Irregular Echinoids Research Articles

Late Holocene echinoderm assemblages can serve as paleoenvironmental tracers in an Antarctic fjord

High Latitude fjords can serve as sediment trap, bearing different type of proxies, from geochemical to micropaleontological ones, making them exceptional tools for paleoenvironmental reconstruction. However, some unconventional proxies can be present and can be used to depict a comprehensive and exhaustive interpretation of past changes. Here, studying a sediment core in Edisto Inlet (Ross Sea, Antarctica) we used irregular echinoid spines and ophiuroids (Ophionotus victoriae) ossicles to trace environmental changes throughout the last 3.6 kyrs BP. Irregular echinoids can serve as proxy for the organic matter content, while O. victoriae ossicles can be used as proxy for steady sea-ice cycle along with organic deposition events. O. victoriae release a high number of ossicles, making estimation about the population quite challenging; still, presence data, can be easily collected. By applying Generative Additive Models to the stratigraphical distribution of these data, we detected an environmental phase that was previously unnoticed by other traditional proxies: the Ophiuroid Optimum (2–1.5 kyrs BP). In conclusion, here we demonstrate how echinoderm presence can be used as a valuable source of information, while proving the potential of modelling binary data to detect long-term trend in Holocene stratigraphical records.

Taxonomy and significance of Cenomanian echinoids distribution in the Batna Mounts (NE, Algeria)

From 700 echinoids specimens collected from the Cenomanian sediments of Batna Mounts, 16 species (9 regular and 7 irregular) belonging to 11 genera, 10 families and 7 orders, have been identified. One species is reported for the first time from Algeria Pygaulus subaequalis. The irregular echinoids, including the Hemiasteridae remain the most abundant. The abundance, biodiversity and distribution of the echinoids in the Cenomanian deposits leads to recognize echinoid assemblages or echinoid biozones closely related to sea level variation. The identified echinoid biozones are as the following (1) a lower Cenomanian association representing the Hemiaster gabrielis Total Range Zone (Association A) characterizing a relatively deep environment, located distally in the platform; (2) a middle Cenomanian association which comprises the Mecaster aumalensis - M. pseudofourneli Assemblage Zone (Association B) representing a shallower marine environment; (3) two associations in the upper Cenomanian Mecaster batnensis Acme Zone (Association C1) and the first occurrence of the holectypoids (Association C2) which indicates slight bathymetric fluctuation between the lower and upper infralittoral zones; (4) towards the terminalCenomanian, the Mecaster cf. heberti Total Range Zone (Association D), corresponds to a shallow subreefal environment.

Using the Discontinuous Bi-viscosity model to analyze the three-dimensional flow field and local scour behavior around the Claviaster libycus

Abstract Previous studies have suggested that irregular echinoids exhibit higher survival rates than regular echinoids following mass extinctions. This study focuses on the irregular echinoid Claviaster libycus, investigating its flow field and scour behavior under extreme water flow conditions through numerical simulations and experiments. The numerical model Splash3D used in this study was modified from the open-source code Truchas developed by the U.S. National Laboratory. Splash3D solves the three-dimensional incompressible Navier-Stokes Eqs.. The fluid volume method describes the water surface kinematics and sand surface kinematics. Since Claviaster libycus is semi-submerged in the sand, a discontinuous bi-viscosity model describes the rheological behavior of the bed material. The research findings indicate that when the gonopore of Claviaster libycus faces downstream, there is no evident horseshoe vortex flow, which contributes to reducing the occurrence of localized scour. This also validates the hypothesis of this study: the transition of echinoids from pentaradial symmetry to bilateral symmetry assists in stabilizing bottom sediments and reducing localized scour.

