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The crystals in animal biominerals such as sea urchin spines, mollusk shells, and coral skeletons, form by attachment of amorphous particles that subsequently crystallize. Do these solid amorphous precursor particles have liquid precursors? Polymer-induced liquid precursors (PILP), or prenucleation clusters coalescing into a liquid precursor to calcium carbonate crystallization have been observed extensively in synthetic systems. Molecular dynamics simulations also predict liquid-liquid phase separation. However, evidence for liquid precursors in natural biominerals remains elusive. Here we present Scanning or PhotoEmission Electron Microscopy (SEM, PEEM) evidence consistent with a dense liquid-like precursor in regenerating sea urchin spines. The observed precursor originates in tissue and ultimately transforms into a single crystal of calcite (CaCO3) with complex stereom morphology.

In this paper, the effect of stereom structure on the mechanical behavior of the Sea Urchin Inorganic Skeleton (SUIS) has been studied. The stereom microstructure of both Anthocidaris crassispina and Tripnenstes gratilla was characterized by Scanning Electron Microscopy (SEM). Results indicate that a three-layer porous structure consisting of a growth, a support, and a resorption (GSR) layer is a common denominator for both species. The effect of GSR layer order on the mechanical behavior of the SUIS was studied by a finite element method. The results show that the GSR model could effectively reduce the maximum tensile stress on its meridional sutures under unidirectional pressure, hydrostatic pressure, and self-weight situation. For a fabricated three-layered ceramic test strips with different layer orders, the mechanical properties have a completely opposite performance compared with the compressive properties of the calculated SUIS-like models. This indicates that the GSR structure can effectively improve the mechanical properties of the SUIS, but it cannot be applied to bionics without considering its synergistic effect with the macro-structure of the SUIS. This is a typical example of bionic invalidation by single structure, where multi-level structure bionics may be an effective solution.

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 Significance The 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.

Repeated polygonal patterns are pervasive in natural forms and structures. These patterns provide inherent structural stability while optimizing strength-per-weight and minimizing construction costs. In echinoids (sea urchins), a visible regularity can be found in the endoskeleton, consisting of a lightweight and resistant micro-trabecular meshwork (stereom). This foam-like structure follows an intrinsic geometrical pattern that has never been investigated. This study aims to analyse and describe it by focusing on the boss of tubercles-spine attachment sites subject to strong mechanical stresses-in the common sea urchin Paracentrotus lividus. The boss microstructure was identified as a Voronoi construction characterized by 82% concordance to the computed Voronoi models, a prevalence of hexagonal polygons, and a regularly organized seed distribution. This pattern is interpreted as an evolutionary solution for the construction of the echinoid skeleton using a lightweight microstructural design that optimizes the trabecular arrangement, maximizes the structural strength and minimizes the metabolic costs of secreting calcitic stereom. Hence, this identification is particularly valuable to improve the understanding of the mechanical function of the stereom as well as to effectively model and reconstruct similar structures in view of future applications in biomimetic technologies and designs.

Living crinoids are exclusively passive suspension feeders and benthic as adults. However, in the past they adapted to a broad range of ecological niches. For instance, the stratigraphically important middle Paleozoic scyphocrinoids are hypothesized to have been planktonic, employing their inferred gas-filled globular, chambered structure at the distal end of the stem, the so-called lobolith, as a buoyancy device with the crinoid calyx suspended below it. Here, we evaluate this hypothesis using evidence from skeletal micromorphology and theoretical biomechanical modeling. Lobolith walls are typically composed of ossicles, which are exclusively composed of constructional labyrinthic stereom. In plates from the distal side of the lobolith, this stereom extends into microperforate stereom layer, forming wavy ridges and spines. No microscale adaptations for preventing gas leaks and/or ingress of water (such as internal and external imperforate stereom layers) are known. Furthermore, theoretical calculations suggest that the scyphocrinoid tow-net mode of feeding would have resulted in small relative velocities between the towed filter and the ambient water, thus making it an ineffective passive filter feeder. We suggest that the lobolith of these crinoids acted as a modified holdfast rather than as a floating buoy. Its globular shape and distally positioned microspines served as adaptations for living in unconsolidated sediments, analogous to iceberg- and snowshoe-like strategies used by some mollusks and brachiopods. Like modern isocrinids, scyphocrinoids could have maintained an upright feeding posture by extending the distal portion of the stalk along the bottom. In this recumbent posture, the distal part of the stalk with the lobolith might have functioned as a drag anchor. As a consequence of the ~3-m-long stem, even with this posture, the benthic scyphocrinoids could have risen to the highest epifaunal tier in the Paleozoic.

