Echinoid Species Research Articles

Urchins on the edge: an echinoid fauna with a mixed environmental signal from the Eocene of Jamaica

An echinoid fauna from the Early–Middle Eocene of Jamaica has yielded six species of echinoid: the phymosomatoid Acanthechinus peloria (Arnold and Clark); the oligopygoid Oligopygus sp.; the clypeasteroids Fibularia jacksoni Hawkins and Neolaganum sp.; and the spatangoids Eupatagus alatus Arnold and Clark and Eupatagus sp. cf. E. clevei (Cotteau). Eupatagus alatus has a relatively low test, is broadest posterior of centre, and lacks an anterior sulcus; Eupatagus sp. cf. clevei is relatively higher and more inflated, more parallel-sided, and blunter anteriorly with an anterior sulcus. The discovery of F. jacksoni and Neolaganum sp. together with Oligopygus sp. is unexpected, as these species commonly have different ecological niches in the Eocene of Jamaica. In previous examples described from the Eocene succession of the island, oligopygoids favoured high-energy shelf edge settings, whereas Fibularia and neolaganids prefered low-energy lagoonal settings. The assemblage as a whole likely represents an Early–Mid Eocene echinoid fauna inhabiting a shallow island shelf sea, in a transition between shelf edge and lagoonal setting.

Deep-sea echinoids and holothurians (Echinodermata) near cold seeps and coral communities in the northern Gulf of Mexico

Seven National Oceanic and Atmospheric Administration and United States Geological Survey expeditions employed manned submersibles or remotely operated vehicles to explore deep-sea coral and cold seep habitats in the northern central Gulf of Mexico continental slope, off Mississippi and Louisiana. Ten species of echinoids and 21 species of holothurians were collected and/or documented by still photography or videography in a relatively small area, in depths of 309-2549 m. New information on ecology, behavior, and distribution of echinoids and holothurians is provided. A new genus name is proposed to replace Meseres Ludwig, 1893, which is preoccupied. Myriotrochus ahearnae, a new species of apodous myriotrochid holothurian, is described.

Turonian-Santonian echinoids from Wadi Qena, Eastern Desert, Egypt; a new arrangement of apical disc plating in spatangoids

Eighteen echinoid species (seven regular and eleven irregular) belonging to twelve genera have been described from the Turonian-Santonian succession of two sections located in the northern part of Wadi Qena, Eastern Desert. The diversity of the recorded species is low in the Turonian (six species), but comparatively high in the Coniacian-Santonian (twelve species). Of the recorded species, Most of these species (72%) are recorded for the first time from Wadi Qena area, one left in open nomenclature, Mecaster sp., represents a new species, and two, Phymosoma microtuberculatum and Thylechinus (T.) said, represent new records for Egypt. The taxonomic rank of Parapygus sudrensis has been changed. Phymosoma microtuberculatum which is known from the ‘Senonian’ of southwest Europe is recorded herein in the lower Turonian. Two echinoid assemblage zones are recognizable in each of the studied two sections. They are correlated with other fossil assemblage zones in Egypt. Faunal affinity and paleobiogeography of the species are discussed. A new arrangement of apical disc plating in spatangoids is described and discussed.

Notatudiadema and Aegyptiaris: Two new regular echinoids genera with two new species from the Cenomanian of north Sinai, Egypt

Revision of the Cenomanian echinoids deposited in the Cairo Geological Museum resulted in the erection of two new genera with two new species of regular echinoids. The first, Notatudiadema rekeibensis gen. and sp. nov. is established for specimens from the Cenomanian of Gabal El-Rekeib, southeast the Maghara massif, north Sinai to accommodate diadematoid echinoids having hemi-crenulate ambital and sub-ambital interambulacral tubercles with the adapical part of platform non-crenulate and the adoral one of same tubercle coarsely crenulate. The second is Aegyptiaris halalensis gen. and sp. nov., erected for material from the lower Cenomanian of Gabal El-Halal, northeast Sinai as an emiratiid echinoid with throughout polyporus ambulacra and extremely reduced adapical ambulacral tubercles. The functional morphology and paleobiology of these taxa are also discussed. A new family is established: family Monodiadematidae fam. nov.

Primeros registros de equinodermos (Echinodermata) en aguas someras de Corn Island, Caribe, Nicaragua

There are few works on ecology and diversity of echinoderms in Nicaragua. Studies of many faunal groups of marine invertebrates, in particular which should focus on the fauna of tropical areas, have been scarce or have received only limited attention from the scientific community and government authorities of the South Atlantic Autonomous Region (RAAS) of Nicaragua. Scientific research on these groups has targeted mainly resources of commercial importance (e.g. spiny lobster, Panulirus argus). There is lack of information regarding the faunal biodiversity of Corn Island in general. The echinoderm fauna studied in this work comes from a wide variety of environments, from the rocky coastal area, sandy beaches, sea grass to areas of coral reef. Echinoderms were collected, from 14 points in a variety of marine substrates, aided by SCUBA diving equipment during the period from August 2012 to March 2013. There was a total of 41 species corresponding to four classes: three species of Asteroids, 16 species of ophiuroids, 11 species of Echinoids and 11 species of holoturoids. The most common species was Ophiolepis impressa present in ten of the 14 localities, followed of Diadema antillarum, Eucidaris tribuloides and Ophioderma cinerea who were present at seven locations each, respectively. The less common species were Clypeaster rosaceus, Leodia sexiesperforata, Meoma ventricosa and Ophioderma guttata. The study of echinoderms in diverse marine habitats facilitates the comparison of the state of fluctuation of those communities along time. Whether they were natural or caused by human activities. Therefore, the present study expands knowledge about the species of echinoderms that live in shallow areas of Corn Island (between 0-10 m depth), so able to establish measures for the conservation of these species.

