Irregular Echinoids Research Articles

OVULASTER PROTODECIMAE, N. SP. (ECHINOIDEA, SPATANGOIDA) AND ASSOCIATED EPIFAUNA (CIRRIPEDIA, VERRUCIDAE) FROM THE DANIAN OF NORTHEASTERN ITALY

A new species of irregular echinoid, Ovulaster protodecimae, is described from the Danian Scaglia Rossa Formation outcropping in the Venetian Prealps (Southern Alps, northeastern Italy). The new species, belonging to the order Spatangoida, is very distinctive because of its inflated, almost triangular test, the high-positioned periproct and the plate arrangement on the oral face. This is the first report of the genus Ovulaster in the Danian of Italy and the first description of an echinoid from the Early Palaeocene of Italy. One test has an epifauna of the sessile verrucid barnacle Verruca sp. cf. V. prisca Bosquet, 1854, attached on all except the oral surface.

New biostratigraphic data for the Chikkim Formation (Cretaceous, Tethyan Himalaya, India)

The Chikkim Formation as exposed in the Tethyan Himalaya (India) has been studied at its type locality, using planktonic foraminifera for a detailed biostratigraphic elaboration. Divided into two members, the Lower and Upper Chikkim members, this formation ranges in age from Albian to early Maastrichtian(?), and reaches a maximum thickness of 150 m. Examination of thin sections has yielded 34 species of foraminifera in five genus-level assemblages. The Lower Chikkim Member is about 55 m thick; its basal portion is of Albian age based on the presence of Biticinella breggiensis and Planomalina buxtorfi. At 26 m above the base, Whiteinella archaeocretacaea documents OAE 2 (Oceanic Anoxic Event 2), and thus the Cenomanian/Turonian boundary in this section. The carbonate sequence is capped by a Santonian-age hardground with iron oxide crusts and bioturbation. Macrofossils, including belemnites (at the base) and irregular echinoids (upper part), are present. The basal carbonaceous marls of the Upper Chikkim Member yield both large (benthic) rotaliid as well as planktonic foraminifera ( Globotruncanita elevata, Gl. stuartiformis, Gl. stuarti, Gansserina gansseri and others), indicating a Campanian age. The co-occurrence of Gl. elevata and G. gansseri in a single thin section results either from condensation or reworking in the basal part of the Upper Chikkim Member. Late Cretaceous index foraminifera such as Gl. elevata document deposition within the Tethyan Realm. The original thickness of the Upper Chikkim Member is uncertain, but would have been around 100 m; the unit appears markedly reduced through weathering at a height of about 5000 m above sea level. Equivalent sediments are exposed in the Zanskar area to the northwest, and in Nepal and Tibet. Cretaceous Oceanic Red Beds (CORBs) are probably missing due to the proximality of these pelagic settings.

An outstanding fauna of marsupiate echinoids in the Pliocene of Vendée (western France)

Abstract New investigations in the Pliocene deposits of Challans (Vendée) have allowed to collect more than 3000 marsupiate echinoids, remarkably preserved. So, apical systems, especially the marsupium of the breeding temnopleurids T. (V.) bigoti and C. bardini, have been described and figured for the first time with complete specimens. Two new marsupiate species have been described: Arbacina hugueti nov. sp., third marsupiate species of the genus Arbacina to be known in the Neogene of western France after A. emmae NÉRAUDEAU, 2003 from the Messinian of Brittany and A. pareyni ROMAN, 1983 from the Pliocene of Normandy; Tremaster romani, new species and genus of temnopleurid, characterised by an uncommon supra-ambital tuberculation, with excressences of the test surrounding scrobiculated tubercles. A third new marsupiate echinoid, Coptechinus sp. A, has been found too, but it is very difficult to know if it is a new species or a new morphotype of C. bardini. Contrarily to previous interpretations, this study points out the high diversity of western European Neogene marsupiate echinoids, a diversity comparable to the one of Australian Neogene marsupiate echinoids. However, breeding species from Australia and western Europe are clearly different and similarities exist between these two marsupiate echinofaunas at the family level only. Indeed, both in Australia and western Europe, the breeding species of echinoids mainly belong to the temnopleurid family, with the austral genus Paradoxechinus, on the one side, the north European genera Temnotrema and Coptechinus, on the other side. Moreover, the arbaciids consist of three marsupiate species of the genus Arbacina in Europe when no breeding species of this family exist in Australia. On the contrary, several breeding irregular echinoids have been found in the Australian Tertiary deposits (Spatangoids and Clypeasteroids) when not any marsupiate irregular echinoid has been discovered at present in the western Europe Neogene deposits.