The El Mizab formation (Talerhza Basin, north-west Morocco): Albian–early Cenomanian faunal diversity and paleoenvironment

The Talerhza Basin is a small basin in north-west Morocco, in which the Albian–lower Cenomanian succession consists of three formations; in ascending order, the El Heifouf, Bab Lkarma and El Mizab formations. The first two units, of early–middle Albian age, comprise sandy marlstones and sandy limestones, respectively, and yield rare gastropods. The El Mizab Formation consists of an alternation of marlstones and argillaceous limestones and is richest in macrofauna, being divided into five informal members. The first member (silty marly limestone) is rich in small-sized debris of oyster shells and also yields gastropods and irregular echinoids; the second (lower shelly marly limestone) and the fourth (upper shelly marly limestone) members are rich in bivalves and contain, mainly the second member, gastropods, irregular echinoids and ammonites of late Albian age, representing the Mortoniceras pricei, Mortoniceras inflatum and Mortoniceras fallax zones; the third member (platy chalky limestone) is barren of macrofauna; the fifth one (marly limestone with Rhynchostreon), of early Cenomanian age, is rich in a monospecific bivalve, Rhynchostreon suborbiculatum. Twenty-eight species of bivalves, three irregular echinoids, ten gastropods and nine ammonites have been identified. The spatial distribution of bivalve faunas through the Cretaceous basin shows that some of these taxa were extremely abundant; mainly Lopha syphax in the upper Albian and Rhynchostreon suborbiculatum in the lower Cenomanian deposits. Most of the studied groups of macrofauna are common to several Cretaceous epicontinental basins of northern Gondwana, western and eastern margins of the Atlantic Ocean and the Cretaceous trans-Saharan marine corridor.

Diversity patterns of echinoids (Echinodermata: Echinoidea) in shallow waters of the Mexican Pacific

The Mexican Pacific hosts a large diversity of echinoids occupying different habitats and ecological niches; nevertheless, the group remains scarcely studied in terms of their spatial patterns of biodiversity and variation in the region. This work evaluated the alpha, beta, and gamma diversity of echinoids living in the Mexican Pacific's shallow waters (0–200 m) at three spatial scales: Operational geographic units (OGUs), ecoregions, and provinces. Alpha diversity was evaluated through the standardized coverage values of 0D, 1D, and 2D, while the contribution of alpha and beta diversity components to gamma diversity was estimated with additive partitioning. Finally, we evaluated whether beta diversity resulted from overlap, species replacement, or richness differences. A total of 45 species and 2,232 incidences were registered in the 150 OGUs distributed throughout the Mexican Pacific. Cluster completeness in the ecoregions of the Warm Temperate Northeast Pacific (WTNP) province was higher (> 95 %) than in the ecoregions of the Eastern Tropical Pacific (TEaP) province. Standardized coverage values of the 0D, 1D, and 2D indices showed differences between the ecoregions Cortezian and Magdalena Transition in the WTNP province. At the ecoregion and province level, alpha diversity might be influenced by sampling techniques and habitat availability, which limits the distribution of regular and irregular echinoids. Gamma diversity is mainly determined by beta diversity at the ecoregion scale, where species overlap and richness differences were the major contributing components, probably resulting from substrate dependence, habitat availability, and mesoscale ocean circulation patterns.

A micromorphological analysis ofBolonia lataMeunier from the Cretaceous of the Neuquén Basin (Patagonia, Argentina): new insights into the tracemaker

AbstractPolychaetes, echinoids and gastropods have been proposed as tracemakers forBoloniaMeunier, an elongate positive epirelief trace fossil characterized by two lobes composed of biserial, subtriangular pads and a mostly heart‐shaped cross‐section. Here, the internal structure and micromorphology ofBoloniaare described for the first time using serial thin sections from shallow‐marine Lower Cretaceous intervals of the Agrio Formation (Neuquén Basin, Argentina). In vertical thin sections, a conical structure of variable width extends centrally from the base to the top of the trace. In horizontal thin sections, grains are reoriented and reworked, forming a central zigzag structure. The organic matter and clays form grain aggregates representing the internal structure of individual pads of the trace fossil. The sediment has mostly been reoriented, with grains making up subcircular pods. We interpret the central conical structure as the collapse of the medial zone of the trace fossil, which could have destroyed drain tubes, especially in the absence of early cementation. Studying horizontal thin sections, we reconstruct the diagnostic biserial pads as biserial concave structures. These are interpreted as backfilling structures produced by the aboral and lateral spines of irregular echinoids, which worked together to compact the sediment anteroposteriorly and moved alternatively, explaining the zigzag pattern in the menisci. We propose Spatangoidea or Cassiduloidea (or a closely related group) with a similar burrowing ability and spine movement as tracemakers of theseBoloniaspecimens.

