Cnidarian Affinity Research Articles

Resurgence of cloudinomorph fossils with possible cnidarian affinity at the peak of the Cambrian Explosion (Cambrian Series 2, Stage 3) in southern Shaanxi, China

AbstractDuring the Precambrian–Cambrian transition, tubicolous animals were prevalent among small shelly fossils. These include the oldest‐known skeletal fossil Cloudina from the terminal Ediacaran, and anabarites and hyoliths from the early Cambrian; considered to be possible annelids, cnidarians, and molluscs, respectively. Tubular fossils have important bio‐stratigraphic significance during this period, and their diversity and evolutionary radiation trend herald the Cambrian explosion. However, the relative morphological simplicity of these fossils and lack of preserved soft‐body information has resulted in poor taxonomic constraints. Here, numerous tubular fossils exhibiting multi‐stage cylindrical or conical cups were recovered from the middle–upper Guojiaba Formation of Cambrian Series 2, Stage 3, in Mianxian, South China. One new genus (Mianxiantubus) and three new species (M. cyathiformis, M. obconicus, and M. varius) were established to accommodate the morphological diversity of the fossils. However, their affinities remain contentious and undetermined and have been tentatively ascribed to Cnidaria. The possible morphology and growth patterns of Mianxiantubus suggest a close relationship with cloudinomorph fossils, although it is notably distinct from the quintessential cloudinids owing to the presence of transverse septa. Moreover, many other tubular fossils have been recovered from the same level, which may extend to the overlying Xiannvdong Formation (Stage 3), co‐occurring with archaeocyathids. This suggests that tubicolous organisms continued to diversify and occupied specific ecological niches even during the peak phase of the Cambrian explosion, dominated by bilateral epifaunal vagrants.

Exceptional soft tissue preservation reveals a cnidarian affinity for a Cambrian phosphatic tubicolous enigma.

Exoskeletal dwelling tubes are widespread among extant animals and early fossil assemblages. Exceptional fossils from the Cambrian reveal independent origins of tube dwelling by several clades including cnidarians, lophophorates, annelids, scalidophorans, panarthropods and ambulacrarians. However, most fossil tubes lack preservation of soft parts, making it difficult to understand their affinities and evolutionary significance. Gangtoucunia aspera (Wulongqing Formation, Cambrian Stage 4) was an annulated, gradually expanding phosphatic tube, with occasional attachments of multiple, smaller juveniles and has previously been interpreted as the dwelling tube of a 'worm' (e.g. a scalidophoran), lophophorate or problematicum. Here, we report the first soft tissues from Gangtoucunia that reveal a smooth body with circumoral tentacles and a blind, spacious gut that is partitioned by septa. This is consistent with cnidarian polyps and phylogenetic analysis resolves Gangtoucunia as a total group medusozoan. The tube of Gangtoucunia is phenotypically similar to problematic annulated tubular fossils (e.g. Sphenothallus, Byronia, hyolithelminths), which have been compared to both cnidarians and annelids, and are among the oldest assemblages of skeletal fossils. The cnidarian characters of G. aspera suggest that these early tubular taxa are best interpreted as cnidarians rather than sessile bilaterians in the absence of contrary soft tissue evidence.

Transcriptomic Insights into the Diversity and Evolution of Myxozoa (Cnidaria, Endocnidozoa) Toxin-like Proteins.

Myxozoa is a speciose group of endoparasitic cnidarians that can cause severe ecological and economic effects. Their cnidarian affinity is affirmed by genetic relatedness and the presence of nematocysts, historically called “polar capsules”. Previous studies have revealed the presence of toxin-like proteins in myxozoans; however, the diversity and evolution of venom in Myxozoa are not fully understood. Here, we performed a comparative analysis using the newly sequenced transcriptomes of five Myxobolidae species as well as some public datasets. Toxin mining revealed that myxozoans have lost most of their toxin families, while most species retained Kunitz, M12B, and CRISP, which may play a role in endoparasitism. The venom composition of Endocnidozoa (Myxozoa + Polypodium) differs from that of free-living cnidarians and may be influenced by ecological and environmental factors. Phylogenetic analyses showed that toxin families of myxozoans and free-living cnidarians were clustered into different clades. Selection analyses showed that purifying selection was the dominant evolutionary pressure in toxins, while they were still influenced by episodic adaptive selection. This suggests that the potency or specificity of a particular toxin or species might increase. Overall, our findings provide a more comprehensive framework for understanding the diversity and evolution of Myxozoa venoms.