Simplified dynamic model for the motility of irregular echinoids

Inspired by the locomotion mechanism of sea urchins, we study the locomotion of an irregular echinoid by means of a simplified dynamical model. We prove that if two conjectures are assumed, the geometrical arrangement of the five ambulacral petals of irregular echinoids should form a eutactic star in order to optimize motility. We firstly propose an adequate "measure" of eutacticity that allows us to to verify the statistical tendency to such a property for a representative collection of fossil specimens. Next, regarding dynamics, the biological advantage of eutactic stars is addressed as a minimal path problem. Finally, we study the stability of some eutactic stars under small perturbations.

Reproductive biology and biochemical composition of the brooding echinoid Amphipneustes lorioli on the Antarctic continental shelf

The bathyal West Antarctic Peninsula (WAP) shelf experiences intense seasonal variability in primary production, with summer phytoplankton blooms yielding intense pulse of phytodetritus to shelf sediments. Echinoderms form a conspicuous proportion of the deposit-feeding megabenthos on the shelf and of these Amphipneustes lorioli was the most abundant irregular echinoid. To explore the reproductive response of A. lorioli to this seasonal production cycle, A. Lorioli was sampled at one location on the WAP shelf during four separate cruises between March 2000 and March 2001. Reproductive patterns were determined by histological analyses of gonad tissue, and elemental (CHN) analyses were used to estimate the nutritional and energetic status of the body tissues. Histological analysis of the brooding echinoid A. lorioli suggested a quasi-continuous gametogenic pattern in both the ovaries and the testes. Biochemical analysis of the gonads and the gut tissues were consistent with a continuous gametogenic cycle, showing no significant changes in the biochemical composition of the tissues among seasons. Size-frequency distributions of the embryo and juvenile echinoids within the adults’ brood pouches revealed a synchronous recruitment of embryos and juveniles in specific cohorts between different adult specimens. Whilst this occurrence of different cohorts of the developing brood may be an adaptation to limited brood space, there may also be an external factor influencing the synchrony between adult individuals. Nonetheless, a continuous gametogenic cycle and the lack of seasonal variation in the biochemical composition of gonad and gut tissues suggest that this deposit-feeding irregular urchin is exploiting a persistent sediment food bank in WAP shelf sediments throughout much of the year.

Fasciole pathways in spatangoid echinoids: a new source of phylogenetically informative characters

Fascioles are important early-forming structures that play a key role in allowing irregular echinoids to burrow. They have traditionally been grouped into a small number of types according to their general position on the test, but this masks some significant differences that exist. The precise course that fasciole bands follow over the test plating has been mapped in detail for 89 species of spatangoid echinoids, representing the great majority of fasciole-bearing genera both living and fossil. Within each fasciole type, discrete and conserved patterns can be distinguished, differing both in which plates they are initiated on, and on whether they cross plate growth centres or are late-stage bands positioned towards the edge of the plate. Fasciole position is most highly conserved in the anterior and lateral interambulacral plates and on the earliest forming bands. The existence of different subanal fasciole patterns in the Micrasteridae and Brissidae suggests that these may have evolved independently. Schizasterid and hemiasterine spatangoids can each be subdivided into two major clades, and brissid spatangoids into three clades based on detailed patterns of their fascioles. Plotting fasciole pathways over test architecture provides a rich new source of phylogenetically informative characters. © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society, 2005, 144, 15−35.

Behavior of Pigment Cells Closely Correlates the Manner of Gastrulation in Sea Urchin Embryos

To know whether behavior of pigment cells correlates the process of gastrulation or not, gastrulating embryos of several species of regular echinoids (Anthocidaris crassispina, Mespilia globulus and Toxopneustes pileolus) and irregular echinoids (Clypeaster japonicus and Astriclypeus manni) were examined. In M. globulus and A. crassispina, the archenteron elongated stepwise like in well-known sea urchins. In the embryos of both species, fluorescent pigment cells left the archenteron tip and migrated into the blastocoel during gastrulation. In T. pileolus, C. japonicus and A. manni, on the other hand, the archenteron elongated at a constant rate throughout gastrulation. In these species, no pigment cell was observed at the archenteron tip during invagination processes; pigment cells began to migrate in the ectoderm from the vegetal pole side toward the apical plate without entering the blastocoel. These results clearly indicate that the behavior of pigment cells closely correlated the manner of gastrulation. Further, it was examined whether the archenteron cells are rearranged during invagination, by comparing the number of cells observed on cross sections of the archenteron at the early and late gastrula stages. The rearrangement was not conspicuous in A. crassispina and M. globulus, in which archenteron elongated stepwise. In contrast, the archenteron cells were remarkably rearranged in C. japonicus, alothough the archenteron elongated continuously. Thus, neither the behavior of pigment cells nor the manner of gastrulation matches the current taxonomic classification of echinoids.

