Evidence of clonal budding in a radial cluster of Paraconularia crustula (White) (Pennsylvanian: ?Cnidaria)

Monospecific conulariid clusters have been interpreted as products of gregarious behavior or as clonal colonies, with members of a colony originally inclined at a high angle to the substrate and connected to each other at their apices. However. individuals in all previously documented clusters are preserved parallel, or nearly parallel, to bedding, and their apices are not preserved. We describe a cluster of three Paraconularia crustula (White) (Pennsylvanian of Missouri, USA) in which the individual specimens exhibit an original steeply inclined orientation. The individuals in this cluster converge adapically on an extremely thin. crumpled sheet of apatitic material that is similar to conulariid test material. The conulariids and associated sheet bear a striking resemblance to regenerated, clonal colonies of polypoid coronatid scyphozoans. Such colonies arise from a thin, periderm-covered sheet of non-differentiated soft tissue, produced following severance of a single parent polyp. We suggest that the conulariid cluster originated through a similar process. Should this interpretation be corroborated by the discovery of better preserved conulariid clusters, it would provide strong additional evidence for the hypothesis of a scyphoroan affinity for conulariids     

Mesodermal anatomies in cnidarian polyps and medusae

The cellular and developmental analysis of evolutionary-conserved genes directing bilaterian mesodermal and myogenic cell fate previously identified the hydromedusan entocodon and its differentiation product, the striated muscle, as mesodermal derivatives. In view of these findings we presented a hypothesis disputing the diploblast classification of cnidarians without providing further explanations for the apparent diploblasty of the polyp stage and the formation of the subepidermal striated muscle in those Medusozoa lacking the entocodon nodule (Seipel and Schmid, 2005). Hence we carried out a systematic review of the histological and experimental evidence for mesodermal differentiations in cnidarians. In anthozoan and scyphozoan but not in hydrozoan polyps the presumptive mesodermal elements include amoeboid cells, the mesentery retractor muscles and scleroblasts, all of which are embedded or deeply rooted in the extracellular matrix (mesoglea) and derive from the ectoblastemal cells invading the extracellular matrix from the gastrulation site during or shortly after endoderm formation. These data lend further support to the cnidarian mesodermate hypothesis, whereby cnidarians and bilaterians share a common triploblast ancestor, the Urtriploblast, a small, motile, possibly medusa-like organism that did not feature a sessile polyp stage in its life cycle. As a consequence the diploblasty of the hydrozoan polyps may represent a derived morphology resulting from heterochronic modulations of the gastrulation process after endoderm formation.     

Enigmatic Fossils from the Lower Carboniferous Shrimp Bed,Granton, Scotland

The Lower Carboniferous (Visean) Granton Lagerstätte (Edinburgh, Scotland) is principally known for the discovery of the conodont animal, but has also yielded numerous crustaceans and other faunas. Here we report on small branching colonies, reaching 10 mm in length. They are small, erect, arborescent, and irregularly branched with predominant monopodial and dichotomous growth. They bud in a single plane. In one specimen the wall microstructure is well preserved and it is composed of evenly spaced, linear fibers, running parallel to the axis of the stems, and connected by transverse bars. We discuss possible biological affinities of these organisms; we consider algal, poriferan, hydrozoan and bryozoan affinities. The general pattern of branching, presence of fan-like structures (interpreted here as possible gonophores) and microstructure suggests affinity to Hydrozoa, affinity to non-calcifying algae is less likely. Assuming hydrozoan nature; the microstructure might suggest affinities with the extant family Solanderiidae Marshall, 1892 that possess an internal chitinous skeleton. The EDS analysis shows that fossils discussed here are preserved as phosphates. The skeletons were probably not mineralized, the presence of phosphorus suggests that the colonies were originally composed of chitin. We describe these organisms as Caledonicratis caridum gen. et sp. nov. (Solanderiidae?, Capitata?). Colonies of C. caridum gen et. sp. nov. sometimes encrust the exuviae of crustaceans, which very probably lived in fresh to brackish water thus indicating a likely habitat of Caledonicratis.     