Enduring evolutionary embellishment of cloudinids in the Cambrian.

The Ediacaran–Cambrian transition and the following Cambrian Explosion are among the most fundamental events in the evolutionary history of animals. Understanding these events is enhanced when phylogenetic linkages can be established among animal fossils across this interval and their trait evolution monitored. Doing this is challenging because the fossil record of animal lineages that span this transition is sparse, preserved morphologies generally simple and lifestyles in the Ediacaran and Cambrian commonly quite different. Here, we identify derived characters linking some members of an enigmatic animal group, the cloudinids, which first appeared in the Late Ediacaran, to animals with cnidarian affinity from the Cambrian Series 2 and the Miaolingian. Accordingly, we present the first case of an animal lineage represented in the Ediacaran that endured and diversified successfully throughout the Cambrian Explosion by embellishing its overall robustness and structural complexity. Among other features, dichotomous branching, present in some early cloudinids, compares closely with a cnidarian asexual reproduction mode. Tracking this morphological change from Late Ediacaran to the Miaolingian provides a unique glimpse into how a primeval animal group responded during the Cambrian Explosion.

New probable cnidarian fossils from the lower Cambrian of the Three Gorges area, South China, and their ecological implications

Lower Cambrian assemblages of phosphatic and chitinous tubular fossils of probable cnidarian affinities were recovered from the Yanjiahe, Shuijingtuo and Shipai formations in the Three Gorges area, South China. Terreneuvian Cambrorhytium cf. C. major co-occur with an unnamed taxon in the Yanjiahe Formation. They can be compared with specimens from the Ediacaran Miaohe Fauna in the Three Gorges area. The most abundant and diversified cnidarian assemblages, including Cambrorhytium gracilis n. sp., Cambrorhytium cf. major, Cambrorhytium minor, Sphenothallus songlinensis, Sphenothallus taijiangensis?, Sphenothallus kozaki, ?Sphenothallus sp., ?Byronia sp., and ?Mackenzia sp. are reported from the overlying, Cambrian Stage 3–4, Shuijingtuo and Shipai formations. These new fossils show previously unknown evidence for cnidarian affinities, such as an attachment disk, clonal clusters and probable budding structures. These diversified assemblages of probable cnidarian fossils further fill major gaps in the Cambrian record of stem metazoans and document associated early evolutionary patterns. In addition, our discovery suggests that along with sponges, these tubular fossils represent another important component of benthic ecosystems that colonized often dysoxic, deep-settings during the Cambrian explosion. The observed increases of average body-size and biomineralization among these probable cnidarians are tentatively linked to oxygenation of deep oceanic settings and appearance of predatory pressure during the Ediacaran–Cambrian transition, respectively.

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

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 stem-group 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 total-group Cnidaria is greater than previously assumed.

