A stem-group cnidarian described from the mid-Cambrian of China and its significance for cnidarian evolution

Palaeontological data of extinct groups often sheds light on the evolutionary sequences leading to extant groups, but has failed to resolve the basal metazoan phylogeny including the origin of the Cnidaria. Here we report the occurrence of a stem-group cnidarian, Cambroctoconus orientalis gen. et sp. nov., from the mid-Cambrian of China, which is a colonial organism with calcareous octagonal conical cup-shaped skeletons. It bears cnidarian features including longitudinal septa arranged in octoradial symmetry and colonial occurrence, but lacks a jelly-like mesenchyme. Such morphological characteristics suggest that the colonial occurrence with polyps of octoradial symmetry is the plesiomorphic condition of the Cnidaria and appeared earlier than the jelly-like mesenchyme during the course of evolution

The potential for coral reef establishment through free-living stabilization

Corals thrive in a variety of environments, from low wave and tidal energy lagoons, to high energy tidal reef flats, but remain dependent upon suitable substrate. Herein we reviewed the phenomenon of free-living corals (coralliths), examined whether they have the capacity to create their own stable habitat in otherwise uninhabitable, poor substrate environments through 'free-living stabilization', and explore their potential ecological role on coral reefs. This stabilization could be achieved by coral settlement and survival on mobile substrate, with subsequent growth into free-living coralliths until a critical mass is reached that prevents further movement. This allows for secondary reef colonization by other coral species. To preliminarily test this hypothesis we provide evidence that the potential to support secondary coral colonisation increases with corallith size. Due to the limited diversity of corallith species observed here and in the literature, and the lack of physiological differences exhibited by coralliths here to static controls, it seems likely that only a small selection of coral species have the ability to form coralliths, and the potential to create their own stable habitat

Global Diversity of the Stylasteridae (Cnidaria: Hydrozoa: Athecatae)

The history and rate of discovery of the 247 valid Recent stylasterid species are discussed and graphed, with emphasis on five historical pulses of species descriptions. A table listing all genera, their species numbers, and their bathymetric ranges are presented. The number of species in 19 oceanographic regions is mapped, the southwestern temperate Pacific (region including New Zealand) having the most species; species are cosmopolitan from the Arctic Circle to the Antarctic at depths from 0 to 2789 m. The current phylogenetic classification of the genera is briefly discussed. An illustrated glossary of 53 morphological characters is presented. Biological and ecological information pertaining to reproduction, development, commensals, and distribution is discussed. Aspects of stylasterid mineralogy and taxa of commercial value are discussed, concluding with suggestions for future work

Desmophyllum dianthus (Esper, 1794) in the scleractinian phylogeny and its intraspecific diversity

© The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in PLoS One 7 (2012): e50215, doi:10.1371/journal.pone.0050215.The cosmopolitan solitary deep-water scleractinian coral Desmophyllum dianthus (Esper, 1794) was selected as a representative model species of the polyphyletic Caryophylliidae family to (1) examine phylogenetic relationships with respect to the principal Scleractinia taxa, (2) check population structure, (3) test the widespread connectivity hypothesis and (4) assess the utility of different nuclear and mitochondrial markers currently in use. To carry out these goals, DNA sequence data from nuclear (ITS and 28S) and mitochondrial (16S and COI) markers were analyzed for several coral species and for Mediterranean populations of D. dianthus. Three phylogenetic methodologies (ML, MP and BI), based on data from the four molecular markers, all supported D. dianthus as clearly belonging to the “robust” clade, in which the species Lophelia pertusa and D. dianthus not only grouped together, but also shared haplotypes for some DNA markers. Molecular results also showed shared haplotypes among D. dianthus populations distributed in regions separated by several thousands of kilometers and by clear geographic barriers. These results could reflect limited molecular and morphological taxonomic resolution rather than real widespread connectivity. Additional studies are needed in order to find molecular markers and morphological features able to disentangle the complex phylogenetic relationship in the Order Scleractinia and to differentiate isolated populations, thus avoiding the homoplasy found in some morphological characters that are still considered in the literature.This study was funded by CTM2009-00496 and CGL2011-23306 projects of the “Ministerio de Ciencia e Innovación” (Spain). Research at sea was partly supported by the European Commission F. P.VI Project HERMES Contract No. GOCE-CT-2005-511234-1) and the EU F.P. VII Project HERMIONE(contract number no. 226354)