Phylogeny and Systematics of Holasteroid Echinoids and Their Migration Into the Deep‐sea

Holasteroids are a major clade of irregular echinoids that today is confined to the deep‐sea, but which has a rich fossil record extending back to the start of the Cretaceous Period. A cladistic analysis of this clade, encompassing the great majority of living and fossil genera, is undertaken based on new data on test architecture. The classification of the group is reviewed and a new hierarchical scheme is proposed. The highly atypical apical disc structure of pourtalesiid holasteroids is discussed and critical data for understanding its plate homologies are provided by the most primitive pourtalesiid, the Late Cretaceous Galeaster. This supports the idea that plates previously identified as posterior genital plates in pourtalesiids are in fact ocular plates II and IV. An evolutionary tree for holasteroids is constructed by calibrating the cladogram against the stratigraphic record. This is then used to examine how holasteroid diversity and ecology have changed through time. Holasteroids have migrated into the deep‐sea at least four times independently. Three of these lineages can be traced back to sister taxa living in deep‐water continental shelf environments in the Late Cretaceous–early Tertiary, while a fourth represents a very much younger migration event, possibly Late Miocene in age.

A Late Jurassic Carbonate Ramp Colonized by Sponges and Benthic Microbial Communities (External Prebetic, Southern Spain)

Abstract During the Middle to Late Oxfordian (locally ranging into the earliest Kimmeridgian), the epicontinental shelf that persisted in the southeastern paleomargin of Iberia (Prebetic Zone) was largely colonized by siliceous sponges (Dictyida, Lychniskida, and Lithistida, in descending order of abundance). Spongiolithic lithofacies (sponge-rich deposits in which buildups are rare and small) represent a marine environment extensively colonized by sponges in the form of large sponge meadows showing associated epibenthic organisms (brachiopods, bivalves, and echinoderms). Marl-limestone rhythmites represent muddy bottoms colonized by scarce endobenthos (bivalves and irregular echinoids). However, the occurrence of patchy sponge bioherms provided a favorable substrate for epibionts and microbial lithoherms (microbialites). The record of meter-scale buildups showing sponge bioherm-microbial lithoherm in marl-limestone rhythmites resulted from the preferred colonization of sponge patches by benthic microbial...

Echinoid assemblages as a tool for palaeoenvironmental reconstruction – an example from the Early Miocene of Egypt

A rich Lower Miocene echinoid fauna has been investigated from Gebel Gharra, NW of Suez, Egypt. The ca 140 m long section consists of a siliciclastic lower part and a carbonate-dominated upper part. This corresponds to a general transgression/regression cycle. In all, 27 different echinoid taxa were recognised. The level of taxonomic identification varies depending on test completeness and preservation of specific morphological characters. The palaeoecology of the echinoids was inferred using a functional morphological approach and actualistic comparisons. A wide variety of ecological habitats are represented with the presence of regular as well as irregular sea urchins; epibenthic as well as endobenthic forms, as well as a wide range of interpreted burrowing depths for different irregular echinoids. Seven different echinoid assemblages were distinguished, which differ with respect to the species diversity, skeletal taphonomy and sedimentary environment: (1) the Parascutella Assemblage displays spectacular mass accumulations of sand dollars accumulated by proximal storm deposits and winnowing; (2) the Cidaroid–Echinacea Assemblage represents a slightly deeper, moderate-energy environment with a highly structured habitat and corresponding variety of regular and irregular sea urchins; (3) a Spatangoid Assemblage with a diverse fauna of burrowing echinoids; (4) the Transported Assemblage represents an allochthonous collection of echinoids from shallow-water, coarse sandy substrates; (5) the Mixed Assemblage representing a slightly shallower, low- to moderate-energy environment with reduced sedimentation rates; (6) a Clypeaster martini Assemblage characterising a shallow, higher-energy environment; (7) finally, the poorly diverse Phyllacanthus Assemblage from shallow-water carbonates. Diversity variations within the assemblages are correlated primarily to substrate variation, burrowing depths as well as taphonomic factors. The transgression/regression cycle is well reflected by the echinoid assemblages, which show a general deepening of depositional environment followed by shallowing upward tendencies.