Spatial distribution, diversity, and taphonomy of clypeasteroid and spatangoid echinoids of the central Florida Keys.

Irregular echinoids are ecosystem engineers with diverse functional services. Documenting present-day distribution of those widespread organisms is important for understanding their ecological significance and enhancing our ability to interpret their rich fossil record. This study summarizes SCUBA surveys of clypeasteroid and spatangoid echinoids conducted in 2020 and 2021 along the central part of the Florida Keys. The survey included observations on both live and dead specimens, their distribution, habitat preferences, abundance, and live-dead comparison. Echinoids were found at 17 out of 27 examined sites (63%) and occurred across a wide range of habitats including coastal seagrass meadows, subtidal sand and seagrass settings of the Hawk Channel, backreef sands, and fine muddy sands of deeper forereef habitats. The encountered species, both dead and alive, included Clypeaster rosaceus (four sites), Clypeaster subdepressus (five sites), Encope michelini (three sites), Leodia sexiesperforata (eight sites), Meoma ventricosa (nine sites), and Plagiobrissus grandis (four sites). All sites were dominated by one species, but some sites included up to five echinoid species. Live-dead fidelity was high, including a good agreement in species composition of living and dead assemblages, congruence in species rank abundance, and overlapping spatial distribution patterns. This high fidelity may either reflect long-term persistence of local echinoid populations or fragility of echinoid tests that could prevent post-mortem transport and the formation of time-averaged death assemblages. Regardless of causative factors, the live-dead comparisons suggest that irregular echinoid assemblages, from settings that are comparable to the study area, may provide a fossil record with a high spatial and compositional fidelity. The survey of live fauna is consistent with past regional surveys in terms of identity of observed species, their rank abundance, and their spatial distribution patterns. The results suggest that despite increasingly frequent hurricanes, active seasonal fisheries, massive tourism, and urban development, irregular echinoids continue to thrive across a wide range of habitats where they provide diverse ecosystem services by oxygenating sediments, recycling organic matter, supporting commensal organisms, and providing food to predators. Results reported here document the present-day status of local echinoid populations and should serve as a useful reference point for assessing future regional changes in echinoid distribution and abundance.

Feeding in spatangoids: the case of Abatus Cordatus in the Kerguelen Islands (Southern Ocean)

Irregular urchins exclusively live in marine soft bottom habitats, dwelling either upon or inside sediments and selectively picking up sediment grains and organic particles, or swallowing bulk sediment to feed on the associated organic matter. The exact food source and dietary requirements of most irregular echinoids, however, remain incompletely understood. The schizasterid species Abatus cordatus (Verrill, 1876) is a sub-Antarctic spatangoid that is endemic to the Kerguelen. The feeding behaviour of A. cordatus was investigated using simultaneously metabarcoding and stable isotope approaches. Comparison of ingested and surrounding sediments by metabarcoding revealed a limited selective ingestion of prokaryotes and eukaryotes by the urchin. Compared to surrounding sediments, the gut content had (i) higher carbon and nitrogen concentrations potentially due to selective ingestion of organic matter and/or the sea urchin mucus secretion and (ii) δ15N enrichment due to the selective assimilation of lighter isotope in the gut. Feeding experiments were performed using 13C and 15 N-enriched sediments in aquariums. The progression of stable isotope enrichment in proximal and distal parts of the digestive track of A. cordatus revealed that all particles are not similarly transported likely due to siphon functioning. Ingestion of water with associated dissolved and particulate organic matter should play an important role in urchin nutrition. A. cordatus had a gut resident time fluctuating between 76 and 101 h and an ingestion rate of 36 mg dry sediment h−1 suggesting that dense populations of the species may play a key ecological role through bioturbation in soft bottom shallow-water habitats of the Kerguelen Islands.

