Echinoderm Skeletons Research Articles

Bio-Informed Porous Mineral-Based Composites.

Certain biominerals, such as sea sponges and echinoderm skeletons, display a fascinating combination of mechanical properties and adaptability due to the well-defined structures spanning various length scales. These materials often possess high density normalized mechanical properties because they contain well-defined pores. The density-normalized mechanical properties of synthetic minerals are often inferior because the pores are stochastically distributed, resulting in an inhomogeneous stress distribution. The mechanical properties of synthetic materials are limited by the degree of structural and compositional control currently available fabrication methods offer. In the first part of this review, examples of structural elements nature uses to impart exceptional density normalized Young's moduli to its porous biominerals are showcased. The second part highlights recent advancements in the fabrication of bio-informed mineral-based composites possessing pores with diameters that span a wide range of length scales. The influence of the processing of mineral-based composites on their structures and mechanical properties is summarized. Thereby, it is aimed at encouraging further research directed to the sustainable, energy-efficient fabrication of synthetic lightweight yet stiff mineral-based composites.

Composite material in the sea urchin Cidaris rugosa: ordered and disordered micrometre-scale bicontinuous geometries.

The sponge-like biomineralized calcite materials found in echinoderm skeletons are of interest in terms of both structure formation and biological function. Despite their crystalline atomic structure, they exhibit curved interfaces that have been related to known triply periodic minimal surfaces. Here, we investigate the endoskeleton of the sea urchin Cidaris rugosa that has long been known to form a microstructure related to the Primitive surface. Using X-ray tomography, we find that the endoskeleton is organized as a composite material consisting of domains of bicontinuous microstructures with different structural properties. We describe, for the first time, the co-occurrenceof orderedsingle Primitive and singleDiamond structures and of a disordered structure within a single skeletal plate. We show that these structures can be distinguished by structural properties including solid volume fraction, trabeculae width and, to a lesser extent, interface area and mean curvature. Indoing so, we present a robust method that extracts interface areas and curvature integrals from voxelized datasets using the Steiner polynomial for parallel body volumes. We discuss these very large-scale bicontinuous structures in the context of their function, formation and evolution.

A marine origin of coal balls in the Midland and Illinois basins, USA

Coal balls are carbonate concretions that preserve peat in cellular detail. Despite their importance to paleobotany, the salinity of coal-ball peat remains controversial. Pennsylvanian coal balls from the Midland and Illinois basins contain echinoderms and early high-magnesium calcite cement. Echinoderm skeletons reflect the Mg/Ca ratio of the seawater in which they grew. Here we show that well-preserved echinoderms in coal balls and North American Pennsylvanian marine facies have similar average mole % MgCO3; 10.2–12.3 and 9.9–12.5 respectively. Coal-ball echinoderms reflect the magnesium content of the adjacent epicontinental seawater. Early high-magnesium calcite cement in coal balls has the same, or more magnesium than echinoderms from the same deposit, and high Sr/Ca and Na/Ca, consistent with formation in marine or brackish water. Subsequent coal-ball cement is low-magnesium calcite, suggesting freshwater diagenesis and cementation followed formation of marine high-magnesium calcite. Coal balls likely formed in the marine-freshwater mixing zone.

Acorn worm ossicle ultrastructure and composition and the origin of the echinoderm skeleton.

Here, we describe the shape and mineral composition of ossicles from eight acorn worm species, bringing the total known biomineralizing enteropneusts to 10 and confirming that ossicles are widespread in Enteropneusta. Three general forms were identified including a globular form that occurs in all three major enteropneust families. The biomineral compositions included all three polymorphs of calcium carbonate; calcite, aragonite and vaterite, and low to high magnesium concentrations. Calcite was the most common and characteristic of echinoderm ossicles. Based on these findings we hypothesize that an enteropneust-like ancestor to the Ambulacraria had ectodermal ossicles, formed in an extracellular occluded space bordered by a sheath of sclerocyte cells. The ossicles were microscopic, monotypic globular shaped, calcite ossicles with low to high Mg content and MSP130 proteins. The ossicles lacked intercalation with other ossicles. The function of acorn worm ossicles is unknown, but the position of ossicles in the trunk epithelia and near to the surface suggests predator deterrence, to provide grip on the walls of a burrow or tube, as storage of metabolic waste, or to regulate blood pH, rather than as an endoskeleton function seen in fossil and crown group Echinodermata.