The origin of tetraradial symmetry in cnidarians

Serially arranged sets of eight septa-like structures occur in the basal part of phosphatic tubes of Sphenothallus from the early Ordovician (early Floian) Fenxiang Formation in Hubei Province of China. They are similar in shape, location and number, to cusps in chitinous tubes of extant coronate scyphozoan polyps, which supports the widely accepted cnidarian affinity of this problematic fossil. However, unlike the recent Medusozoa, the tubes of Sphenothallus are flattened at later stages of development, showing biradial symmetry. Moreover, the septa (cusps) in Sphenothallus are obliquely arranged, which introduces a bilateral component to the tube symmetry. This makes Sphenothallus similar to the Early Cambrian Paiutitubulites, having similar septa but with even more apparent bilateral disposition. Biradial symmetry also characterizes the Early Cambrian tubular fossil Hexaconularia, showing a similarity to the conulariids. However, instead of being strictly tetraradial like conulariids, Hexaconularia shows hexaradial symmetry superimposed on the biradial one. A conulariid with a smooth test showing signs of the ‘origami’ plicated closure of the aperture found in the Fenxiang Formation supports the idea that tetraradial symmetry of conulariids resulted from geometrical constrains connected with this kind of closure. Its minute basal attachment surface makes it likely that the holdfasts characterizing Sphenothallus and advanced conulariids are secondary features. This concurs with the lack of any such holdfast in the earliest Cambrian Torellella, as well as in the possibly related Olivooides and Quadrapyrgites. Bilaterally arranged internal structures in polyps representing probably the oldest medusozoans support the suggestions based on developmental evidence that the ancestor of cnidarians also was a bilaterally symmetrical animal. This is one more example of fossil data that strictly fit the molecular phylogenetic evidence but not necessarily morphology-based zoological interpretations.

Skeletogenesis in problematic Late Proterozoic Lower Metazoa

This paper discusses supporting structures in problematic Late Precambrian Lower Metazoa, sponge and cnidarian affinity. These structure include aggregates of agglutinated mineral particles; spicule-like elements; mineralized spicules, long fibrous fiberlike elements; dense covers-thecae(?); monolithic and module organic and mineralized structures. In clastic deposits, mineralized remains could probably be absent, due to anoxic conditions characteristic of the Late Proterozoic shelf environment. As a hard skeleton is part of the archetype of many Phanerozoic taxa, the analysis of such structures allows discussion of the body plans and phylogeny of some elements of the Ediacaran “fauna” interpreted as lower Metazoa.

Sphenothallus (Cnidaria?) in the Late Ordovician of Baltica, its mineral composition and microstructure

Sphenothallus is a problematic fossil with possible cnidarian affinities. Two species of Sphenothallus, S. aff. longissimus and S. kukersianus, occur in the normal marine sediments of the Late Ordovician of Estonia. S. longissimus is more common than S. kukersianus and has a range from early Sandbian to middle Katian. Sphenothallus had a wide paleobiogeographic distribution in the Late Ordovician. The tubes of Sphenothallus are composed of lamellae with a homogeneous microstructure. The homogeneous microstructure could represent a diagenetic fabric, based on the similarity to diagenetic structures in Torellella (Cnidaria?, Hyolithelminthes). Tubes of Sphenothallus have an apatitic composition, but one tube contains lamellae of diagenetic calcite within the apatitic structure. Sphenothallus presumably had originally biomineralized apatitic tubes. Different lattice parameters of the apatite indicate that biomineralization systems of phosphatic cnidarians Sphenothallus and Conularia sp. may have been different.

A Diploblastic Radiate Animal at the Dawn of Cambrian Diversification with a Simple Body Plan: Distinct from Cnidaria?

BackgroundMicrofossils of the genus Punctatus include developmental stages such as blastula, gastrula, and hatchlings, and represent the most complete developmental sequence of animals available from the earliest Cambrian. Despite the extremely well-preserved specimens, the evolutionary position of Punctatus has relied only on their conical remains and they have been tentatively assigned to cnidarians. We present a new interpretation of the Punctatus body plan based on the developmental reconstruction aided by recent advances in developmental biology.Results Punctatus developed from a rather large egg, gastrulated in a mode of invagination from a coeloblastura, and then formed a mouth directly from the blastopore. Spiny benthic hatchlings were distinguishable from swimming or crawling ciliate larvae found in cnidarians and sponges. A mouth appeared at the perihatching embryonic stage and was renewed periodically during growth, and old mouths transformed into the body wall, thus elongating the body. Growing animals retained a small blind gut in a large body cavity without partitioning by septa and did not form tentacles, pedal discs or holdfasts externally. A growth center at the oral pole was sufficient for body patterning throughout life, and the body patterning did not show any bias from radial symmetry.ConclusionsContrary to proposed cnidarian affinity, the Punctatus body plan has basic differences from that of cnidarians, especially concerning a spacious body cavity separating ectoderm from endoderm. The lack of many basic cnidarian characters in the body patterning of Punctatus leads us to consider its own taxonomic group, potentially outside of Cnidaria.