Miocene Rocks Around the Marádah Oasis, Central Sirt Basin, Libya: Facies Development and Implication on Stratigraphy

The Miocene rocks of the Marádah Formation have been stratigraphically investigated from four stratigraphical sections around the Marádah Oasis in the Central Sirt Basin of Libya. The field investigations led to the identification of two members, the lower Qarat Jahannam Member and the upper Ar Ráhlah Member. Fourteen sedimentary facies at the outcrop-scale representing a gradual development of sedimentation from a continental clastic witness in the southwestern outcrops to transitional estuarine, lagoonal, and beaches to the proximal offshore in the northern outcrops, were recognized. The results indicates that the accumulation of the Marádah Formation is transgressive in nature and corresponding to two phases of deposition which have been mentioned in the earlier studies.
 
 The first phase is continental-dominated facies in which cross-bedded sandstones and calcareous sands comprise most of the depositional sequence of the lower Qarat Jahannam Member at the southwestern outcrops. This phase, however, is characterized by extremely bioturbated laminated-shale conquered by Skolithos ichnofacies in the lower part of the upper Ar Ráhlah Member at the northern outcrops. This phase is providing further evidence that the contact between the two members is diachronous everywhere in the study area. The clastic-phase has thought to be deposited in the Lower Miocene (Aquitanian-Burdigalian) since the lower Qarat Jahannam Member rests on an erosional surface of submarine origin in the southwestern outcrops above a 0.5 m. thick of a nummulitic unit of the Oligocene Bu Hashish Formation.
 
 The second phase is marine-dominated facies in which a bioclastic limestone unit rich in thick and disarticulated oysters, including Crassostrea gryphoides (Schlottheim), characterizes the sediments of the Ar Ráhlah Member at the southwestern outcrops. This phase also includes the upper part of the latter member at the northern outcrops in which a detrital limestone unit rich in turritelline gastropods is overlying by thick-bedded calcarenites rich in disarticulated oysters, gastropods, irregular echinoids (notably, Clypeaster and Echinolampas), bryozoans, and celestite corals. The upper part of the Ar Ráhlah Member at the northern outcrops, nevertheless, is terminated by a quite hard dolomitic limestone and by a pretty soft dolomitic marly limestone. Both lithologies, however, are combined with medium-sized oysters, including Ostrea digitalina Fuchs, and pectinid bivalves. The second phase, however, is interpreted to be deposited in the Middle Miocene (Langhian and Serravallian) based on the total-stratigraphic range of the larger benthic foraminifera Borelis melo melo (Fichtel & Moll), which recovered from the studied washed residues, and the associated microfacies.

Benthic invertebrate communities as a function of sea-level fluctuations and hydrodynamics: A case from the Cenomanian-Turonian of Wadi Tarfa (Eastern Desert, Egypt)

Understanding the response of the benthic invertebrates to long-term sea-level changes, which is possible only from the fossil record, is crucial for conservation biology. Based on integrated sedimentological and biostratigraphical data from the Cenomanian-Turonian succession of Wadi Tarfa (Eastern Desert, Egypt), a cyclic pattern, comparable to those of 2nd order sequence stratigraphy, between the community structure of the invertebrates and the sea-level fluctuations was revealed. Quantitative analysis of 1756 specimens representing 154 invertebrate genera encompassing mollusks and echinoid revealed that invertebrate communities can be classified into three different types. The first associated with the initiation of transgression (TST) and dominated mainly by opportunistic, epifaunal suspension-feeders, including gastropods and bivalves. This community is characterized by lower diversity values. The second community belonged to the maximum flooding zone (MFZ) and mainly dominated by infaunal deposit-feeders of irregular echinoids and bivalves and characterized by higher diversity. The last community is less diverse, dominated by few epifaunal-suspension feeders and occupying the late highstand system tract (HST). The lower diversity values during the early TST/late HST may result from the persistence of waves/the higher sedimentation rates. Consequently, only opportunistic taxa flourished. In contrast, diversity increases with flooding and is at a maximum and dominance at a minimum at the transgression peak (MFZ). Here, the high diversity, which is commonly augmented by time-averaging, most likely contributed also to the environmental stability, which increases with flooding. Accumulation of biogenic hardparts in combination with low rates of sedimentation may increase substrate heterogeneity and thus increases beta diversity (niche differentiation). The cyclic pattern of the community attributes results from the hydrodynamic setting accompanying the sea-level changes. The role of ecoenvironmental and taphonomic mechanisms in shell concentrations are also discussed.