High‐Strength Hydroxyapatite Scaffolds with Minimal Surface Macrostructures for Load‐Bearing Bone Regeneration

AbstractTriply periodic minimum surfaces (TPMS), which outperform other structures in terms of bulk moduli and relative density, have been widely used to dramatically improve the mechanical strength of natural echinoderm skeletons and engineered scaffolds. Herein, TPMS‐structure‐based 3D‐printed hydroxyapatite (HAp) scaffolds to highly improve their limited mechanical strength and evaluate the underlying mechanism in terms of mechanical match and biological bone repair process as a bone regeneration scaffold are constructed. The results show that TPMS‐structure‐based HAp scaffolds have a greater compressive strength range that is sufficient to meet the strength requirements for human cortical and trabecular bone, and outperform traditional HAp scaffolds with Cross‐hatch structures in terms of compressive strength, cell density, and osteogenic differentiation. The reduction of stress concentration and open‐cell permeable structure of Split‐P scaffolds can benefit the generation and ingrowth of new bone after the in vivo implantation in the rabbit femur bone. Furthermore, RNA‐seq and immunochemistry staining results of in vivo samples unravel the bone repair mechanism in a time sequence. The optimized scaffolds with TPMS macrostructures and an in‐depth understanding of repair mechanisms will contribute to the development of bone regeneration materials that perform on par with load‐bearing bone.

Cambrian edrioasteroid reveals new mechanism for secondary reduction of the skeleton in echinoderms.

Echinoderms are characterized by a distinctive high-magnesium calcite endoskeleton as adults, but elements of this have been drastically reduced in some groups. Herein, we describe a new pentaradial echinoderm, Yorkicystis haefneri n. gen. n. sp., which provides, to our knowledge, the oldest evidence of secondary non-mineralization of the echinoderm skeleton. This material was collected from the Cambrian Kinzers Formation in York (Pennsylvania, USA) and is dated as ca 510 Ma. Detailed morphological observations demonstrate that the ambulacra (i.e. axial region) are composed of flooring and cover plates, but the rest of the body (i.e. extraxial region) is preserved as a dark film and lacks any evidence of skeletal plating. Moreover, X-ray fluorescence analysis reveals that the axial region is elevated in iron. Based on our morphological and chemical data and on taphonomic comparisons with other fossils from the Kinzers Formation, we infer that the axial region was originally calcified, while the extraxial region was non-mineralized. Phylogenetic analyses recover Yorkicystis as an edrioasteroid, indicating that this partial absence of skeleton resulted from a secondary reduction. We hypothesize that skeletal reduction resulted from lack of expression of the skeletogenic gene regulatory network in the extraxial body wall during development. Secondary reduction of the skeleton in Yorkicystis might have allowed for greater flexibility of the body wall.

Impact of seawater Mg2+/Ca2+ on Mg/Ca of asterozoan skeleton – Evidence from culturing and the fossil record