Conical Thecae of Precambrian Macroorganisms

On the basis of new extensive collections, made by the present authors, a group of unsegmented three-dimensional fossil remains from the Late Precambrian of Namibia and the southeastern White Sea area, including such genera as Protechiurus, Vendoglossa, and Vendoconularia, were restudied. It is established that the fossils belong to two morphologically close genera (Protechiurus and Vendoconularia), composing the new family Protechiuridae. It is possible that they represent the same genus or even species, but the incompleteness of the preservation of the Namibian member of the group prevents their integration. The fossils initially represented conical hollow elastic objects, hexagonal in the cross-section, which were open at the wide end and closed at the pointed end. The sculpture of their surface consisted of longitudinal ridges, both single and double, bounding the rows of the short transverse ridges, scalloped along one margin. Vendoconularia had wide plates which were attached to the cone outwardly along the longitudinal unpaired ridges. In general morphology and several details the fossils resemble the thecae of conulariids and anabaritids, known from Late Precambrian and Paleozoic and classified as the scyphozoan cnidarians. The main difference lays in the theca mineralization, which consists of phosphate in conulariids, carbonate in anabaritids, and is absent in the case of protechiurids. It is proposed that the protechiurids, which appeared in the fossil record first, may belong to the basal group of ancient scyphozoans, ancestral to the conulariids on the one hand, and to the anabaritids on the other.     

Convergent origins and rapid evolution of spliced leader trans-splicing in Metazoa: Insights from the Ctenophora and Hydrozoa

Replacement of mRNA 5′ UTR sequences by short sequences trans-spliced from specialized, noncoding, spliced leader (SL) RNAs is an enigmatic phenomenon, occurring in a set of distantly related animal groups including urochordates, nematodes, flatworms, and hydra, as well as in Euglenozoa and dinoflagellates. Whether SL trans-splicing has a common evolutionary origin and biological function among different organisms remains unclear. We have undertaken a systematic identification of SL exons in cDNA sequence data sets from non-bilaterian metazoan species and their closest unicellular relatives. SL exons were identified in ctenophores and in hydrozoan cnidarians, but not in other cnidarians, placozoans, or sponges, or in animal unicellular relatives. Mapping of SL absence/presence obtained from this and previous studies onto current phylogenetic trees favors an evolutionary scenario involving multiple origins for SLs during eumetazoan evolution rather than loss from a common ancestor. In both ctenophore and hydrozoan species, multiple SL sequences were identified, showing high sequence diversity. Detailed analysis of a large data set generated for the hydrozoan Clytia hemisphaerica revealed trans-splicing of given mRNAs by multiple alternative SLs. No evidence was found for a common identity of trans-spliced mRNAs between different hydrozoans. One feature found specifically to characterize SL-spliced mRNAs in hydrozoans, however, was a marked adenosine enrichment immediately 3′ of the SL acceptor splice site. Our findings of high sequence divergence and apparently indiscriminate use of SLs in hydrozoans, along with recent findings in other taxa, indicate that SL genes have evolved rapidly in parallel in diverse animal groups, with constraint on SL exon sequence evolution being apparently rare.     

Conflicting phylogenetic signals at the base of the metazoan tree

A phylogenetic framework is essential for under-standing the origin and evolution of metazoan development. Despite a number of recent molecular studies and a rich fossil record of sponges and cnidarians, the evolutionary relationships of the early branching metazoan groups to each other and to a putative outgroup, the choanoflagellates, remain uncertain. This situation may be the result of the limited amount of phylogenetic information found in single genes and the small number of relevant taxa surveyed. To alleviate the effect of these analytical factors in the phylogenetic recons-truction of early branching metazoan lineages, we cloned multiple protein-coding genes from two choanoflagellates and diverse sponges, cnidarians, and a ctenophore. Comparisons of sequences for alpha-tubulin, beta-tubulin, elongation factor 2, HSP90, and HSP70 robustly support the hypothesis that choanoflagellates are closely affiliated with animals. However, analyses of single and concatenated amino acid sequences fail to resolve the relationships either between early branching metazoan groups or between Metazoa and choano-flagellates. We demonstrate that variable rates of evolution among lineages, sensitivity of the analyses to taxon selection, and conflicts in the phylogenetic signal contained in different amino acid sequences obscure the phylogenetic associations among the early branching Metazoa. These factors raise concerns about the ability to resolve the phylogenetic history of animals with molecular sequences. A consensus view of animal evolution may require investigations of genome-scale characters.     

Shared antigenicity between the polar filaments of myxosporeans and other Cnidaria

Nematocysts containing coiled polar filaments are a distinguishing feature of members of the phylum Cnidaria. As a first step to characterizing the molecular structure of polar filaments, a polyclonal antiserum was raised in rabbits against a cyanogen bromide-resistant protein extract of mature cysts containing spores of Myxobolus pendula. The antiserum reacted only with proteins associated with extruded polar filaments. Western blot and whole-mount immunohistochemical analyses indicated a conservation of polar filament epitopes between M. pendula and 2 related cnidarians, i.e., the anthozoan, Nematostella vectensis, and the hydrozoan, Hydra vulgaris. This conservation of polar filament epitopes lends further support to a shared affinity between Myxozoa and cnidarians.     