To see or to smell: the role of vision in host-recognition by an ectoparasitic crab

Crustaceans are associated with a wide diversity of hosts, using both chemical and visual cues to recognize them. The pea crab Dissodactylus primitivus is an ectoparasite of two species of irregular echinoids living in the Caribbean Sea. Previous studies showed that the crab chemically discriminates its hosts from non-host species. The possibility that the parasite also visually localizes its host was investigated here through behavioral and morphological approaches. The responses of the parasite to visual cues were investigated in aquaria and show a limited visual ability, leading to sheltering rather than to host localization. This suggests that visual cues are not required to maintain the specificity of the parasitism. Microscopical investigations corroborate this conclusion by revealing a pair of small compound eyes mainly localized under the cephalothorax. The ommatidia (facets) were only found on the covered surface (below the cuticle). Interestingly, a lot of setae were observed around or even directly on the eye and might participate in the overall chemical detection.

<p class="HeadingRunIn"><strong>A geometric morphometric analysis of <em>Arachnoides</em> <em>placenta</em> (Echinoidea: Clypeasteroida): An examination of ontogenetic development and morphological variation</strong></p>

Irregular echinoids, particularly clypeasteroids or “sand dollars”, have obtained highly adaptive morphologies suited to their life habitats. Specimens (n = 26) of a clypeasteroid echinoid Arachnoides placenta were examined to understand how these adaptive morphologies were ontogenetically and developmentally obtained. Ontogenetically, early post-larval juvenile specimens have a pentagonal morphologic outline (known as ambitus) that shifts to a circular or a sub-circular morphology observed in the largest adult specimens. Circular morphology appears optimized for the adult life habitat or niche. Both landmark and semilandmark geometric morphometric methodologies were applied to quantify shape change, ontogenetic variation, and developmental morphology in A. placenta. Ambitus change is concentrated along the interambulacral regions with broader curvature variations occurring across both ambulacral and interambulacral regions. Circular adult morphology was a result of non-isometric shape change concentrated anteriorly with minor variation around posterior margin/periproctal furrow. Interior morphologic change of the petaloids and periproct was also quantified, mainly impacting posterior outline morphology. Minimal deformation of the basicoronal plates was detected, indicating stability during ontogeny. Results indicated that complex, non-isometric allometric shape change, both along the ambitus and interiorly, is required to morph from a pentagonal outline in post-larval juveniles to a circular or sub-circular ambitus morphology in adults. This analysis demonstrates the advantages of both landmark and semilandmark geometric morphometric analyses for quantifying developmental change and shape variation in Clypeasteroida.

Paleoecology of sublittoral Miocene echinoids from Sardinia: A case study for substrate controls of faunal distributions

AbstractA rich echinoid fauna within the middle Miocene carbonate sedimentary succession cropping out along the coast between Santa Caterina di Pittinuri and S'Archittu (central-western Sardinia) allows the comparison of faunal gradients and preservation potentials from both hard and soft substrata. Three echinoid assemblages are recognized. Faunal composition, as well as taphonomic and sedimentological features and functional morphological interpretation of the echinoid test indicate an outer sublittoral setting. Assemblage 1 represents a highly structured environment within the photic zone, with mobile substrata occupied by infaunal irregular echinoids, mainly spatangoids, and localized hard substrata, provided by rhodolith beds, with epibenthic regular echinoids represented by the co-occurrence of the diadematidDiademaGray, 1825 and the toxopneustidsTripneustesL. Agassiz, 1841 andSchizechinusPomel, 1869. Assemblage 2 shows a higher diversity of irregular echinoids, dominated by the clypeasteroidsEchinocyamusvan Phelsum, 1774 andClypeasterLamarck, 1801 and different spatangoids, with the minute trigonocidaridGenocidarisA. Agassiz, 1869 among regular echinoids. This assemblage points to a soft-bottom environment with moderate water-energy conditions, periodically affected by storms. A low-diversity echinoid fauna in Assemblage 3, dominated by the spatangoidsBrissopsisL. Agassiz, 1840 andOvaGray, 1825, documents a deeper, soft-bottom environment, possibly below storm-wave base. These results indicate that the diversity of echinoid faunas originating in sublittoral environments is related to: (1) the presence of both soft and hard substrata, (2) differential preservation potentials of the various echinoid taxa, (3) intense bioturbation, and (4) sediment deposition by sporadic storm events.