Skeletal Mg/Ca in echinoderms is thought to be related to ambient seawater Mg2+/Ca2+ ratio, which prompts the use of well-preserved fossil echinoderms as paleoseawater Mg2+/Ca2+ proxies. Nonetheless, experimental studies testing the effect of seawater Mg2+/Ca2+ ratio on echinoderm skeleton are limited to one echinoderm class, i.e., sea urchins (echinoids). Here, we investigated the effect of decreased seawater Mg2+/Ca2+ ratio on skeletal composition (Mg/Ca ratio) of a sea star Asterias rubens and a brittle star Ophiocomina nigra. Specimens were tagged with manganese and then cultured under three different Mg2+/Ca2+ molar ratios (~5.2, ~2.5, ~1.5 mol/mol) in order to simulate variations of ambient seawater Mg2+/Ca2+ ratio that existed throughout the Phanerozoic. Decreased Mg2+/Ca2+ in seawater did not affect the respiration rates or inhibit calcification of sea stars, which suggests that they were not significantly stressed by the treatment. It did, however, clearly affect growth and mortality in brittle stars, for which reliable geochemical data could not be obtained. Under decreased seawater Mg2+/Ca2+ sea stars produced a skeleton with decreased Mg/Ca ratio. This is consistent with the hypothesis that the skeletal chemistry in echinoderms is influenced by seawater chemistry and, consequently, that fossil echinoderms may preserve a record of paleoseawater Mg2+/Ca2+. Although our data from well-preserved fossil sea stars from the Middle Jurassic and Miocene are consistent with low Mg2+/Ca2+ ratio of the Jurassic "calcite sea" and high Mg2+/Ca2+ ratio of the Miocene "aragonite sea", the accuracy of paleoseawater Mg2+/Ca2+ reconstructions from fossil echinoderms is limited by the fact that Mg partition coefficients vary significantly between different echinoderm species.

Effects of seawater Mg2+ /Ca2+ ratio and diet on the biomineralization and growth of sea urchins and the relevance of fossil echinoderms to paleoenvironmental reconstructions.

It has been argued that skeletal Mg/Ca ratio in echinoderms is mostly governed by Mg2+ and Ca2+ concentrations in the ambient seawater. Accordingly, well-preserved fossil echinoderms were used to reconstruct Phanerozoic seawater Mg2+ /Ca2+ ratio. However, Mg/Ca ratio in echinoderm skeleton can be affected by a number of environmental and physiological factors, the effects of which are still poorly understood. Notably, experimental data supporting the applicability of echinoderms in paleoenvironmental reconstructions remain limited. Here, we investigated the effect of ambient Mg2+ /Ca2+ seawater ratio and diet on skeletal Mg/Ca ratio and growth rate in two echinoid species (Psammechinus miliaris and Prionocidaris baculosa). Sea urchins were tagged with manganese and then cultured in different Mg2+ /Ca2+ conditions to simulate fluctuations in the Mg2+ /Ca2+ seawater ratios in the Phanerozoic. Simultaneously, they were fed on a diet containing different amounts of magnesium. Our results show that the skeletal Mg/Ca ratio in both species varied not only between ossicle types but also between different types of stereom within a single ossicle. Importantly, the skeletal Mg/Ca ratio in both species decreased proportionally with decreasing seawater Mg2+ /Ca2+ ratio. However, sea urchins feeding on Mg-enriched diet produced a skeleton with a higher Mg/Ca ratio. We also found that although incubation in lower ambient Mg2+ /Ca2+ ratio did not affect echinoid respiration rates, it led to a decrease or inhibition of their growth. Overall, these results demonstrate that although skeletal Mg/Ca ratios in echinoderms can be largely determined by seawater chemistry, the type of diet may also influence skeletal geochemistry, which imposes constraints on the application of fossil echinoderms as a reliable proxy. The accuracy of paleoseawater Mg2+ /Ca2+ calculations is further limited by the fact that Mg partition coefficients vary significantly at different scales (between species, specimens feeding on different types of food, different ossicle types, and stereom types within a single ossicle).

Minor and trace elements in skeletons of Arctic echinoderms

We report the ratios of minor (K/Ca, Na/Ca, P/Ca, S/Ca) and trace elements (Al/Ca, Ba/Ca, Fe/Ca, Mn/Ca and Zn/Ca) in skeletons of five Arctic echinoderm species representing three classes: Asteroidea, Ophiuroidea, Crinoidea. We found that skeletons of Arctic echinoderms show a unique, species-specific trace element composition that may suggest that incorporation of elements into the skeleton is biologically controlled by the organism. On the other hand, the concentration of some minor elements in skeletal parts exhibit patterns that are consistent with elemental concentrations in seawater, indicating that formation of echinoderm skeletons is environmentally controlled. Seawater is the main source of ions and compounds needed for skeletal formation and maintaining similar concentrations most likely reduces the biological cost related to selective uptake of ions. Additionally, Al, Ba, Fe, Mg and Mn showed station specific variation in elemental concentration which again suggests that accumulation of metals can be shaped by environmental concentrations.