Phenetic phylogenetics of tentaculitoids – extinct, problematic calcareous tube-forming organisms

Tentaculitoids have traditionally been assigned to either Mollusca or Annelida. In addition, cnidarian, brachiopod, bryozoan, phoronid and sponge affinities have been proposed. Similarity analyses carried out with tentaculitoid characters place them in a cluster together with Brachiozoa (Brachiopoda+Phoronida). Tentaculitoids are less similar to Mollusca and Bryozoa. No support was found for the annelid, cnidarian and sponge affinities. Thus, tentaculitoids belong to Lophotrochozoa with a high degree of certainty. They are best classified as “lophophorates”, most likely Brachiozoa.

Ediacaran Discs from the Jodhpur Sandstone, Marwar Supergroup, India: A Biological Diversification or Taphonomic Interplay?

The noncarbonaceous Ediacaran discs of variable morphologies from the Jodhpur Sandstone Formation of the Marwar Supergroup, western Rajasthan, suggest different biologic affinities of plant and animal kingdom. These discs are commonly preserved on the bedding surfaces of siliciclastic sandstone and shale in strong positive relief and appear to possess a flexible to rigid body. Discs assignable to Aspidella, Cyclomedusa, Nimbia and Heimalora; all possibly inclining towards cnidarian affinity are being reported from the sandstone beds in Sursagar area. Variable morphologies among discs preserved in siliciclastic shale beds from the Artiya Kalan area support scyphozoan affinity (earlier named Marsonia from the same locality) and cnidarian affinity for small discs comparable with Funisia (considered being the first animals having sexual reproduction). Disc’s morphologies also suggest ephyra stage of Aurilia (a cnidarian form) or budding stages of some fungi, like Germinosphaera (multicellular benthic fungal fossils) and noncarbonaceous discs with well preserved wrinkles and folds like in Chuaria. Discs from the Jodhpur Sandstone, may at times display taphonomic interplay, but consistency and repetition in morphology support variable biological affinities representing diverse assemblage and advance ecosystem prevailing during Ediacaran period. A degree of genetic variability can be expected within any taxa, and this may be compounded by preservation factors affecting the Jodhpur Ediacaran discs. Sudden increase in size or gigantism is a common feature of Ediacaran life, which is evident in case of Jodhpur discs also. On the basis of fossil assemblage, the Jodhpur Group (the Marwar Supergroup) is regionally correlated with the Bhander Group of the Vindhyan Supergroup and Krol Group of Lesser Himalaya. Globally, the assemblage is comparable with the Long Mynd Group, Shropshire, UK, Fermuse Formation Newfoundland, South Australia, Russia and Norway.

The Aperture and Its Closure in an Ordovician Conulariid

The conulariids, an enigmatic fossil group believed to be of cnidarian (scyphozoan) affinity, have four−sided, acutely pyramidal exoskeletons terminated in apertural closures. To date, three main closure types have been recognised in conulariids (plicated, triangular lappets, and lobate lappets) but the first type is poorly illustrated in the literature. Here we present the first photographic illustration of an unequiv− ocal plicated closure in Metaconularia? anomala, based on study of the rich (1700+ specimens) material from the Upper Ordovician of the Prague Basin. This closure is formed by inwardly folded, triangular lappets centred on each of the four faces, with kite−shaped elements centred on the four corners forming a webbing between the lappets. Plicated closures were evidently rare in conulariids and restricted to a few Ordovician species.

Haeckelia (= Euchlora) and Hydroctena and the phylogenetic interrelationships of Cnidaria and Ctenophora

A scrutiny of the literature shows that the ctenophore Haeckelia (= Euchlora) ruba has only kleptocnidae and that Hydroctena salenskii is a ctenophore without special cnidarian affinities. The “missing links” between cnidarians and ctenophores have thus turned out to be based on misinterpretations and must be excluded from future discussions on phylogeny.