FMRFamide immunoreactivity is generally occurring in the nervous systems of coelenterates

Abundant FMRFamide immunoreactivity has been found in the nervous systems of all hydrozoan, anthozoan, scyphozoan and ctenophoran species that were looked upon. This general and abundant occurrence shows that FMRFamide-like material must play a crucial role in the functioning of primitive nervous systems.     

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.     

Phospholipase A2 in cnidaria

Phospholipase A2 (PLA2) is an enzyme present in snake and other venoms and body fluids. We measured PLA2 catalytic activity in tissue homogenates of 22 species representing the classes Anthozoa, Hydrozoa, Scyphozoa and Cubozoa of the phylum Cnidaria. High PLA2 levels were found in the hydrozoan fire coral Millepora sp. (median 735 U/g protein) and the stony coral Pocillopora damicornis (693 U/g) that cause skin irritation upon contact. High levels of PLA2 activity were also found in the acontia of the sea anemone Adamsia carciniopados (293 U/g). Acontia are long threads containing nematocysts and are used in defense and aggression by the animal. Tentacles of scyphozoan and cubozoan species had high PLA2 activity levels: those of the multitentacled box jellyfish Chironex fleckeri contained 184 U/g PLA2 activity. The functions of cnidarian PLA2 may include roles in the capture and digestion of prey and defense of the animal. The current observations support the idea that cnidarian PLA2 may participate in the sting site irritation and systemic envenomation syndrome resulting from contact with cnidarians.     

Evolution of erect helical colony form in the Bryozoa: phylogenetic, functional, and ecological factors

Erect helical colony forms have evolved at least six separate times within the Bryozoa, but only among those in which branches are composed of a single layer of feeding zooids. The four best known genera with helical colony forms evolved independently, and each occupied different benthic marine environments, achieved different growth habits, and utilized different aspects of an array of functional potentials resulting from the radially symmetrical colonies. Examination of the distribution of these four genera ( Archimedes , Bugula , Crisidmonea , and Retiflustra ) within a theoretical morphospace of hypothetical helical colony form reveals that each occupies its own characteristic region of morphospace, broadly overlapping in some dimensions but separated in others. The genera differ markedly in the branching densities within their filtration-sheet whorls, reflecting their phylogenetic legacies rather than constructional or functional constraints associated with helical growth. In contrast, all tend toward helices in which the radiating whorls of the unilaminate branches are held at an average of 50–60° to the central axis of the colony, and this may reflect a common functional optimum associated with the cilia-driven, auto-generated currents within the helix. The region of morphospace characterized by high values of surface area – i.e. helical geometries with branches orientated at very low angles to the central axis, and with very closely spaced whorls along the axis – is entirely empty of bryozoans, and these geometries apparently represent functionally unrealistic colony forms.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 235–260.     

Dead-end evolution of the Cnidaria as deduced from 5S ribosomal RNA sequences

Using nucleotide sequences of 5S ribosomal RNAs from 2 hydrozoan jellyfishes, 3 scyphozoan jellyfishes and 2 sea anemones, a phylogenetic tree of Cnidaria has been constructed to elucidate the evolutionary relationships of radial and bilateral symmetries. The 3 classes of Cnidaria examined herein belong to one branch, which does not include other metazoan phyla such as the Platyhelminthes. The Hydrozoa (having radial symmetry without septa) and the Scyphozoa (having radial symmetry with septa) are more closely related to each other than to the Anthozoa (having bilateral symmetry with septa). In classical taxonomy, multicellular animals are considered to have evolved through organisms with radial symmetry (e.g., Cnidaria) to bilateral symmetry. Our results, however, indicate that the emergence of the Bilateria was earlier than that of the Radiata, suggesting (in opposition to Haeckel's view) that the radial symmetry of Cnidaria is an evolutionary dead end.     