Three incomplete thecae of the stylophoran Lagynocystis cf. pyramidalis (Barrande, 1887) are described from the Upper Ordovician of the Baltic Paleobasin for the first time. These specimens of Lagynocystis are the first records of this genus from the Ordovician outside peri-Gondwana, thus significantly expanding its paleogeographical distribution of this genus. Due to the preservation of the specimens the microstructure of the stereom is studied for the first time in this genus.

A hardground surface in the middle Silurian (Wenlock: Sheinwoodian) Massie Formation is well exposed at the New Point stone quarry in Napoleon, southeastern Indiana, USA, where it is densely encrusted by pelmatozoan echinoderm attachment structures. Among the most common attachment structures encrusting the hardground are terminal dendritic radix structures attributable to the monobathrid camerate crinoid Eucalyptocrinites and the hemicosmitid rhombiferan Caryocrinites. Radicles belonging to both of these genera are often modified by secretion of secondary stereom, resulting in swollen, irregular calcitic masses that extend onto the substrate and can engulf nearby bioclasts. Herein, we describe a specimen that resembles a portion of a swollen radicular attachment structure; however, close inspection reveals that is actually an interaction between radicles of Caryocrinites and Eucalyptocrinites, as indicated by the presence of both a trilobate lumen, characteristic of Caryocrinites, as well as a pentalobate lumen, characteristic of Eucalyptocrinites. Hence, what appears to be part of a single structure is actually parts of two interwoven structures belonging to entirely different taxa. Increased attention to echinoderm attachment structures consisting of overgrowths and secondarily mineralized radicles may result in recognition of additional specimens that represent analogous biotic interactions rather than simple holdfast occurrences.

Introduction: The sea star odontophore is the structure positioned between the paired oral ossicles, with which they articulate through proximal and distal processes. The internal anatomy structures may be used as taxonomic characters for a precise differentiation between species, so it is necessary to describe the structures variation throughout growth. Objective: To describe the odontophore shape and variation of Luidia superba A. H. Clark, 1917 from specimens of the Gulf of California deposited in the Echinoderm National Collection, ICML UNAM. Methods: A total of 735 specimens were examined to describe the external characters, from which 55 selected specimens, within a range of R = 14 mm and R = 210 mm, were dissected to extract the odontophores and analyzed with geometric morphometrics. Results: Scanning electronic microscopy (SEM) images of the odontophores showing the variations in shape throughout growth are presented. Differences in shape between size groups were confirmed with a Canonical Variables Analysis (P < 0.05). Conclusions: There are three main groups in this size ranges where specialization of the stereom can be observed through the ontogenetic series; the variation in shape of the odontophore shown here is a precedent for the use of internal anatomy as new taxonomic characters of identification. Resumen Introducción: El odontóforo es la estructura posicionada entre las placas orales pareadas con las que se articula a través de procesos proximales y distales. Las estructuras de la anatomía interna se pueden usar como caracteres taxonómicos para la diferenciación más precisa entre especies, por lo que es necesario describir la variación de las estructuras a lo largo del crecimiento. Objetivo: Describir la forma y la variación del odontóforo de Luidia superba A. H. Clark, 1917 de ejemplares del Golfo de California depositados en la Colección Nacional de Equinodermos, ICML UNAM. Métodos: Se revisaron un total de 735 ejemplares para describir los caracteres externos y de las cuales se seleccionaron 55 ejemplares, dentro de un intervalo de R = 14 mm a R = 210 mm, de los cuales se extrajeron los odontóforos y fueron analizados utilizando morfometría geométrica. Resultados: Se presentan imágenes de microscopía electrónica de barrido (MEB) de los odontóforos que muestran las variaciones de la forma durante el crecimiento. Se confirmaron diferencias significativas de la forma entre los grupos de tallas mediante un CVA (p< 0.05). Conclusiones: Se observa especialización del estereoma a lo largo de la serie ontogenética; la variación en la forma del odontóforo aquí mostrada es precedente para el uso de estructuras de la anatomía interna como nuevos caracteres de identificación.

Echinoderms have a high-magnesium calcite skeleton whose cristallographie, chemical, and morphological properties make it different from abiotic calcites. The available data show that the single crystal behaviour, the conchoidal fracture properties, the high-magnesium content, and the stereom structure could be partly explained by the properties of the organic macromolecules associated with the mineral phase. Data suggest that these compounds could produce the stereom properties through stereochemical interactions with calcite.