SYSTEMATIC DESCRIPTION AND PHYLOGENETIC AFFINITY OF TUBULAR MICROFOSSILS FROM THE EDIACARAN DOUSHANTUO FORMATION AT WENG’AN, SOUTH CHINA

Abstract: This paper provides a systematic treatment of tubular microfossils collected from dolomitic phosphorites of the Ediacaran Doushantuo Formation at Weng’an, South China. These microfossils were investigated using petrographic, acid extraction and re‐embedding techniques. Four morphological genera and five morphospecies are described: Ramitubus increscens gen. et sp. nov., Ramitubus decrescens gen. et sp. nov., Sinocyclocyclicus guizhouensis, Quadratitubus orbigoniatus, and Crassitubus costatus gen. et sp. nov. They are characterized by cylindrical (R. increscens, R. decrescens, S. guizhouensis and C. costatus) or tetragonal (Q. orbigoniatus) tubes with closely spaced cross‐walls. Ramitubus has mostly complete cross‐walls, whereas all other taxa have regularly intercalated complete and incomplete cross‐walls. Some of them branch dichotomously (R. increscens and R. decrescens), others have a longitudinal ridge running along a curved tube (C. costatus).The palaeoecology, ontogeny, and phylogenetic affinity of these microfossils are still uncertain. They probably represent non‐biomineralizing organisms in the Ediacaran ocean. Ramitubus (and possibly all other morphotaxa described in this paper) was probably benthic and grew unidirectionally and episodically. The incomplete cross‐walls could have been formed through terminal addition or, alternatively, through intercalary insertion. It is possible that some or all morphotaxa described may represent ontogenetic or ecophenotypic variations of one or a few closely related biological species. If so, then the combination of morphological features (complete and incomplete cross‐walls, tetraradial symmetry, and longitudinal ridge) can negate a cyanobacterial or algal interpretation, and point to a tentative cnidarian affinity.

Precambrian phosphatized embryos and larvae from the Doushantuo Formation and their affinities, Guizhou (SW China)

Weng’an phosphates of the Precambrian Doushantuo Formation, Guizhou (southwestern China) preserve a large number of exquisite biological structures, which are mostly micro-spherical and represent seaweeds, acritarchs and developing eggs related to various groups of metazoans. Here is a report of a variety of developing eggs and larvae, which are most probably of Cnidarian affinity. The eggs examined in the study are composed of early cleavage embryos and two-layered gastrulae. The early cleavage embryos are radial and total cleavage with equal-size blastomeres. The gastrulae mostly bear a large archenteron, which is filled with yolk-degrading organic matter. Ovoid to fusiform planula-like larvae identified in thin sections under light microscope are mostly mouthless and their gastrovascular cavity is filled with possible yolk-degrading organic matter. They are likely representatives of non-feeding larva. The uncommon planula-like structures are hollow, with each having a mouth-like structure on its narrow end. We interpret them as feeding larva. Study of these embryos with possible Cnidarian affinities shed new insight on the origin of metazoans.

Biodiversity and Evolution of the Myxozoa

Myxozoans (phylum Myxozoa) are metazoan parasites utilizing invertebrate and (mainly) aquatic vertebrate hosts. They have in common with cnidarians the possession of virtually identical, highly complex organelles, namely the polar capsules in myxozoan spores, serving for attachment to new hosts and the nematocysts in surface epithelia of cnidarians, serving for food capture. Although myxozoan spores are multicellular, the simple trophic body forms of almost all species, reduced to syncytial plasmodia or single cells, reveal no clues to myxozoan ancestry or phylogenetic relationships. The myxozoan genus Buddenbrockia is one of only two known genera belonging to a clade which diverged early in the evolution of the Myxozoa. Today the Myxozoa are represented by two classes, the Myxosporea, containing all the better-known genera, which alternate between fish and annelids, and the Malacosporea, containing Buddenbrockia and Tetracapsuloides, parasitising bryozoans. The latter genus also infects salmonid fish, causing proliferative kidney disease (PKD). The enigmatic Buddenbrockia has retained some of its ancestral features in a body wall of two cell layers and a worm-like shape, maintained by four longitudinally-running muscle blocks, similar to a gutless nematode and suggestive of a bilaterian ancestry. Although some analyses of 18S rDNA sequences tend towards a cnidarian (diploblast) affinity for myxozoans, the majority of these studies place them within, or sister to, the Bilateria. The latter view is supported by their possession of central class Hox genes, so far considered to be synapomorphic for Bilateria. The simple body form is, therefore, an extreme example of simplification due to parasitism. Various hypotheses for the occurrence of identical complex organelles (nematocysts and polar capsules) in diploblast and triploblast phyla are evaluated: common ancestry, convergent evolution, gene transfer and, especially, endosymbiosis. A theory of the evolution of their digenetic life cycles is proposed, with the invertebrate as primary host and secondary acquisition of the vertebrate host serving for asexual population increase.

