Urchins in the Meadow: Paleobiological and Evolutionary Implications of Cidaroid Predation on Crinoids

Deep-sea submersible observations made in the Bahamas revealed interactions between the stalked crinoid Endoxocrinus parrae and the cidaroid sea urchin Calocidaris micans. The in situ observations include occurrence of cidaroids within “meadows” of sea lilies, close proximity of cidaroids to several upended isocrinids, a cidaroid perched over the distal end of the stalk of an upended isocrinid, and disarticulated crinoid cirri and columnals directly underneath a specimen of C. micans. Guts of two C. micans collected from the crinoid meadow contain up to 70% crinoid material. Two of three large museum specimens of another cidaroid species, Histocidaris nuttingi, contain 14–99% crinoid material. A comparison of cidaroid gut contents with local sediment revealed significant differences: sediment-derived material consists of single crinoid ossicles often abraded and lacking soft tissue, whereas crinoid columnals, cirrals, brachials, and pinnulars found in the cidaroids are often articulated, linked by soft tissue, and unabraded. Furthermore, articulated, multi-element fragments often show a mode of fracture characteristic of fresh crinoid material. Taken together, these data suggest that cidaroids prey on live isocrinids. We argue that isocrinid stalk-shedding, whose purpose has remained a puzzle, and the recently documented rapid crawling of isocrinids are used in escaping benthic predators: isocrinids sacrifice and shed the distal stalk portion when attacked by cidaroids and crawl away, reducing the chance of a subsequent encounter. If such predation occurred throughout the Mesozoic and Cenozoic (possibly since the mid-Paleozoic), several evolutionary trends among crinoids might represent strategies to escape predation by slow-moving benthic predators

Origin and evolutionary plasticity of the gastric caecum in sea urchins (Echinodermata: Echinoidea)

Background: The digestive tract of many metazoan invertebrates is characterized by the presence of caeca or diverticula that serve secretory and/or absorptive functions. With the development of various feeding habits, distinctive digestive organs may be present in certain taxa. This also holds true for sea urchins (Echinodermata: Echinoidea), in which a highly specialized gastric caecum can be found in members of a derived subgroup, the Irregularia (cake urchins, sea biscuits, sand dollars, heart urchins, and related forms). As such a specialized caecum has not been reported from "regular" sea urchin taxa, the aim of this study was to elucidate its evolutionary origin. Results: Using morphological data derived from dissection, magnetic resonance imaging, and extensive literature studies, we compare the digestive tract of 168 echinoid species belonging to 51 extant families. Based on a number of characters such as topography, general morphology, mesenterial suspension, and integration into the haemal system, we homologize the gastric caecum with the more or less pronounced dilation of the anterior stomach that is observed in most "regular" sea urchin taxa. In the Irregularia, a gastric caecum can be found in all taxa except in the Laganina and Scutellina. It is also undeveloped in certain spatangoid species. Conclusions: According to our findings, the sea urchin gastric caecum most likely constitutes a synapomorphy of the Euechinoidea. Its occurrence in "regular" euechinoids is linked to the presence of an additional festoon of the anterior stomach in ambulacrum III. Both structures, the additional festoon and the gastric caecum, are absent in the sister taxon to the Euechinoidea, the Cidaroida. Since the degree of specialization of the gastric caecum is most pronounced in the predominantly sediment-burrowing irregular taxa, we hypothesize that its evolution is closely linked to the development of more elaborate infaunal lifestyles. We provide a comprehensive study of the origin and evolutionary plasticity of a conspicuous digestive tract structure, the gastric caecum, in a major taxon of the extant invertebrate macrozoobenthos. © 2010 Ziegler et al; licensee BioMed Central Ltd.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

A new late Cenozoic species of Abertella (Echinoidea: Clypeasteroida) from Patagonia

A new species of abertellid sand dollar, Abertella miskellyi n. sp., is described from the Miocene Camarones Formation of Patagonia, southern Argentina. The new taxon corroborates the existence of the genus in South America, given that Abertella is most common in the southeastern USA and the eastern coast of Central America. It is characterized by a unique basicoronal circle, in which the interambulacral basicoronal plates are very heterogeneous in size (small in interambulacrum 5, largest in interambulacra 2 and 3). Additionally, it features disjunct oral interambulacra involving two ambulacral plates in some of the interambulacra rather than one, thus being the most disjunct of all known species of Abertella. A key to the species of the genus is provided.Fil: Kroh, Andreas. Naturhistorisches Museum Wien; AustriaFil: Mooi, Rich. California Academy of Sciences. Department of Invertebrate Zoology and Geology; Estados UnidosFil: del Rio, Claudia Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; ArgentinaFil: Neumann, Christian. Museum für Naturkunde. Leibniz Institute for Research on Evolution and Biodiversity; Alemani