Examination of nearly 500 specimens of Mitrocystites mitra, and Mitrocystella incipiens from the Lower Ordovician of Bohemia housed in the Barrande and Hanus collections of the National Museum, Prague, Czech Republic and new material from the Horǎk Museum, Rokycany, has yielded a wealth of new morphological data. Peripores and lateripores in M.mitra are surrounded by fine-mesh stereom clearly indicating they are sutural pores in origin. Internal tubular structures associated with these pores are probably gonadal in function; not eyes (pores) and nervous system as viewed in Jefferies’ ‘concept Calcichordata’. Both M.mitra and M. incipiens have a unique fully plated cloaca associate with the digit-like anal valvular plates. Mitrocystella incipiens, in some specimens, retains vestigial lateripores and the newly discovered aulacophore is longer than the theca. Within the Mitrocystitidae we can observe the possession and loss of basic echinoderm structures i.e. external hydropore and sutural pores. In addition, stereom construction of the plates, sutural pore systems, and well developed anal valves are thecal characters shared with the Blastozoa.

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).

The sea urchin test is composed of individual plates linked to each other in vertical and horizontal sutures either by connective tissue forming a flexible test or by skeletal processes and collagen fibres forming a rigid test. Musculature attached to the internal stereom of the test is restricted to: 1) ambulacral, peristomial and lantern muscles, e.g. in flexible sea urchins: 2) peristomial and lantern muscles, e.g. in rigid sea urchins with lantern and teeth; and 3) peristomial muscles, e.g. in rigid sea urchins without lantern and teeth. The internal muscles in the flexible test function as a pump. The lantern muscles function as a pump and take part in the feeding mechanism. The respiratory organs in sea urchins are specialized tube feet adapically situated on the test, and (’gills') orally situated on the test. One of the functions of the internal musculature in sea urchins is to pump oxygenated fluid from the respiratory organs to different parts of the body. In addition, the lantern muscles are part of the feeding mechanism.

Simple Summary Arbacia lixula, Paracentrotus lividus and Sphaerechinus granularis play a key role in many sublittoral biocommunities of the Mediterranean Sea. However, their skeletons seem to differ, both morphologically and in chemical composition. Thus, the skeletal elements display different properties, which are affected not only by the environment, but also by the vital effect of each species. We studied the microstructural morphology and crystalline phase of the test and spines, while also examining the effect of time on their elemental composition. Results showed morphologic differences among the three species both in spines and tests. They also seem to respond differently to possible time-related changes. The mineralogical composition of P. lividus appears to be quite different compare to the other two species. The results of the present study may contribute to a better understanding of the skeletal properties of these species, this being especially useful in predicting the effects of ocean acidification. More specifically, since the skeleton plays a key role for the survival of sea urchins in general, a potential change in any skeletal structure, either morphologically or chemically, may affect these organisms directly while also affecting their ecosystem indirectly. Abstract In the Mediterranean Sea, the species Arbacia lixula, Paracentrotus lividus and Sphaerechinus granularis often coexist, occupying different subareas of the same habitat. The mechanical and chemical properties of their calcitic skeletons are affected both by their microstructural morphology and chemical composition. The present study describes the main morphologic features and the possible temporal differences in elemental composition of the test and spines of the three species, while also determining the molar ratio of each element of their crystalline phase. Scanning electron microscopy showed major differences in the ultrastructure of the spines, while minor differences in the test were also noticed. More specifically, the spines of all three sea urchins possess wedges, however A. lixula exhibits bridges connecting each wedge, while barbs are observed in the wedges of S. granularis. The spines of P. lividus are devoid of both microstructures. Secondary tubercles are absent in the test of A. lixula, while the tests and spines of all three species are characterized by different superficial stereom. Energy dispersive x-ray spectroscopy detected that Ca, Mg, S, Na and Cl were present in all specimen. Mg and Mg/Ca showed significant differences between species both in test and spines with S. granularis having the highest concentration. The spines of P. lividus exhibited lowest values between all species. Differences between spines and test were observed in all elements for P. lividus except S. A. lixula exhibited different concentrations between test and spines for Ca, Mg and Mg/Ca, whereas S. granularis for Mg, Cl and Mg/Ca. Finally, temporal differences for Ca were observed in the test of P. lividus and the spines of S. granularis, for Mg in test of S. granularis, for S in the spines of A. lixula and the test and spine of S. granularis, for Na in the test of P. lividus and A. lixula and for Cl and Mg/Ca in the test P. lividus. Powder X-ray diffractometry determined that, out of all three species, the spines of P. lividus contained the least Mg, while the test of the same species exhibited higher Mg concentration compared to A. lixula and S. granularis. The current study, although not labeling the specimens attempts to estimate potential time-related elemental differences among other results. These may occur due to changes in abiotic factors, probably water temperature, salinity and/or pH. Divergence in food preference and food availability may also play a key role in possible temporal differences the skeletons of these species