Precambrian Animal Life: Probable Developmental and Adult Cnidarian Forms from Southwest China

The evolutionary divergence of cnidarian and bilaterian lineages from their remote metazoan ancestor occurred at an unknown depth in time before the Cambrian, since crown group representatives of each are found in Lower Cambrian fossil assemblages. We report here a variety of putative embryonic, larval, and adult microfossils deriving from Precambrian phosphorite deposits of Southwest China, which may predate the Cambrian radiation by 25–45 million years. These are most probably of cnidarian affinity. Large numbers of fossilized early planula-like larvae were observed under the microscope in sections. Though several forms are represented, the majority display remarkable conformity, which is inconsistent with the alternative that they are artifactual mineral inclusions. Some of these fossils are preserved in such high resolution that individual cells can be discerned. We confirm in detail an earlier report of the presence in the same deposits of tabulates, an extinct crown group anthozoan form. Other sections reveal structures that most closely resemble sections of basal modern corals. A large number of fossils similar to modern hydrozoan gastrulae were also observed. These again displayed great morphological consistency. Though only a single example is available, a microscopic animal remarkably similar to a modern adult hydrozoan is also presented. Taken together, the new observations reported in this paper indicate the existence of a diverse and already differentiated cnidarian fauna, long before the Cambrian evolutionary event. It follows that at least stem group bilaterians must also have been present at this time.

An unusual micromorphic brachiopod from the Middle Cambrian of north-eastern New South Wales, Australia

Anomalocalyx cawoodi new genus and new species, from Middle Cambrian (Floran-Undillan) allochthonous limestone clasts of the Murrawong Creek Formation, north eastern New South Wales, is characterised by a deep, tapering, conical ventral valve with a pair of simple teeth, an arched pseudodeltidium, well defined radial costae, crossed at more or less regular intervals by continuous concentric growth lamellae, and a presumed calcium carbonate shell composition, all suggesting an affinity with the Brachiopoda. Anomalocalyx cawoodi also possesses a number of unusual morphological features including an elongate, tapering interior tube extending along the inner posterior margin of the ventral valve, under the pseudodeltidium, that may be interpreted as a spondylium. Though possible cnidarian and molluscan affinities are fully explored, the weight of available evidence suggests the affinities of A. cawoodi are with the Brachiopoda.

The Late Precambrian fossil Kimberella is a mollusc-like bilaterian organism

The fossil Kimberella quadrata was originally described from late Precambrian rocks of southern Australia1. Reconstructed as a jellyfish2, it was later assigned to the cubozoans (‘box jellies’), and has been cited as a clear instance of an extant animal lineage present before the Cambrian3,4,5,6,7. Until recently, Kimberella was known only from Australia, with the exception of some questionable north Indian specimens8. We now have over thirty-five specimens of this fossil from the Winter Coast of the White Sea in northern Russia. Our study of the new material does not support a cnidarian affinity. We reconstruct Kimberella as a bilaterally symmetrical, benthic animal with a non-mineralized, univalved shell, resembling a mollusc in many respects. This is important evidence for the existence of large triploblastic metazoans in the Precambrian and indicates that the origin of the higher groups of protostomes lies well back in the Precambrian.