Combining embryology and paleontology: origins of the anterior-posterior axis in echinoids

The tendency of the periproct to move outside the apical system occurred in eight independent sea urchins lineages, but only one succeeded. The origin of the anterior-posterior axis in irregular echinoids results from that successful attempt, and is primarily achieved by eccentricity of the periproct. The mechanism by which this occurs is best understood through synthesis of data from embryology, paleontology, and phylogenetics. In irregular echinoids, the complete escape of the periproct from the apical system (exocyclism) is a consequence of changes in the embryological sequence that governs periproctal eccentricity. The adaptative significance of this change is discussed. To cite this article: T. Saucède et al., C. R. Palevol 2 (2003).

Completeness of a fossil record: the Pleistocene echinoids of the Antilles

Diversity of Pleistocene marine invertebrates with single component, robust, easily identifiable skeletons shows a good correspondence to that of the Recent when compared between similar environments in the same region. Such comparisons are less easily made for multi-element skeletons. In the Antilles there are 24 extant species of echinoids in 0–30 m water depth. Considering all available fossils - complete tests, disarticulated spines, and test fragments and ossicles - the Pleistocene echinoids of the Antillean region have a high similarity with the extant shallow water fauna (c. 63% specific and 72% generic similarity). Many of the extant, shallow water, regular echinoid taxa are known from the Pleistocene, although irregular echinoids are less well represented. These results are comparable with those determined for coeval benthic invertebrates from this and other geographic regions, and indicate a high degree of similarity from a survey which is so far limited to only a few of the islands. Not all Pleistocene units considered herein were deposited in shallow water, but they include autochthonous specimens of taxa whose depth range extends beyond shallow water at the present day or presumed allochthonous specimens derived by downslope transport from shallower water, or both.

Oichnus Bromley Borings in the Irregular Echinoid Hemipneustes Agassiz from the Type Maastrichtian (Upper Cretaceous, The Netherlands and Belgium)

Three ichnospecies of Oichnus Bromley occur in tests of the large holasteroid echinoid Hemipneustes striatoradiatus (Leske) in the type area of the Maastrichtian (Upper Cretaceous) in The Netherlands and Belgium; Oichnus simplex Bromley (penetrative), Oichnus paraboloides Bromley (nonpenetrative and showing two distinct morphologies), and Oichnus excavatus isp. nov. (nonpenetrative). The two distinct morphologies of O. paraboloides (both shallow, one with a central boss) are gregarious, but do not occur together on the same specimens, suggesting they were generated by different taxa. Oichnus paraboloides with a central boss occurs on H. striatoradiatus from the upper Nekum Member, Maastricht Formation (Maastrichtian, Upper Cretaceous). Tests of the host echinoid are smaller in the overlying Meerssen Member, Maastricht Formation, where they are infested by O. excavatus, the largest borings considered herein, which have concave walls and a large central boss. Blisters inside tests from the Meerssen Member show that this infestation occurred when the echinoid was alive. It is postulated that producers of these borings in H. striatoradiatus may have been genetically related and increased in size during the Maastrichtian even as the host echinoids showed a size decrease. This size increase in H. striatoradiatus was genetic and cannot be related to increase in size of borings.

Regularity in irregular echinoids.

Using the mathematical concept of eutactic star, we prove that it is possible to define a morphospace for irregular echinoids by using a single parameter. In particular, we have found an extraordinary geometric property in the flower-like patterns of the five ambulacral petals of these animals. This property is fulfilled with great accuracy for a large collection of fossil specimens and provides new insights in the study of the viable skeletal designs of extinct and/or living organisms.

Oichnus Bromley Borings in the Irregular Echinoid Hemipneustes Agassiz from the Type Maastrichtian (Upper Cretaceous, The Netherlands and Belgium)

Oichnus Bromley Borings in the Irregular Echinoid Hemipneustes Agassiz from the Type Maastrichtian (Upper Cretaceous, The Netherlands and Belgium)

Changing biodiversity of Mediterranean irregular echinoids from the Messinian to the Present-Day

Morphological and palaeoecological changes in irregular echinoid diversity during the Late Miocene Messinian stage have been analysed at the scale of the Sorbas Basin of southeast Spain. Biometrical and statistical analyses established the validity of species differentiation. An example is given for Messinian, Pliocene and Recent Schizaster species: S. saheliensis and S. canaliferus. Palaeoecological analyses show that irregular echinoid faunas record environmental changes, especially sea-level variations, with contrasting ecomorphological gradients for deepening and shallowing trends. Deepening is indicated by the stratigraphic succession of Clypeaster altus, associated Clypeaster marginatus– Spatangus– Schizaster and then Brissopsis species whereas shallowing is indicated by the opposite succession. The survival of Brissopsis, typically a stenohaline and relatively deep marine organism, in the marls interbedded within the uppermost Messinian gypsum of the Sorbas Basin testifies to the existence of marine connexions between this basin and other Mediterranean marine areas during the end of the evaporitic episode. Tabulation of irregular echinoid species diversity at eight time intervals between the Tortonian/Messinian boundary and the present-day (inclusive) for the Mediterranean Basin as a whole indicates a progressive increase in diversity from the latest Tortonian to the upper part of the pre-evaporitic Messinian before a fall in diversity during the salinity crisis. However, survivals after the crisis are very numerous, representing 78% of the maximum pre-evaporitic value.