Holocrinid crinoids (Holocrinus) are among the oldest, if not the oldest, post-Paleozoic crinoids, which are widely considered the stem-group isocrinids for the post-Paleozoic monophyletic subclass Articulata. Owing to their phylogenetic and stratigraphic position, the morphology and paleobiology of these crinoids have received considerable attention. Although the holocrinid stalk is similar to that of fossil and living isocrinids, it lacks flat and rigid synostosial articulations, which are sites specialized for autotomy. Holocrinids were thus long considered sessile, without the ability to re-attach. However, taphonomic data, such as specific pattern of preferred disarticulation at the distal facet of nodals, indicated that Holocrinus was likely capable of stalk autotomy and relocation. This trait, that is considered an anti-predatory adaptation against benthic predation, has recently served as example of fundamental change in benthic marine communities, such as the Mesozoic marine revolution (MMR). Here I describe stereom microstructure of the stalk of Early-Middle Triassic Holocrinus. The holocrinid stalk is mainly constructed of straight stereom passageways passing through the columnals, that are diagnostic of long through-going ligaments. At the distal symplexial nodal facet, however, fine and dense stereom, in which pores are irregular in outline and show no alignment, is observed. The latter stereom type strongly resembles synostosial stereom in living isocrinids, that is associated with short ligaments, specifically designed for autotomy. These findings thus strongly support stalk shedding abilities in holocrinids. These results emphasize that microstructural observations, coupled with taphonomic data, may provide more insights into functional inferences than macromorphological data alone.

The spines of echinoids are common palaeontological objects, but rarely supply more than this minimal information, because they are difficult to identify to genus or species. Some taxa, particularly cidaroids, may be named based on the external morphology of their spines, but this is of no assistance when identifying spines in thin section. Yet, the internal complexities of the stereom of the echinoid spine may be unique to a particular species or, at least, genus or family. A scanning electron micrograph (SEM) atlas of the internal structure of the primary spines of 14 of the most common species of regular echinoids from shallow–water environments of the tropical western Atlantic Ocean is presented herein. This demonstrates the stereom structure of the spines of each of these species by reference to multiple images. Plates of SEMs are supplemented by brief descriptions and comparisons. This atlas is intended as a tool that can be applied to diverse aspects of palaeontological and sedimentological studies in thin section.

Spines of the slate pencil sea urchin Heterocentrotus mamillatus Linnaeus, 1758, are in focus of biomimetic research as they feature a “graceful” failure behaviour under uniaxial compression dissipating energy and resisting high loads even after high strain. This study elucidates and quantifies the organization of calcitic trabeculae and pores in large primary spines of the slate pencil urchin H. mamillatus by image analysis from scanning electron microscopy, X-ray micro-computed tomography (µCT) and gravimetry. This study delivers a detailed distribution of porosities within the whole spine and shows that parts of the spines have a much higher porosity then hitherto thought. The central part (medulla) of the high-magnesium calcitic stereom of H. mamillatus spines has a porosity range of 75% to nearly 90%. From this innermost structure, more than 200 radially aligned, but often sinuous trabeculae extend to the spine rim. The structure of this complicated meshwork (radiating layer) is best seen in basal cross sections and was confirmed by µCT scans. The radiating layer has a porosity range from 40–70% and is irregularly separated by the dense growth layers (15–35% porosity). Growth layers were classified in proximal and distal growth layers with numbers ranging within a single animal between 3–14 and 2–7, respectively. These growth layers are characteristic for H. mamillatus spines and play a major role in their remarkable mechanical properties. The porosity of the spine increases from base to tip. Biological and mechanical implications of the variations are discussed.

Uintacrinoids (Uintacrinoidea) are among the most bizarre of all the crinoids. These stratigraphically important Late Cretaceous crinoids are characterized by an atypical large stalkless globular cup without cirriferous centrodorsal and extremely long arms. Owing to this unusual morphology, the mode of life of these crinoids has confused palaeontologists for more than a century. While uintacrinoids have been commonly regarded as pelagic forms, either swimming actively or floating passively by means of a putative buoyancy mechanism, some recent authors have favoured a benthic mode of life. However, evidence supporting a benthic lifestyle hypothesis is still limited. Here we describe the stereom microstructure of Marsupites and Uintacrinus. In Marsupites, thecal plates are typically comprised of coarse to medium, clearly structural, galleried stereom, which alternates with zones of fine and deeply penetrating galleried stereom oriented perpendicular to the plate margins. The latter stereom type corresponds to the external ribbed ornament of the theca, and is indicative of collagenous sutural fibers for binding adjacent plates. In Uintacrinus, thecal plates are almost entirely composed of fine galleried stereom diagnostic for collagenous sutural fibers. In both taxa, a perforate stereom layer, that is known to increase plate strengthening and resistance to abrasion in some Recent echinoderms, is developed most externally, and also produces a characteristic interior growth banding pattern. No skeletal adaptations for maintaining buoyancy, such as skeletal lightening and hollow architecture, that are known to occur in nektonic and pseudoplanktonic crinoids, are observed. Instead, the stereom organization in uintacrinoids closely resembles those observed in Recent benthic crinoids. Our findings thus strongly support a benthic mode of life of uintacrinoids. Their widespread distribution within a short time interval can be best explained by having a very long-term planktonic larval stage as previously hypothesized by some authors.