Quantitative 3D structural analysis of the cellular microstructure of sea urchin spines (I): Methodology

The mineralized skeletons of echinoderms are characterized by their complex, open-cell porous microstructure (also known as stereom), which exhibits vast variations in pore sizes, branch morphology, and three-dimensional (3D) organization patterns among different species. Quantitative description and analysis of these cellular structures in 3D are needed in order to understand their mechanical properties and underlying design strategies. In this paper series, we present a framework for analyzing such structures based on high-resolution 3D tomography data and utilize this framework to investigate the structural designs of stereom by using the spines from the sea urchin Heterocentrotus mamillatus as a model system. The first paper here reports the proposed cellular network analysis framework, which consists of five major steps: synchrotron-based tomography and hierarchical convolutional neural network-based reconstruction, machine learning-based segmentation, cellular network registration, feature extraction, and data representation and analysis. This framework enables the characterization of the porous stereom structures at the individual node and branch level (~10 µm), the local cellular level (~100 µm), and the global network level (~1 mm). We define and quantify multiple structural descriptors at each level, such as node connectivity, branch length and orientation, branch profile, ring structure, etc., which allows us to investigate the cellular network construction of H. mamillatus spines quantitatively. The methodology reported here could be tailored to analyze other natural or engineering open-cell porous materials for a comprehensive multiscale network representation and mechanical analysis. Statement of SignificanceThe mechanical robustness of the biomineralized porous structures in sea urchin spines has long been recognized. However, quantitative cellular network representation and analysis of this class of natural cellular solids are still limited in the literature. This constrains our capability to fully understand the mechanical properties and design strategies in sea urchin spines and other similar echinoderms’ porous skeletal structures. Combining high-resolution tomography and computer vision-based analysis, this work presents a multiscale 3D network analysis framework, which allows for extraction, registration, and quantification of sea urchin spines’ complex porous structure from the individual branch and node level to the global network level. This 3D structural analysis is relevant to a diversity of research fields, such as biomineralization, skeletal biology, biomimetics, material science, etc.

Hydrothermal synthesis of Mg-substituted tricalcium phosphate nanocrystals

Abstract

Morphology, shape variation and movement of skeletal elements in starfish (Asterias rubens).

Starfish (order: Asteroidea) possess a complex endoskeleton composed of thousands of calcareous ossicles. These ossicles are embedded in a body wall mostly consisting of a complex collagen fiber array. The combination of soft and hard tissue provides a challenge for detailed morphological and histological studies. As a consequence, very little is known about the general biomechanics of echinoderm endoskeletons and the possible role of ossicle shape in enabling or limiting skeletal movements. In this study, we used high-resolution X-ray microscopy to investigate individual ossicle shape in unprecedented detail. Our results show the variation of ossicle shape within ossicles of marginal, reticular and carinal type. Based on these results we propose an additional classification to categorize ossicles not only by shape but also by function into 'connecting' and 'node' ossicles. We also used soft tissue staining with phosphotungstic acid successfully and were able to visualize the ossicle ultrastructure at 2-μm resolution. We also identified two new joint types in the aboral skeleton (groove-on-groove joint) and between adambulacral ossicles (ball-and-socket joint). To demonstrate the possibilities of micro-computed tomographic methods in analyzing the biomechanics of echinoderm skeletons we exemplarily quantified changes in ossicle orientation for a bent ray for ambulacral ossicles. This study provides a first step for future biomechanical studies focusing on the interaction of ossicles and soft tissues during ray movements.