Genotyping the clonal structure of a gorgonian coral, Junceella juncea (Anthozoa: Octocorallia), using microsatellite loci

The identification of different clones is fundamental to the study of population structure among organisms with mixed reproductive modes such as cnidarians. However, due to the low genetic variation of coral mtDNA and contamination by zooxanthellate DNA, very few molecular markers are available for studying the clonal structure of cnidarians. Herein we used four polymorphic loci of microsatellite DNA isolated from a zooxanthellae-free octocoral, Junceella juncea, to study its clonal structure in seven populations collected from three localities in Taiwan. In total, 40 multilocus genotypes were found among 152 colonies, and the number of genotypes (clones) identified in the seven populations ranged from 2 to 16. Each of the 40 multilocus genotypes was restricted to a single population, even where adjacent populations were only 100 m distant. The ratio of observed to expected genotypic diversity (G_o:G_e) ranged from 0.217 to 0.650, and G_o showed a significant departure from G_e (p<0.05) at each site indicating that asexual fragmentation may play a major role in the maintenance of established populations. Mean relatedness (R) values showed that genotypes within reefs were more closely related than those between regions. The results indicate that microsatellites are useful for discerning the clonal structures among and within populations at different spatial scales. Electronic supplement: Unique multilocus genotypes (clones) revealed by 4 polymorphic loci for Junceella juncea colonies collected from Xiashuijui (Reefs A, B, C, Transplant, Transect), Nanwan and Shicheng     

Phylogeny of Capitata and Corynidae (Cnidaria, Hydrozoa) in light of mitochondrial 16S rDNA data

New sequences of the partial rDNA gene coding for the mitochondrial large ribosomal subunit, 16S, are derived from 47 diverse hydrozoan species and used to investigate phylogenetic relationships among families of the group Capitata and among species of the capitate family Corynidae. Our analyses identify a well-supported clade, herein named Aplanulata, of capitate hydrozoans that are united by the synapomorphy of undergoing direct development without the ciliated planula stage that is typical of cnidarians. Aplanulata includes the important model organisms of the group Hydridae, as well as species of Candelabridae, Corymorphidae, and Tubulariidae. The hypothesis that Hydridae is closely related to brackish water species of Moerisiidae is strongly controverted by 16S rDNA data, as has been shown for nuclear 18S rDNA data. The consistent phylogenetic signal derived from 16S and 18S data suggest that both markers would be useful for broad-scale multimarker analyses of hydrozoan relationships. Corynidae is revealed as paraphyletic with respect to Polyorchidae, a group for which information about the hydroid stage is lacking. Bicorona , which has been classified both within and outside of Corynidae, is shown to have a close relationship with all but one sampled species of Coryne . The corynid genera Coryne , Dipurena , and Sarsia are not revealed as monophyletic, further calling into question the morphological criteria used to classify them. The attached gonophores of the corynid species Sarsia lovenii are confirmed as being derived from an ancestral state of liberated medusae. Our results indicate that the 16S rDNA marker could be useful for a DNA-based identification system for Cnidaria, for which it has been shown that the commonly used cytochrome c oxidase subunit 1 gene does not work.     

Back in time: a new systematic proposal for the Bilateria

Conventional wisdom suggests that bilateral organisms arose from ancestors that were radially, rather than bilaterally, symmetrical and, therefore, had a single body axis and no mesoderm. The two main hypotheses on how this transformation took place consider either a simple organism akin to the planula larva of extant cnidarians or the acoel Platyhelminthes (planuloid-acoeloid theory), or a rather complex organism bearing several or most features of advanced coelomate bilaterians (archicoelomate theory). We report phylogenetic analyses of bilaterian metazoans using quantitative (ribosomal, nuclear and expressed sequence tag sequences) and qualitative (HOX cluster genes and microRNA sets) markers. The phylogenetic trees obtained corroborate the position of acoel and nemertodermatid flatworms as the earliest branching extant members of the Bilateria. Moreover, some acoelomate and pseudocoelomate clades appear as early branching lophotrochozoans and deuterostomes. These results strengthen the view that stem bilaterians were small, acoelomate/pseudocoelomate, benthic organisms derived from planuloid-like organisms. Because morphological and recent gene expression data suggest that cnidarians are actually bilateral, the origin of the last common bilaterian ancestor has to be put back in time earlier than the cnidarian-bilaterian split in the form of a planuloid animal. A new systematic scheme for the Bilateria that includes the Cnidaria is suggested and its main implications discussed.     