Intermediate morphologies of a new fossil crinoid shed light on the pathway by which crinoids acquired their distinctive arms. Apomorphies originating deep in echinoderm history among early nonblastozoan pentaradiate echinoderms distinguish Tremadocian (earliest Ordovician) crinoid arms from later taxa. The brachial series is separated from the ambulacra, part of the axial skeleton, by lateral plate fields. Cover plates are arrayed in two tiers, and floor plates expressed podial basins and pores. Later during the Early Ordovician, floor plates contacted and nestled into brachials, then were unexpressed as stereom elements entirely and cover plates were reduced to a single tier. Incorporation of these events into a parsimony analysis supports crinoid origin deep in echinoderm history separate from blastozoans (eocrinoids, ‘cystoids’). Arm morphology is exceptionally well-preserved in the late Tremadocian to early FloianAthenacrinus browerinew genus new species. Character analysis supports a hypothesis that this taxon originated early within in the disparid clade.Athenacrinusn. gen. (in Athenacrinidae new family) is the earliest-known crinoid to express what is commonly referred to as ‘compound’ or ‘biradial’ morphology. This terminology is misleading in that no evidence for implied fusion or fission of radials exists, rather it is suggested that this condition arose through disproportionate growth.UUID:http://zoobank.org/b383e039-3298-4472-a7e3-e81684f87cfe

Multibiological multiscale biomimetic design is a novel bionic idea that involves multi-mechanisms. Porous ceramics with a sea urchin stereom structure on a micrometre scale and a nacre mineral bridge structure on a submicron scale have been fabricated via organic foam impregnation and controlled crystallisation. The microstructure and mechanical properties of biomimetic ceramics are, respectively, characterised using scanning electron microscopy and universal testing machine. Moreover, the porosity, reliability and grain boundary stress of biomimetic ceramics are calculated via Archimedes method, Weibull theory and finite element method, respectively. Results show that the ceramic produced in this work has a porosity of 88.16% and an average pore size of 284.65 μm. Mineral bridges of Al2TiO5 with a thickness of 30–230 nm are widely and randomly distributed in the grain boundary glass phase of Al2O3 and improved the compressive strength (2.32 MPa) and Weibull modulus (7.85) of ceramics by the multi-mechanisms of crack deflection, reducing maximum stress and homogenising stress on the grain boundary. These investigations would be of great value to the design and synthesis of novel biomimetic materials. Keywords: Biomimetic ceramic, Finite element method, Stereom, Mineral bridge, Weibull modulus, Compressive property

10 pages; International audience; The extinct echinoderm clade Stylophora consists of some of the strangest known deuterostomes. Stylophorans are known from complete, fully articulated skeletal remains from the middle Cambrian to the Pennsylvanian, but remain difficult to interpret. Their bizarre morphology, with a single appendage extending from a main body, has spawned vigorous debate over the phylogenetic significance of stylophorans, which were long considered modified but bona fide echinoderms with a feeding appendage. More recent interpretation of this appendage as a posterior “tail-like” structure has literally turned the animal back to front, leading to consideration of stylophorans as ancestral chordates, or as hemichordate-like, early echinoderms. Until now, the data feeding the debate have been restricted to evaluations of skeletal anatomy. Here, we apply novel elemental mapping technologies to describe, for the first time, soft tissue traces in stylophorans in conjunction with skeletal molds. The single stylophoran appendage contains a longitudinal canal with perpendicular, elongate extensions projecting beyond hinged biserial plates. This pattern of soft tissues compares most favorably with the hydrocoel, including a water vascular canal and tube feet found in all typical echinoderms. Presence of both calcite stereom and now, an apparent water vascular system, supports echinoderm and not hemichordate-like affinities.