Effects of seawater chemistry (Mg2+/Ca2+ ratio) and diet on the skeletal Mg/Ca ratio in the common sea urchin Paracentrotus lividus

It has been argued that concentration of major metallic ions such as Mg2+ and Ca2+ plays a role in determining the composition of the echinoderm skeleton. Consequently, in several studies Mg/Ca ratio from modern and fossil echinoderm ossicles was used as a proxy of secular Mg2+/Ca2+ changes of Phanerozoic seawater. However, although significant progress has been made in understanding biomineralization of echinoderms, it is still largely unknown what are the sources and physiological pathways of major ions that contribute to skeleton formation. Herein we tested the effects of modifications of ambient seawater Mg2+/Ca2+ ratio (which is typically ∼5) and Mg-enrichment of the diet on the Mg/Ca ratio in regenerating spines of sea urchin Paracentrotus lividus under experimental conditions. We found that sea urchins cultured in seawater with Mg2+/Ca2+ ratio decreased to ∼1.9 produced a skeleton with also decreased Mg/Ca ratio. However, the skeleton of specimens fed on a Mg-enriched diet showed significantly higher Mg/Ca ratio. This suggests that the seawater is an important but not the only source of ions that contributes to the Mg/Ca ratio of the skeleton. Consequently, the reliability of geochemical models that link directly seawater chemistry with the Mg/Ca ratio of the skeleton should be reevaluated.

Echinoid skeletal carbonate as archive of past seawater magnesium isotope signatures – Potential and limitations

The low-Mg (spine) to high-Mg (test) calcite skeletal hardparts of echinoids are exploited in carbonate archive research. These studies, however, are not coming without problems. Those rise from the solid phase metastability, the presence of amorphous precursors during biomineralization processes, the spatially variable skeletal Mg concentrations, and the porous microstructure at secretion of these biominerals. The present paper systematically evaluates the resilience of echinoid skeletal hardparts, here specifically sea urchin spines, to diagenetic alteration with a focus on magnesium isotope distribution (δ26Mg). We apply a dual approach by (i) performing alteration experiments using meteoric, marine, and burial model fluids and by (ii) comparing the experimental data with diagenetically overprinted fossil sea urchin hardparts. The degree of alteration of individual spines and an echinoid test was assessed by a combination of optical (fluorescence, cathodoluminescence (CL), scanning electron microscopy (SEM)) and geochemical tools (elemental distribution and δ26Mg). Magnesium isotope signatures of sea urchin spines are affected by experimental temperature, fluid composition, and duration of alteration experiment. Most strikingly, the recrystallization of spines from low-Mg (<5 mol% Mg fraction) to high-Mg or highest-Mg calcite (>5 up to 44 mol%) is observed throughout the experiments using burial and marine fluids at 175 °C. Simultaneously, δ26Mg values of progressively recrystallized Mg calcite are increasingly enriched in 26Mg. Fossil spine material displays the highest Mg/Ca ratios and highest δ26Mg values, whereas a fossil (diagenetically overprinted) sea urchin test, formerly high-Mg and subsequently recrystallized to low-Mg calcite, displays the lowest δ26Mg values. These diagenetic features are in agreement with the data obtained from experimentally altered spines. The transformation of low- to high-Mg calcite of altered sea urchin hardparts is essentially controlled by the Mg content of the diagenetic fluid and directly affects the Mg isotope signature of the echinoderm skeleton. The experimental alteration data presented here mimic the patterns of Mg/Ca ratios and Mg isotope signatures of fossil echinoid skeletal hardparts as induced by diagenesis. Both, Mg/Ca ratios and isotope signatures of echinoderm hardparts are spatially and ontogenetically complex to start with and undergo significant and variable (fluid and carbonate composition-dependent) alteration processes in the presence of diagenetic fluids. These alteration processes include dissolution and re-precipitation reactions, but also diffusion between bulk and pore solution within the pore system of the sea urchin spine. The research shown here is significant as it documents the potential of a combined study using naturally and experimentally altered carbonate hardparts in an exemplary manner. Clearly, a critical approach to echinoid proxy archive for the reconstruction of past seawater Mg isotope composition is advised. In contrast, Mg isotope data and their changes in time and space have a significant potential to document processes and products resulting from diagenesis.