Cladistic analysis of Medusozoa and cnidarian evolution

Abstract. A cladistic analysis of 87 morphological and life history characters of medusozoan cnidarians, rooted with Anthozoa, results in the phylogenetic hypothesis (Anthozoa (Hydrozoa (Scyphozoa (Staurozoa, Cubozoa)))). Staurozoa is a new class of Cnidaria consisting of Stauromedusae and the fossil group Conulatae. Scyphozoa is redefined as including those medusozoans characterized by strobilation and ephyrae (Coronatae, Semaeostomeae, and Rhizostomeae). Within Hydrozoa, Limnomedusae is identified as either the earliest diverging hydrozoan lineage or as the basal group of either Trachylina (Actinulida (Trachymedusae (Narcomedusae, Laingiomedusae))) or Hydroidolina (Leptothecata (Siphonophorae, Anthoathecata)). Cladistic results are highly congruent with recently published phylogenetic analyses based on 18S molecular characters. We propose a phylogenetic classification of Medusozoa that is consistent with phylogenetic hypotheses based on our cladistic results, as well as those derived from 18S analyses. Optimization of the characters presented in this analysis are used to discuss evolutionary scenarios. The ancestral cnidarian probably had a sessile biradial polyp as an adult form. The medusa is inferred to be a synapomorphy of Medusozoa. However, the ancestral process (metamorphosis of the apical region of the polyp or lateral budding involving an entocodon) could not be inferred unequivocally. Similarly, character states for sense organs and nervous systems could not be inferred for the ancestral medusoid of Medusozoa.     

Studies on four new species of the malacocarpic Sargassum (Sargassaceae, Heterokontophyta) in China

In this paper, four new species of malacocarpic Sargassum are described: S. fuliginosoidesTseng et Lu sp. nov. is characterized by its discoid holdfast, the presence of the bulbs on the basal parts of the primary branches and very thick, lanceolate leaves. S. gemmiphorum Tseng et Lu sp. nov. is characterized by its conical holdfast, usually branched axis and very long, narrow, thin, denticulate leaves. S. shandongense Tseng, Zhang et Lu sp. nov. is characterized by its discoid holdfast, flattened primary branches, its leaves mostly entire or wavy at the margins and its racemose to paniculate receptacles. S. qingdaoense Tseng et Lu sp. nov. is characterized by the presence of the glandular dots on the ultimate branches and elongated lanceolate, acute, mostly wavy leaves.     

A novel reef coral symbiosis

Reef building corals form close associations with unicellular microalgae, fungi, bacteria and archaea, some of which are symbiotic and which together form the coral holobiont. Associations with multicellular eukaryotes such as polychaete worms, bivalves and sponges are not generally considered to be symbiotic as the host responds to their presence by forming physical barriers with an active growth edge in the exoskeleton isolating the invader and, at a subcellular level, activating innate immune responses such as melanin deposition. This study describes a novel symbiosis between a newly described hydrozoan (Zanclea margaritae sp. nov.) and the reef building coral Acropora muricata (=A. formosa), with the hydrozoan hydrorhiza ramifying throughout the coral tissues with no evidence of isolation or activation of the immune systems of the host. The hydrorhiza lacks a perisarc, which is typical of symbiotic species of this and related genera, including species that associate with other cnidarians such as octocorals. The symbiosis was observed at all sites investigated from two distant locations on the Great Barrier Reef, Australia, and appears to be host species specific, being found only in A. muricata and in none of 30 other species investigated at these sites. Not all colonies of A. muricata host the hydrozoans and both the prevalence within the coral population (mean = 66%) and density of emergent hydrozoan hydranths on the surface of the coral (mean = 4.3 cm⁻², but up to 52 cm⁻²) vary between sites. The form of the symbiosis in terms of the mutualism–parasitism continuum is not known, although the hydrozoan possesses large stenotele nematocysts, which may be important for defence from predators and protozoan pathogens. This finding expands the known A. muricata holobiont and the association must be taken into account in future when determining the corals’ abilities to defend against predators and withstand stress.     

Thecate stem medusozoans (Cnidaria) from the early Cambrian Chengjiang biota

Cnidarians are phylogenetically located near the base of the ‘tree of animals’, and their early evolution had a profound impact on the rise of bilaterians. However, the early diversity and phylogeny of this ‘lowly’ metazoan clade has hitherto been enigmatic. Fortunately, cnidarian fossils from the early Cambrian could provide key insights into their evolutionary history. Here, based on a scrutiny of the purported hyolith Burithes yunnanensis Hou et al. from the early Cambrian Chengjiang biota in South China, we reveal that this species shows characters distinct from those typical of hyoliths, not least a funnel-shaped gastrovascular system with a single opening, a whorl of tentacles surrounding the mouth, and the lack of an operculum. These characters suggest a great deviation from the original definition of the genus Burithes, and a closer affinity with cnidarians. We therefore reassign the material to a new genus: Palaeoconotuba. Bayesian inference of phylogeny based on new anatomical traits identifies a new clade, including Palaeoconotuba and Cambrorhytium, as a stem group of sessile medusozoan cnidarians that are united by the synapomorphies of developing an organic conical theca and a funnel-like gastrovascular system. This study unveils a stem lineage of medusozoans that evolved a lifelong conical theca in the early Cambrian.