Taxonomy and distribution of irregular echinoids (Echinoidea: Irregularia) from Sri Lanka.

The earliest information on Sri Lankan echinoid species belonging to the Irregularia dates back to Alexander Agassiz (1872). However, the current knowledge of diversity and distribution of irregular echinoids from Sri Lanka (formerly Ceylon) remains sparse. In addition, there are no recent taxonomic studies or biodiversity surveys for irregular echinoids, and no illustrated field-guides or reference collections are available specifically for Sri Lanka. To address these gaps, left open for more than 100 years since the work of Clark (1915), this study was conducted as an island-wide systematic sampling survey. Over 200 echinoid specimens were collected from 24 localities in Sri Lankan coastal waters by snorkelling and SCUBA diving down to 33 m depth. The collected specimens were identified using existing keys and authenticated with specimens available at the Natural History Museum in Vienna, Austria. The present study records 22 irregular echinoid species belonging to 15 genera and nine families in four orders. Among the identified irregular echinoids, six species, Echinocyamus megapetalus H.L. Clark, 1914, Fibularia ovulum Lamarck, 1816, Fibulariella angulipora Mortensen, 1948, Echinodiscus cf. truncatus L. Agassiz, 1841, Peronella oblonga Mortensen, 1948 and Brissus cf. agassizii Döderlein, 1885, are new records for Sri Lanka. Four unidentified, possibly new species belonging to the genera Fibularia, Jacksonaster and Metalia are reported, but kept in open nomenclature until more material becomes available. At present, the diversity of irregular echinoids from Sri Lanka now stands at 37 species representing 11 families in four orders. A dichotomous key is presented for all Sri Lankan irregular echinoids.

Colony growth strategies, dormancy and repair in some Late Cretaceous encrusting bryozoans: insights into the ecology of the Chalk seabed

Bryozoans are among the most common macrofossils in the Late Cretaceous Chalk. They include many species that encrusted hard substrates, notably echinoid tests, forming habitat islands on the Chalk seabed. The growth strategies adopted by these bryozoans, as well as the occurrence of reparative structures, provides evidence of the conditions experienced by bryozoans and other benthic animals during the accumulation of this unique pelagic sediment deposited over large areas of the continental shelf. Here, we use historical material in the Natural History Museum, London, to provide qualitative evidence that whereas available substrates, including irregular echinoids, were long-lasting, most individual bryozoan colonies were probably short-lived. Some cheilostome species produced heavily calcified polymorphic zooids at the outer edges of the colony that persisted after loss of the feeding autozooids and became the source of regenerative colony growth. Short-term (possibly annual) periodicity is suggested in the benthic environment experienced by encrusting bryozoans, which may have possibly been a result of cyclical variations in dinoflagellate food supply and/or swamping by unpalatable and potentially poisonous coccolithospheres.

Riqueza y distribución de equinoideos irregulares (Echinoidea: Cassiduloida, Clypeasteroida, Holasteroida y Spatangoida) del Pacífico central mexicano

Background. The diversity of irregular echinoids along the Pacific coast of Mexico is still not well known. This group has developed a selection of a restricted substrate; in addition, they are morphologically adapted to bury themselves in sediment that makes them difficult to locate in the field. Goals. To prepare a checklist of species of irregular echinoids including new records of the Cassiduloida, Clypeasteroida, Holasteroida, and Spatangoida orders found along the coasts of Nayarit, Jalisco, and Colima. Methods. Organisms were collected through various sampling operations undertaken between December 2013 and August 2017, in subtidal zones with Scuba diving gear (up to 10 m) and in sandy beaches using manual collection. In addition, we carried out a review of bibliographic sources and scientific collections. Results. Eighteen species from nine families and four orders of irregular urchins were registered for the coasts of Nayarit, Jalisco, and Colima. For Nayarit there are nine species and the species Encope micropora was registered for the first time in Playa Novillero. Ten species were recorded in Jalisco and 14 species in Colima, which for both states established new records for the species Rhyncholampas pacificus, Agassizia scrobiculata, Brissus obesus, Metalia spatagus, and Plagiobrissus pacificus. Conclusions. The literature review, complemented with field sampling, helped increase the diversity of species of irregular sea urchins in the central Mexican Pacific region. Determining the diversity of these species will make it possible to propose future studies on their ecology, in order to specify their ecological role in coastal ecosystems and their potential use for the conservation of marine communities.