Eggs for breakfast? Analysis of a probable mosasaur biting trace on the Cretaceous echinoid &amp;lt;i&amp;gt;Echinocorys ovata&amp;lt;/i&amp;gt; Leske, 1778

Abstract. Fossil biting traces (praedichnia) represent indirect evidence of predation and shed light on fossil predator–prey interactions and fossil food webs. Especially from echinoderm skeletons, biting traces are well known. Here, we describe the oral surface of a large Cretaceous (Maastrichtian) holasteroid echinoid Echinocorys ovata Leske, 1778 from Hemmoor (northern Germany) which exhibits four circular punctures arranged in a semi-circular arc. Whereas three of the punctures penetrated the skeleton, one puncture only just hit the margin of the echinoid test at the ambitus, leaving a long incision furrow in the skeleton. The punctures were not lethal to the sea urchin as is indicated by progressed skeletal regeneration and closure of the fractures. The overall appearance of the punctures suggests that they were produced during a single mechanical event, most likely by the biting action of the teeth of a large vertebrate animal. We analysed the shape and arrangement of the biting trace and conclude that it was probably produced by a marine reptile possessing a prognath tooth position, most likely by a globidensine mosasauroid. Our finding not only sheds light on mosasaur feeding behaviour and prey selection but also increases the knowledge of the food webs in the chalk sea ecosystem during the uppermost Cretaceous.

The evolution of mollusc shells

Molluscan shells are externally fabricated by specialized epithelial cells on the dorsal mantle. Although a conserved set of regulatory genes appears to underlie specification of mantle progenitor cells, the genes that contribute to the formation of the mature shell are incredibly diverse. Recent comparative analyses of mantle transcriptomes and shell proteomes of gastropods and bivalves are consistent with shell diversity being underpinned by a rapidly evolving mantle secretome (suite of genes expressed in the mantle that encode secreted proteins) that is the product of (a) high rates of gene co-option into and loss from the mantle gene regulatory network, and (b) the rapid evolution of coding sequences, particular those encoding repetitive low complexity domains. Outside a few conserved genes, such as carbonic anhydrase, a so-called "biomineralization toolkit" has yet to be discovered. Despite this, a common suite of protein domains, which are often associated with the extracellular matrix and immunity, appear to have been independently and often uniquely co-opted into the mantle secretomes of different species. The evolvability of the mantle secretome provides a molecular explanation for the evolution and diversity of molluscan shells. These genomic processes are likely to underlie the evolution of other animal biominerals, including coral and echinoderm skeletons. This article is categorized under: Comparative Development and Evolution > Regulation of Organ Diversity Comparative Development and Evolution > Evolutionary Novelties.

Inter and intraspecific comparisons of the skeletal Mg/Ca ratios of high latitude Antarctic echinoderms

AbstractEchinoderms are vulnerable to ocean acidification because of their high magnesium calcite skeletons. Here, skeletal Mg/Ca ratios were examined within and between individuals of 20 Antarctic echinoderms representative of the asteroids, ophiuroids and echinoids. The highest mean Mg/Ca ratios occurred in the discs and arms (0.111 and 0.110, respectively) of brittle-stars and the lowest in the spines (0.010) of cidaroid sea urchins. Many taxa (11 of 14 species) from the collection sites showed no intraspecific differences in Mg/Ca ratios between given skeletal components. Exceptions were the spines of two regular sea urchins and the skeletal ossicles of the combined arms and disc of a brittle-star. The relationship between skeletal magnesium content and latitude was further evaluated and an inverse correlation was found between Antarctic echinoderm taxa skeletal magnesium content and latitude across 62° to 76°, indicating that the relationship occurs over relatively narrow latitudes. Upon examination of an even narrower range (70–76° latitude), a region where the mineralogy of echinoderm skeletons has not been investigated, the predicted inverse relationship between Mg/Ca ratio and latitude was still observed in sea-stars, but not in brittle-stars or sea urchins.

Mg and Sr in Arctic echinoderm calcite: Nature or nurture?