The oldest deep-sea Ophiomorpha and Scolicia and associated trace fossils from the Upper Jurassic–Lower Cretaceous deep-water turbidite deposits of SW Bulgaria

Deep-sea trace fossils of the Nereites ichnofacies occur in the uppermost Kimmeridgian–Berriasian deep-water turbidite deposits of the Kostel Formation in SW Bulgaria. The trace fossil assemblage contains Tithonian Ophiomorpha isp. and Ophiomorpha annulata, which are the oldest deep-sea representatives of this ichnogenus. They indicate much older invasion of Ophiomorpha into deep-sea, which was hitherto dated as to mid-Cretaceous. It is not clear whether the invasion failed or Ophiomorpha survived in deep-sea refuge and became widespread after improving oxygenation of the deep seas after the Cenomanian/Turonian anoxic event. Tithonian Scolicia, produced by irregular echinoids, exhibits a similar distribution pattern.

Evolution of Caribbean echinoderms during the Cenozoic: moving towards a complete picture using all of the fossils

In the Antillean region, collecting bias towards complete tests has engendered a lop-sided view of the diversity of the echinoderms through time. Crinoids, asteroids and ophiuroids, as well as certain echinoid groups, are widespread as fossils, but are only preserved as disarticulated or broken fragments that have commonly been ignored in studies of faunal diversity. Utilization of these disarticulated remains and collection of specimens from units that have hitherto been considered to lack common fossil echinoderms (such as the Plio-Pleistocene of many islands) is resulting in a more consistent synthesis of their regional diversity during the Cenozoic. Both echinoids and stalked crinoids show distinctive faunal changes following the Eocene–Oligocene extinction events, with the roots of their modern components appearing in the region at that time, at least at the generic level. In contrast, distinctive asteroid species that are recognised from the Oligocene do not appear to have persisted into the later Cenozoic of the region. Incorporation of data from disarticulated elements commonly indicates that regular echinoids were at least as diverse as irregular echinoids. Some taxa that are common in the Caribbean at the present day, such as diadematoids, that apparently lacked a recognisable fossil record due to taphonomic factors, are recognised from throughout the Cenozoic on the basis of distinctive disarticulated ossicles.

British Cretaceous Echinoids

Part 6 continues the description of the irregular echinoids from the British Cretaceous, dealing exclusively with the cassiduloid genera. Cassiduloids are restricted to the more inshore, sandy facies in the British Cretaceous and are thus absent above the Cenomanian when chalk facies predominate. Sixteen species, belonging to eleven genera are described. One new species, Ochetus pauli, is described, and the new subfamily Stigmatopyginae is proposed. Three genera, Clypeopygus, Pygopistes and Penesticta, represent new records for the British Cretaceous.

Echinoids from the Cretaceous/Tertiary boundary sequence at Byala, Varna Area, Bulgaria

The study is based оn fossil material from four K/T bоundаrу sесtiоns nеаr the tоwn of Byala, Vаrnа District. The есhinоids form аn еssеntiаl part of the fossil mасrоfаunа at these outcrops. The рrеsеnсе of аmmоnitеs, inосеrаmids and nannoplankton is а good basis for precising of their stratigraphical range. The collection consists of 305 specimens, rерresentatives of 23 species from 5 families. The composition and distribution of the irregular echinoids from uninterrupted кrr sections show а gradual decrease in species variety at the end of the Late Maastrichtian. We should note the extinction of the genera Stegaster, Sеиnаstеr, Lampadaster and Cardiaster. А complete change of the echinoid species is observed at the boundary without evidence of mass mortality. The surviving genеrа аrе Coraster, Echinocorys and Galeaster. The new elements in post-maastrichtian fauna in these sections аrе representatives of the genera Ornithaster, Homoeaster, Cyclaster. There is а blооm in development of these Paleocene species, but all of them have ancestors in Maastrichtian. The K/T boundary is distinct only оn species and generic level. The echinoid communities from Byala аrе typical for the Thetyan basin.