The Magnitude of Global Marine Species Diversity

Background: The question of how many marine species exist is important because it provides a metric for how much we do and do not know about life in the oceans. We have compiled the first register of the marine species of the world and used this baseline to estimate how many more species, partitioned among all major eukaryotic groups, may be discovered. Results: There are ∼226,000 eukaryotic marine species described. More species were described in the past decade (∼20,000) than in any previous one. The number of authors describing new species has been increasing at a faster rate than the number of new species described in the past six decades. We report that there are ∼170,000 synonyms, that 58,000–72,000 species are collected but not yet described, and that 482,000–741,000 more species have yet to be sampled. Molecular methods may add tens of thousands of cryptic species. Thus, there may be 0.7–1.0 million marine species. Past rates of description of new species indicate there may be 0.5 ± 0.2 million marine species. On average 37% (median 31%) of species in over 100 recent field studies around the world might be new to science. Conclusions: Currently, between one-third and two-thirds of marine species may be undescribed, and previous estimates of there being well over one million marine species appear highly unlikely. More species than ever before are being described annually by an increasing number of authors. If the current trend continues, most species will be discovered this century

Living Cassiduloids (Echinodermata, Echinoidea) - A Key And Annotated List

Volume: 103Start Page: 63End Page: 8

Podial Particle Picking in Cassidulus caribaearum (Echinodermata: Echinoidea) and the Phylogeny of Sea Urchin Feeding Mechanisms

Volume: 191Start Page: 209End Page: 22

RESOURCE PARTITIONING BY SAND DOLLARS IN CARBONATE AND SILICEOUS SEDIMENTS: EVIDENCE FROM PODIAL AND PARTICLE DIMENSIONS

Volume: 171Start Page: 197End Page: 20

Radial symmetry, the anterior/posterior axis, and echinoderm Hox genes.

20 pagesInternational audienceThe strangeness of echinoderm pentaradiality results from superposition of radial symmetry onto ancestral deuterostome bilaterality. The Extraxial- Axial Theory shows that echinoderms also have an anterior/posterior (A/P) axis developed independently and ontogenetically before radiality. The A/P axis is first established via coelomic stacking in the extraxial region, with ensuing development of the pentamerous hydrocoel in the axial region. This is strongly correlated with a variety of gene expression patterns. The echinoid Hox cluster is disordered into two different sets of genes. During embryogenesis, members of the posterior class demonstrate temporal, spatial, and genetic colinearity within the extraxial region.We suggest that displacement of genes from the more anterior Hox classes toward the 5' end of the chromosome leads to control of the later-developing, radially symmetric axial region. Genetic disorder is therefore another way of using colinearity to build the unique echinoderm symmetry

How Hox genes can shed light on the place of echinoderms among the deuterostomes.

19 pagesInternational audienceBACKGROUND: The Hox gene cluster ranks among the greatest of biological discoveries of the past 30 years. Morphogenetic patterning genes are remarkable for the systems they regulate during major ontogenetic events, and for their expressions of molecular, temporal, and spatial colinearity. Recent descriptions of exceptions to these colinearities are suggesting deep phylogenetic signal that can be used to explore origins of entire deuterostome phyla. Among the most enigmatic of these deuterostomes in terms of unique body patterning are the echinoderms. However, there remains no overall synthesis of the correlation between this signal and the variations observable in the presence/absence and expression patterns of Hox genes. RESULTS: Recent data from Hox cluster analyses shed light on how the bizarre shift from bilateral larvae to radial adults during echinoderm ontogeny can be accomplished by equally radical modifications within the Hox cluster. In order to explore this more fully, a compilation of observations on the genetic patterns among deuterostomes is integrated with the body patterning trajectories seen across the deuterostome clade. CONCLUSIONS: Synthesis of available data helps to explain morphogenesis along the anterior/posterior axis of echinoderms, delineating the origins and fate of that axis during ontogeny. From this, it is easy to distinguish between 'seriality' along echinoderm rays and true A/P axis phenomena such as colinearity within the somatocoels, and the ontogenetic outcomes of the unique translocation and inversion of the anterior Hox class found within the Echinodermata. An up-to-date summary and integration of the disparate lines of research so far produced on the relationship between Hox genes and pattern formation for all deuterostomes allows for development of a phylogeny and scenario for the evolution of deuterostomes in general, and the Echinodermata in particular