The skeleton of spines and tests of the species of sea urchins Strongylocentrotus intermedius, Mesocentrotus nudus, Scaphechinus mirabilis, and Echinocardium cordatum from the Sea of Japan is composed of a spongy stereom, consisting of calcite with a high content of magnesium. It was found that the tests and spines of the skeletons of sea urchins are composed of calcium–organic composite materials inlaid with other metals: Mg, Fe, Zn, and Rb. In the four species of sea urchins studied, the strength and other mechanical properties of the tests and spines differ and depend on the chemical composition and structural organization of their components. It was shown that the content of volatile substances correlates with their fragility or elasticity. It is revealed that the chemical composition of the tests of two species of the spherical sea urchins S. intermedius and M. nudus indicates significant differences between these two species of sea urchins.

One of the most profound environmental changes thought to be reflected in chemical composition of numerous geological archives is Mg/Ca ratio of the seawater, which has varied dramatically throughout the Phanerozoic. Echinoderms that today typically form high magnesium calcite skeletons are increasingly being utilized as a proxy for interpreting secular changes in seawater chemistry. However, accurate characterization of the diagenetic changes of their metastable high magnesium calcite skeletons is a prerequisite for assessing their original, major-element geochemical composition. Here we expand the existing models of diagenesis of echinoderm skeleton by integration of various analytical methods that up to now rarely have been used to assess the diagenetic changes of fossil echinoderms. We validated the preservation of a suite of differently preserved echinoderm ossicles, mostly crinoids, ranging in age from the Cambrian through Recent. In 13 of 99 fossil echinoderm ossicles we found well-preserved porous microstructure (stereom), non-luminescent behaviour or blotchy dark color in cathodoluminescence, and distinct nanostructural features (layered and nanocomposite structure). Moreover, in representatives of such preserved samples, distribution of sulphates associated with organic matter is identical to those in Recent echinoderms. Only such ossicles, despite of local micrometer-scale diagenetic changes, were herein considered well-preserved, retaining their original major-element skeletal composition. By contrast, majority of samples show transformation to the stable low magnesium calcite that leads to obliteration of the primary geochemical and micro/nanostructural features and is accompanied with increase in cathodoluminescence emission intensity. Using only well-preserved fossil echinoderm samples, we found purely random variation in Mg/Ca in echinoderm skeletons through the observed time series; any periodicities in echinoderm skeletal Mg/Ca ratio which might be related to the secular transitions in calcite and aragonite seas were not confirmed. These findings suggest that, in contrast to some groups of organisms with relatively weak control over their biomineralization (such as algae, sponges, and bryozoans), in which polymorph mineralogies consistently changed according to the seawater type, application of fossil echinoderms, in particular crinoids, to seawater Mg/Ca reconstructions is unreliable. These data emphasize a key-role of physiological factors (the so-called vital effects) in echinoderm biomineralization.

Anthropogenic CO2 – driven ocean acidification (OA) is causing a decrease in seawater pH and the saturation state of calcium carbonate minerals, compromising the ability of calcifying species to produce and maintain their skeletons. Sea urchins are ecologically important calcifying species and we investigated the impacts of long-term (9 month) exposure to near-future OA (Ambient – pHNBS 8.01; OA – pHNBS 7.6) on the skeleton microstructure of Heliocidaris erythrogramma using scanning electron microscopy (SEM), micro-computed tomography (μCT) and nanoindentation. SEM revealed that the youngest plates (apical plates) which had likely grown in experimental conditions had larger pores in the OA group (pore surface area ~ 72% larger) compared with those of urchins maintained in ambient pH. High-resolution, μCT 3-D reconstructions of the apical plates revealed that the experimental OA treatment urchins had a ~14% greater porosity and ~17% less biomineral, suggesting an inability to finely regulate skeletogenesis. The mid-test ambital plates established prior to this study did not show any OA associated change in porosity. Nanoindentation of the apical plates indicated that OA reduced skeletal hardness and elasticity. Stereom pore size is a key trait of the sea urchin endoskeleton and increased porosity in H. erythrogramma is likely to impact its biological functions as well as its biomechanical capacity to defend against predation and physical disturbances.

Exceptionally well-preserved ossicles of xenomorphic stalked crinoids (Echinodermata) were found into the Late Ypresian clay of the Tuilerie de Gan (Pyrenees-Atlantiques, southwestern France). Three kinds of columnal articulation correspond to three different genera, including the new genus Eocenocrinus. These columnals are attributed to Paraconocrinus romanensis, Democrinus londinensis and Eocenocrinus hessi n. gen., n. sp. Associated benthic fauna as well as columnal characters related to water depth confirm an increasing depth to an epibathyal environment as previously suggested by mollusk and foraminifer associations. Paraconocrinus romanensis associated with Democrinus londinensis mark the maximum water depth, which did not exceed 300 m. Distal columnal series with proximal roots of P. romanensis and D. londinensis were collected with their ossicles connected, indicating that these species lived on a muddy bottom. E. hessi n. gen., n. sp. is suspected to have been attached on hard substrate. Without diagenetic crystallizing, the crinoid stereom and its micro-biocorrosion appear as in extant specimens. We attribute to Eocenocrinus n. gen. large columnals previously described from northeastern Italy and recognize two species: E. bayani n. gen., n. sp. (Middle Lutetian) and E. didymus (Priabonian). E. hessi n. gen., n. sp. may represent the oldest known species in the family Phrynocrinidae.