Diversification rates indicate an early role of adaptive radiations at the origin of modern echinoid fauna.

Evolutionary radiations are fascinating phenomena corresponding to a dramatic diversification of taxa and a burst of cladogenesis over short periods of time. Most evolutionary radiations have long been regarded as adaptive but this has seldom been demonstrated with large-scale comparative datasets including fossil data. Originating in the Early Jurassic, irregular echinoids are emblematic of the spectacular diversification of mobile marine faunas during the Mesozoic Marine Revolution. They diversified as they colonized various habitats, and now constitute the main component of echinoid fauna in modern seas. The evolutionary radiation of irregular echinoids has long been considered as adaptive but this hypothesis has never been tested. In the present work we analyze the evolution of echinoid species richness and morphological disparity over 37 million years based on an extensive fossil dataset. Our results demonstrate that morphological and functional diversifications in certain clades of irregular echinoids were exceptionally high compared to other clades and that they were associated with the evolution of new modes of life and so can be defined as adaptive radiations. The role played by ecological opportunities in the diversification of these clades was critical, with the evolution of the infaunal mode of life promoting the adaptive radiation of irregular echinoids.

Equinoideos irregulares (Orden Spatangoida) del Cretácico de México

Irregular echinoids (Order Spatangoida) from the Cretaceous of Mexico. Echinoids are a very important part of the Mesozoic and Cenozoic fossil fauna of Mexico. Among them, spatangoids are widely represented in several Cretaceous fossiliferous outcrops, and have stratigraphical and paleoecological value due to their good preservation of the Cretaceous. The review of order Spatangoida L. Agassiz, 1840 from the Cretaceous in Mexico allowed un update the taxonomy of species and contributed to the study of paleogeographic and stratigraphic distribution. The order Spatangoida is the most diverse in Mexico with three families (Toxasteridae, Hemiasteridae, Micrasteridae), seven genera (Epiaster, Heteraster, Macraster, Washitaster, Hemiaster, Proraster, Micraster) and 21 species. Family Toxasteridae is the most numerous with 54 % of the species reported for the Cretaceous of Mexico. Spatangoids from the Cretaceous of Mexico are found in different localities in Sonora (Cerro de las Conchas), Chihuahua (Cerro de Muleros, Sierra de Juárez, Placer de Guadalupe, Sierras La Ranchera, El Presidio, Sierra Banco de Lucero, Sierra La Encantada, Villa Ahumada), Coahuila (Sierra de Tlahualilo), Nuevo León (Sinclinal de Delgado), San Luis Potosí (Zamachihue), Colima (El Rosario), Puebla (San Juan Raya, Barranca Salitrillo), Guerrero (Cerro de Ahuexotitlán) and Oaxaca (Las Huertas). Rev. Biol. Trop. 65(Suppl. 1): S113-S136. Epub 2017 November 01.

Diversidad, patrones de distribución y “hotspots” de los equinoideos irregulares (Echinoidea: Irregularia) de México