Contrasting Light Spectra Constrain the Macro and Microstructures of Scleractinian Corals

The morphological plasticity of scleractinian corals can be influenced by numerous factors in their natural environment. However, it is difficult to identify in situ the relative influence of a single biotic or abiotic factor, due to potential interactions between them. Light is considered as a major factor affecting coral skeleton morphology, due to their symbiotic relation with photosynthetic zooxanthellae. Nonetheless, most studies addressing the importance of light on coral morphological plasticity have focused on photosynthetically active radiation (PAR) intensity, with the effect of light spectra remaining largely unknown. The present study evaluated how different light spectra affect the skeleton macro- and microstructures in two coral species (Acropora formosa sensu Veron (2000) and Stylophora pistillata) maintained under controlled laboratory conditions. We tested the effect of three light treatments with the same PAR but with a distinct spectral emission: 1) T5 fluorescent lamps with blue emission; 2) Light Emitting Diodes (LED) with predominantly blue emission; and 3) Light Emitting Plasma (LEP) with full spectra emission. To exclude potential bias generated by genetic variability, the experiment was performed with clonal fragments for both species. After 6 months of experiment, it was possible to detect in coral fragments of both species exposed to different light spectra significant differences in morphometry (e.g., distance among corallites, corallite diameter, and theca thickness), as well as in the organization of their skeleton microstructure. The variability found in the skeleton macro- and microstructures of clonal organisms points to the potential pitfalls associated with the exclusive use of morphometry on coral taxonomy. Moreover, the identification of a single factor influencing the morphology of coral skeletons is relevant for coral aquaculture and can allow the optimization of reef restoration efforts

Microstructure of Common Reef-Building Coral Genera Acropora, Pocillopora, Goniastrea and Porites : Constraints on Spatial Resolution in Geochemical Sampling

Scleractinian corals are increasingly used as recorders of modern and paleoclimates. The microstructure of four common reef-building coral genera is documented here: Acropora, Pocillopora, Goniastrea, and Porites. This study highlights the complexity and spatial variability of skeletal growth in different coral genera and suggests that a single growth model is too generalized to allow the accurate depiction of the variability observed in the four genera studied. New models must be introduced in order for coral skeletogenesis to be understood adequately to allow coral skeletons to serve as repositories of temporally constrained geochemical data. Owing to differences in microstructural patterns in different genera, direct observation of microstructural elements and growth lines may be necessary to allow microsamples to be placed into series that represent temporal sequences with known degrees of time averaging. Such data are critical for constraining microsampling strategies aimed at developing true time series geochemical data at very fine spatial and temporal scales

Skeletal morphogenesis and growth mode of modern and fossil deep-water isidid gorgonians (Octocorallia) in the West Pacific (New Zealand and Sea of Okhotsk)

Fabric and growth mode of deep-water isidid gorgonian skeletons showing bright Mg-calcitic internodes and dark proteinageous nodes were investigated on modern, subrecent and fossil skeletons. The internodial microstructure is characterised by three-dimensionally interfingering calcitic fascicles accreting around a central axis. Macroscopic colour banding results from varying orientations of organic-rich fascicle bundles and intercalated bands of organic-poor granular crystals. This skeletal structure of isidid gorgonians strikingly differs from the density banding of scleractinians. Radiocarbon dating of a fossil skeleton gave an age of 3,985±35 to 3,680±35 years before present (BP) with a record of 305±35 years (±range). Linear extension rates of 0.4 mm year−1 average allow for an annual to sub-annual resolution on micrometer scale of colour bands or fascicles, respectively. The growth mode of branched skeletons is characterised by simultaneous secretion of vertically alternating nodes/internodes and lateral accretion of concentric increments enveloping the entire skeleton. Bifurcations at various growth stages imply that adjacent branches have different ages and show varying numbers of growth bands at any skeletal cross section. The scleroprotein gorgonin plays a crucial role in the formation of organic nodes and the secretion of calcitic internodes by providing a structural framework in the biomineralisation process