Recent studies have shown that in some light-sensitive species of an brittlestar (Asteroidea, Echinodermata), the upper surface of the dorsal arm plate bears arrays of hemispherical microstructures which in combination with underlying neural bundles and intraskeletal chromatophores probably function as a compound eye. These calcitic lenses possess superior properties such as light weight, mechanical strength, and very low aberration and birefringence; they display a unique focusing effect, signal enhancement, intensity adjustment, angular selectivity, and photochromic activity. The discovery of these unique optical structures revealed that brittlestar visual system is more sophisticated than initially thought and has inspired active interest toward designing of biomimetic highly tunable optical elements for a wide variety of cutting-edge technological applications. Up to this moment, analogous spherical calcitic lenses have been only reported in a few species of modern brittlestars and starfish. Similar calcitic microlenses have been also observed in the Late Cretaceous fossil echinoderms. Here, we report the structural evidence for the presence of calcitic microlenses in an extant species of starfish Archaster typicus. The close resemblance in microstructure and location between the transparent regions of compact stereom described above and microlenses in the photosensitive brittlestar Ophiocoma wendtii suggests that these regions may be involved with the photoreceptor system in A. typicus.

Background: Fluorochrome staining is among the most widely used techniques to study growth dynamics of echinoderms. However, it fails to detect fine-scale increments because produced marks are commonly diffusely distributed within the skeleton. In this paper we investigated the potential of trace element (manganese) labeling and subsequent cathodoluminescence (CL) imaging in fine-scale growth studies of echinoderms. Results: Three species of sea urchins (Paracentrotus lividus, Echinometra sp. and Prionocidaris baculosa) were incubated for different periods of time in seawater enriched in different Mn2+ concentrations (1mg/L; 3mg/L; 61.6mg/L). Labeling with low Mn2+ concentrations (at 1mg/L and 3mg/L) had no effect on behavior, growth and survival of sea urchins in contrast to the high Mn2+ dosage (at 61.6mg/L) that resulted in lack of skeleton growth. Under CL, manganese produced clearly visible luminescent growth fronts in these specimens (observed in sectioned skeletal parts), which allowed for a determination of the average extension rates and provided direct insights into the morphogenesis of different types of ossicles. The three species tend to follow the same patterns of growth. Spine growth starts with the formation of microspines which are simultaneously becoming reinforced by addition of thickening layers. Spine septa develop via deposition of porous stereom that is rapidly (within less than 2days) filled by secondary calcite. Development of the inner cortex in cidaroids begins with the formation of microspines which grow at ~3.5μm/day. Later on, deposition of the outer polycrystalline cortex with spinules and protuberances proceeds at ~12μm/day. The growth of tooth can be rapid (up to ~1.8mm/day) and starts with the formation of primary plates (pp) in plumula. Later on, during the further growth of pp in aboral and lateral directions, secondary extensions develop inside (in chronological order: lamellae, needles, secondary plate, prisms and carinar processes), which are increasingly being solidified towards the incisal end. Interradial growth in the ambital interambulacral test plates exceeds meridional growth and inner thickening. Conclusions: Mn2+ labeling coupled with CL imaging is a promising, low-cost and easily applicable method to study growth dynamics of echinoderms at the micro-length scale. The method allowed us to evaluate and refine models of echinoid skeleton morphogenesis., SCOPUS: ar.j, info:eu-repo/semantics/published

A new species of Apiocrinites is described from the Matmor Formation (Middle Jurassic, upper Callovian) of Hamakhtesh Hagadol, southern Israel. Apiocrinites feldmani n. sp. is a small species associated with the larger A. negevensis in a calcareous sponge and coral patch reef community. During life the columns of A. feldmani were commonly and preferentially infested with a soft-bodied parasite that grew with the crinoid and became embedded in its skeleton. These parasites embedded at the articulation between columnals, forcing the columnals to grow around them and producing with time a conical pit surrounded by swollen stereom. If the parasite died while the crinoid was still growing, the conical pit was roofed over by continued growth of columnals, resulting in a swelling with no external opening. Because the crinoids invested energy in forming extra skeleton around these parasites and because the crinoid stems were consequently deformed and likely lost flexibility, we consider these parasites to have caused significant harm. Curiously, these parasites apparently did not infect the larger and more common contemporaneous A. negevensis that lived in the same community.