Diversity, distribution patterns and hotspots of the irregular equinoids (Echinoidea: Irregularia) of Mexico.Irregular echinoids can be found in almost all marine habitats, from the polar to the equatorial regions, and from the intertidal zone to great depths; some species have a cosmopolitan distribution, but most are geographically restricted, and all live in very particular habitats to a greater or lesser degree in Mexico has 153 species distributed within the coastal limits. Geographic barriers (terrestrial barriers and large ocean basins) and ocean current patterns act as primary modulators of the distribution of echinoids; however, there are factors that define the local distribution. The purpose of this work is to analyze the diversity of irregular echinoids in Mexico, as well as to explain the patterns of distribution and to explore the hotspots through panbiogeography as units of high richness. The study area covers all the territorial waters of Mexico in the Pacific Ocean, Atlantic and Caribbean Sea. To obtain the geographical coordinates we used the distribution data of 68 species of irregular echinoids recorded at different depths. We reviewed the specimens deposited in five scientific collections, in addition to the revision of other records from online databases: 1. National Collection of Echinoderms “Ma. Elena Caso Muñoz” of the Instituto de Ciencias del Mar y Limnología (ICML), of the Universidad Nacional Autónoma de México (UNAM); 2. Regional Collection of Invertebrates of the Academic Unit Mazatlán, ICML, UNAM. 3. Invertebrate Zoology Collection, Smithsonian Museum of Natural History, Washington, D.C., United States of America, (USA); 4. Invertebrate Collection, Museum of Comparative Zoology, University of Harvard, Boston, Massachusetts; 5. Invertebrate Zoology, Peabody Museum, Yale University, New Haven, Connecticut; National Information System on Biodiversity (SNIB-CONABIO) and Global Biodiversity Information (GBIF). The generalized tracks were performed by the analysis of endemicity based on the optimization method, using the NDM/VNDM program with a 2° x 2° latitude/longitude grid. Hotspots were obtained by overlapping the generalized tracks using the ArcView program. The best represented was family Brissidae, with 15 species, most of them belonging to the genus Brissopsis, followed by the family Mellitidae (with 12 species), half of them belongs to the genus Encope. The families of irregular sea urchins with a smaller number of species were: Echinoneidae, Plexechinidae, Palaeotropidae and Paleopneustidae, each represented by a single species. The following general patterns of distribution were recognized: 1) groups of widely distributed species and 2) restricted species living in the first few meters of depth (0-20m). Nine consensus areas or generalized tracks were obtained in the Endemicity Analysis and 47 hotspots were recognized. Three areas with high specific wealth were obtained: West Coast of the Gulf of Mexico, Bank of Campeche/Mexican Caribbean and Gulf of California. The Gulf of California area has the highest diversity of irregular echinoids. This is the first approximation in the study of the panbiogeography of echinoderms of Mexico. Rev. Biol. Trop. 65(Suppl. 1): S42-S59. Epub 2017 November 01.

Abyssal foraminifera as the main source of rare and new polyunsaturated fatty acids in deep-sea ecosystems

Many rare and new polyunsaturated fatty acids (FAs) have been found in lipids of the foraminifera Reophax nodulosus, Crithionina sp. and Pyrgo sp. from the abyssal zone of the Kuril Basin (Sea of Okhotsk) and the adjacent abyssal area of Pacific Ocean, including the slope of Kuril-Kamchatka Trench. Polyunsaturated fatty acids (PUFAs) of the (n-5) family, previously unknown for marine organisms, dominated among PUFAs of the agglutinated foraminifera Reophax nodulosus. Moreover, 22:5(n-5) is the main FA of these foraminifera: its content (16.1–20.6%) is much higher than that of other PUFAs. The new FAs 23:5(n-6), 23:4(n-9), 24:4(n-10), and 24:5(n-7) have been found in the agglutinated foraminifera Crithionina sp., with their concentrations reaching 1.4%, 0.5%, 0.1%, and 1.6%, respectively. Lipids of the calcareous foraminifera Pyrgo sp. contained new 23:4(n-7), 24:4(n-8), 24:5(n-9), 24:6(n-6), and 26:5(n-3) PUFAs at concentrations of 0.4%, 0.4%, 1.7%, 0.9%, and 0.9%, respectively. The possible pathways of biosynthesis of these rare and new FAs in foraminifera are proposed. These PUFAs are not found in the bottom sediments inhabited by these foraminifera, but have been detected in lipids of various abyssal deposit-feeding invertebrates (echiurans, irregular echinoids and sea stars). The presence of new FAs, previously known only from foraminifera, in such benthic animals is a valuable supplement to the study of trophic relationships of these animals.