Abstract The Mg/Ca and Sr/Ca ratios in echinoderm skeletal calcite are used as a proxy for Phanerozoic seawater changes, since the skeletal concentrations are, to some extent, controlled by environmental factors. However, it remains unclear how the influence of environmental factors is modified by vital effects, especially in polar waters. Therefore, the goal of this study was to compare the ratios of Mg/Ca and Sr/Ca among the skeletal parts of 10 common Arctic echinoderm species belonging to three classes Echinoidea, Asteroidea and Ophiuroidea that contribute substantially to the carbon cycle in the Arctic benthic system. Significant differences were recorded in echinoid skeletal element concentrations among specific skeletal parts. The lowest Mg/Ca and Sr/Ca ratios were detected in the spines (mean Mg/Ca 37.5 ± 8.8 SD; Sr/Ca 1.8 ± 0.1). The components of the Aristotle's lantern (epiphyses, pyramids and rotulas) were characterised by the highest Mg levels (Mg/Ca 79.9 ± 6.0; 75.2 ± 9.1; 60.1 ± 3.8, respectively). It is likely that mouth parts experience greater mechanical pressure compared to other body parts, and the higher content of Mg in the Aristotle's lantern contributes to its robustness. We did not find any distinctive trends in the distribution of skeletal elements in the asteroid and ophiuroid skeletal parts. The heterogeneous concentrations of Mg and Sr in different skeleton parts of the echinoids suggest possible physiological regulation of the chemical composition rather than the composition only being influenced by the environment. We cannot recommend echinoderm skeletons as reliable indicators in palaeoenvironmental reconstructions due to the possible biological control of skeletal chemistry, which may interfere with the effect of environmental variables.

Variability in magnesium content in Arctic echinoderm skeletons

In this study, 235 measurements of magnesium concentration in echinoderm's skeletons were compiled, including 30 species and 216 specimens collected from northern and western Barents Sea. We aimed to reveal the scale of Mg variation in the skeletons of Arctic echinoderms. Furthermore, we attempted to examine whether the Mg concentration in echinoderm skeletons is determined primarily by biological factors or is a passive result of environmental influences. We found that the Mg concentration in echinoderm skeletons was characteristic for particular echinoderm classes or was even species-specific. The highest Mg contents were observed in asteroids, followed by ophiuroids, crinoids, and holothuroids, with the lowest values in echinoids. These results strongly imply that biological factors play an important role in controlling the incorporation of Mg into the skeletons of the studied individuals.

The skeletal proteome of the sea star Patiria miniata and evolution of biomineralization in echinoderms

BackgroundProteomic studies of skeletal proteins have revealed large, complex mixtures of proteins occluded within the mineral. Many skeletal proteomes contain rapidly evolving proteins with repetitive domains, further complicating our understanding. In echinoderms, proteomic analysis of the skeletal proteomes of mineralized tissues of the sea urchin Strongylocentrotus purpuratus prominently featured spicule matrix proteins with repetitive sequences linked to a C-type lectin domain. A comparative study of the brittle star Ophiocoma wendtii skeletal proteome revealed an order of magnitude fewer proteins containing C-type lectin domains. A number of other proteins conserved in the skeletons of the two groups were identified. Here we report the complete skeletal proteome of the sea star Patiria miniata and compare it to that of the other echinoderm groups.ResultsWe have identified eighty-five proteins in the P. miniata skeletal proteome. Forty-two percent of the proteins were determined to be homologous to proteins found in the S. purpuratus skeletal proteomes. An additional 34 % were from similar functional classes as proteins in the urchin proteomes. Thirteen percent of the P. miniata proteins had homologues in the O. wendtii skeletal proteome with an additional 29% showing similarity to brittle star skeletal proteins. The P. miniata skeletal proteome did not contain any proteins with C-lectin domains or with acidic repetitive regions similar to the sea urchin or brittle star spicule matrix proteins. MSP130 proteins were also not found. We did identify a number of proteins homologous between the three groups. Some of the highly conserved proteins found in echinoderm skeletons have also been identified in vertebrate skeletons.ConclusionsThe presence of proteins conserved in the skeleton in three different echinoderm groups indicates these proteins are important in skeleton formation. That a number of these proteins are involved in skeleton formation in vertebrates suggests a common origin for some of the fundamental processes co-opted for skeleton formation in deuterostomes. The proteins we identify suggest transport of proteins and calcium via endosomes was co-opted to this function in a convergent fashion. Our data also indicate that modifications to the process of skeleton formation can occur through independent co-option of proteins following species divergence as well as through domain shuffling.