Ocean acidification, a process caused by the continuous rise of atmospheric CO2 levels, is expected to have a profound impact on marine invertebrates. Findings of the numerous studies conducted in this field indicate high variability in species responses to future ocean conditions. This study aimed at understanding the effects of long-term exposure to elevated pCO2 conditions on the performance of adult Echinometra sp. EE from the Gulf of Aqaba (Red Sea). During an 11-month incubation under high pCO2 (1,433 μatm, pHNBS 7.7) and control (435 μatm, pHNBS 8.1) conditions, we examined the urchins’ somatic and gonadal growth, gametogenesis and skeletal microstructure. Somatic and gonadal growths were exhibited with no significant differences between the treatments. In addition, all urchins in the experiment completed a full reproductive cycle, typical of natural populations, with no detectable impact of increased pCO2 on the timing, duration or progression of the cycle. Furthermore, scanning electron microscopy imaging of urchin tests and spines revealed no signs of the usual observed effects of acidosis, such as skeletal dissolution, widened stereom pores or non-smoothed structures. Our results, which yielded no significant impact of the high pCO2 treatment on any of the examined processes in the urchins studied, suggest high resistance of adult Echinometra sp. EE to near future ocean acidification conditions. With respect to other findings in this area, the outcome of this study provides an example of the complicated and diverse responses of echinoids to the predicted environmental changes.

The material for the present paper is based on 50 kg of processed sediment from the Early Kimmeridgian of Geisingen. The most frequent crinoids comprise cups and brachials of the roveacrinid Saccocoma quenstedti while Crassicoma feifeli is represented by a few cups only; these remains are not described. Cups and primibrachials of Eugeniacrinites cariophilites are the commonest cyrtocrinids, while cups of Pilocrinus moussoni are rather rare and not further treated, as are columnals of the two species. The ontogenetic series of cups and axillary primibrachials of E. cariophilites starts from ossicles of about 0.5 mm in height; and growth is allometric in both types. Postlarval cups resemble phyllocrinids; the distinctive shape with lanceolate interradial extensions and wide articular facets appears at a later stage. The spearhead-shaped axillary primibrachials are synapomorphic. The youngest of these ossicles with a muscular facet proximally were able to form a flat roof over the radial cavity. First primibrachials with synostosial distal facet appeared at a slightly later stage with a width of 1 mm; growth is isometric. A significant number of cups are mutilated by bite marks. The predatory attacks were sublethal in most cases as shown by secondary stereom growth and regenerated facets. First primibrachials are not deformed, but deformations occur in a small number of second primibrachials. The results suggest that the predators, presumably fishes, targeted the soft parts in the cup. Enigmatic brachials with a large wing to one side and a facet to an arm are thought to belong to E. cariophilites and presumably attached to deformed cups; the wings may have been an antipredatory adaptation providing some shelter to the cup. The various antipredator morphologies in cyrtocrinid history are discussed. The presently available growth series of Eugeniacrinites invites discussion of early cyrtocrinid phylogeny. Eugeniacrinites seems to have been derived from Phyllocrinidae; and Sclerocrinidae with Cyrtocrinus as the first representative in the Middle Jurassic is thought to have originated from Early Jurassic Tetracrinidae such as Bilecicrinus.

Cidaroid sea urchins are the sister clade to all other extant echinoids and have numerous unique features, including unusual primary spines. These lack an epidermis when mature, exposing their high-magnesium calcite skeleton to seawater and allowing the settlement of numerous epibionts. Cidaroid spines are made of an inner core of classical monocrystalline skeleton and an outer layer of polycrystalline magnesium calcite. Interestingly, cidaroids survived the Permian-Triassic crisis, which was characterized by severe acidification of the ocean. Currently, numerous members of this group inhabit the deep ocean, below the saturation horizon for their magnesium calcite skeleton. This suggests that members of this taxon may have characteristics that may allow them to resist ongoing ocean acidification linked to global change. We compared the effect of acidified seawater (pH 7.2, 7.6, or 8.2) on mature spines with a fully developed cortex to that on young, growing spines, in which only the stereom core was developed. The cortex of mature spines was much more resistant to etching than the stereom of young spines. We then examined the properties of the cortex that might be responsible for its resistance compared to the underlying stereomic layers, namely morphology, intramineral organic material, magnesium concentration, intrinsic solubility of the mineral, and density. Our results indicate that the acidification resistance of the cortex is probably due to its lower magnesium concentration and higher density, the latter reducing the amount of surface area in contact with acidified seawater. The biofilm and epibionts covering the cortex of mature spines may also reduce its exposure to seawater. © 2014, The American Microscopical Society, Inc.