and living taxa. This animal resembled a cnidarian polyp in overall morphology and having a gastric cavity partitioned by septum-like structures. However, it possessed an additional body cavity within its holdfast, an anchoring pit on the basal disk, and feather-like tentacles with densely ciliated pinnules arranged in an alternating pattern, indicating that it was a suspension feeder rather than a predatory actiniarian. Phylogenetic analyses using Bayesian inference and maximum parsimony suggest that X. sinica is a stemgroup cnidarian. This relationship implies that the last common ancestor of X. sinica and crown cnidarians was probably a benthic, polypoid animal with a partitioned gastric cavity and a single mouth/anus opening. This extinct body plan suggests that feeding strategies of stem cnidarians may have been drastically different from that of their crown relatives, which are almost exclusively predators, and reveals that the morphological disparity of totalgroup Cnidaria is greater than previously assumed.Xianguangia sinica | Chengjiangopenna wangii | Galeaplumosus abilus | ciliary suspension feeder | cnidarian stem group

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Section: Significancementioning

confidence: 75%

mentioning

confidence: 99%

Three Cambrian fossils assembled into an extinct body plan of cnidarian affinity

Han

Zhang

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…Also, bioturbation may have been conducive to the establishment of microbes, meiofauna and tiny animals within the burrows57172. There is increased evidence that tiny animals7374 and meiofauna757677 have been important components of Cambrian marine ecosystems. On the contrary, sediment remobilization by these deposit feeders may have been detrimental for colonization of sessile suspension feeders, a phenomenon referred to as trophic group amensalism478.…”

Section: Discussionmentioning

confidence: 99%

The impact of deep-tier burrow systems in sediment mixing and ecosystem engineering in early Cambrian carbonate settings

Zhang¹,

Yong-an²,

Buatois

et al. 2017

Sci Rep

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Bioturbation plays a substantial role in sediment oxygen concentration, chemical cycling, regeneration of nutrients, microbial activity, and the rate of organic matter decomposition in modern oceans. In addition, bioturbators are ecosystem engineers which promote the presence of some organisms, while precluding others. However, the impact of bioturbation in deep time remains controversial and limited sediment mixing has been indicated for early Paleozoic seas. Our understanding of the actual impact of bioturbation early in the Phanerozoic has been hampered by the lack of detailed analysis of the functional significance of specific burrow architectures. Integration of ichnologic and sedimentologic evidence from North China shows that deep-tier Thalassinoides mazes occur in lower Cambrian nearshore carbonate sediments, leading to intense disruption of the primary fabric. Comparison with modern studies suggest that some of the effects of this style of Cambrian bioturbation may have included promotion of nitrogen and ammonium fluxes across the sediment-water interface, average deepening of the redox discontinuity surface, expansion of aerobic bacteria, and increase in the rate of organic matter decomposition and the regeneration of nutrients. Our study suggests that early Cambrian sediment mixing in carbonate settings may have been more significant than assumed in previous models.

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“…These fossils include a kind of scyphopolyp with many filiform tentacles [9], some sea anemone-like cnidarians [10], as well as many pentamerous embryos [11], [12]. The latter, referred to as co-occurring Punctatus emeiensis and Olivooides multisulcatus , have been intimated as having a problematic affinity with coronate scyphozoans [11], [12].…”

Section: Introductionmentioning

confidence: 99%

Early Cambrian Pentamerous Cubozoan Embryos from South China

et al. 2013

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BackgroundExtant cubozoans are voracious predators characterized by their square shape, four evenly spaced outstretched tentacles and well-developed eyes. A few cubozoan fossils are known from the Middle Cambrian Marjum Formation of Utah and the well-known Carboniferous Mazon Creek Formation of Illinois. Undisputed cubozoan fossils were previously unknown from the early Cambrian; by that time probably all representatives of the living marine phyla, especially those of basal animals, should have evolved.MethodsMicroscopic fossils were recovered from a phosphatic limestone in the Lower Cambrian Kuanchuanpu Formation of South China using traditional acetic-acid maceration. Seven of the pre-hatched pentamerous cubozoan embryos, each of which bears five pairs of subumbrellar tentacle buds, were analyzed in detail through computed microtomography (Micro-CT) and scanning electron microscopy (SEM) without coating.ResultsThe figured microscopic fossils are unequivocal pre-hatching embryos based on their spherical fertilization envelope and the enclosed soft-tissue that has preserved key anatomical features arranged in perfect pentaradial symmetry, allowing detailed comparison with modern cnidarians, especially medusozoans. A combination of features, such as the claustrum, gonad-lamella, suspensorium and velarium suspended by the frenula, occur exclusively in the gastrovascular system of extant cubozoans, indicating a cubozoan affinity for these fossils. Additionally, the interior anatomy of these embryonic cubozoan fossils unprecedentedly exhibits the development of many new septum-derived lamellae and well-partitioned gastric pockets unknown in living cubozoans, implying that ancestral cubozoans had already evolved highly specialized structures displaying unexpected complexity at the dawn of the Cambrian. The well-developed endodermic lamellae and gastric pockets developed in the late embryonic stages of these cubozoan fossils are comparable with extant pelagic juvenile cubomedusae rather than sessile cubopolyps, whcih indicates a direct development in these fossil taxa, lacking characteristic stages of a typical cnidarian metagenesis such as planktonic planula and sessile polyps.

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Tiny Sea Anemone from the Lower Cambrian of China

Cited by 55 publications

References 46 publications

Three Cambrian fossils assembled into an extinct body plan of cnidarian affinity

Three Cambrian fossils assembled into an extinct body plan of cnidarian affinity

The impact of deep-tier burrow systems in sediment mixing and ecosystem engineering in early Cambrian carbonate settings

Early Cambrian Pentamerous Cubozoan Embryos from South China

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