Brachiopods and echinoids from the lower Cenomanian of Koraćica (Kosmaj Mountain, central Serbia)

Two brachiopod species belonging to two genera, two families, and one order and nine echinoid taxa (five regular and four irregular) belonging to eight genera, seven families, and seven orders are revised and systematically described from reddish coarse-grained bioclastic packstones to rudstones of the Grab spring section (Kosmaj Mountain) of the Vardar Zone of central Serbia. The stratigraphic range and the palaeobiogeographic distribution are given for each species. Five echinoid species, “Cidaris” strombecki (Desor, 1858), Leptosalenia cf. prestensis (Desor, 1856), Tetragramma variolare subnudum (Agassiz, 1846), Conulus (Conulopyrina) vionneti (Desor, 1857), and C. (Conulus) castanea (Brongniart, 1822) are recorded from the lower Cenomanian of Serbia for the first time. Earlier on, the benthic macrofauna of the section has been assigned an Albian–Cenomanian age. Although the upper Albian–lower Cenomanian boundary is covered by debris, the presence of the lower Cenomanian larger foraminiferal zone [Orbitolina (Conicorbitolina) conica] allows to assign the lower part of the Cenomanian succession certainly to the lower Cenomanian. The O. (C.) conica Zone overlies the uppermost Albian planktonic foraminiferal Thalmanninella appenninica and the ammonite Puzosia planulata zones. Most of the brachiopods and echinoids are predominantly confined to the northern margin of the Tethyan realm and some species are also known from the southern margin of the Tethys and from north-eastern Brazil. The distribution patterns of the taxa were probably influenced by east-west directed currents during the early Cenomanian time. The identified taxa are associated with other macrofaunal elements such as ammonites, bivalves, gastropods, and corals. The presence of stenohaline groups document euhaline conditions. The high degree of fragmentation, disarticulated bivalves, and the upward oriented of the adoral surfaces of most echinoids suggest that the organisms lived in moderately agitated subtidal environments and suffered post-mortem transport.

Badenian (Middle Miocene) echinoids and starfish from western Ukraine, and their biogeographic and stratigraphic significance

Abstract Echinoderms from the Badenian (Middle Miocene) of the Fore-Carpathian Basin of western Ukraine are facies restricted. The Mykolaiv Beds, stratigraphically older, yielded the starfish Astropecten forbesi (complete skeletons), two genera of sand dollars (Parascutella, Parmulechinus), and numerous other echinoids of the genera Psammechinus , Echinocyamus, Spatangus, Hemipatagus, Echinocardium, Clypeaster, Echinolampas, and Conolampas. The stratigraphically younger, calcareous Ternopil Beds yielded Eucidaris (complete coronae, isolated spines), Arbacina , Brissus, and Rhabdobrissus. Sixteen species of echinoids are distinguished and/or commented. A new brissid, Rhabdobrissus tarnopolensis sp. nov., is established. A mass occurrence of some species (Psammechinus dubius and Hemipatagus ocellatus) contrasts with that of mass aggregations (sand dollars and Echinocardium leopolitanum) by dynamic events in selected layers of proximal tempestites. Of special note is the occurrence of very small specimens, interpreted as juveniles (‘babies’) having been swept out of their restricted biotopes (‘nurseries’). Some species hitherto regarded as of Early Miocene age, and the problem of their persistence beyond the Fore-Carpathian Basin and/or migration into that basin during the Middle Miocene transgression are discussed.

Middle–upper Cenomanian echinoids from north Wadi Qena, North Eastern Desert, Egypt

Two Upper Cretaceous (middle–upper Cenomanian) sections located at the northern part of Wadi Qena were measured and their echinoids were collected carefully bed by bed. This area is abnormally rich in echinoids where their diversity is high and also many species are abundant. Twenty-three echinoid species (10 regular and 13 irregular) referred to twelve genera have been identified and taxonomically described. Two new species are established: Pedinopsis hemisphaerica and Phymosoma elqotti. The taxonomic rank of two species is changed. Three species, which are described from the Cenomanian of Algeria and Tunisia, are new records from Egypt. Phymosoma major Coquand, which is common in the Turonian of North Africa and south Europe, is recorded here in the Late Cenomanian for the first time. The echinoid Anorthopygus Cotteau, 1859 and its species are revised. Three echinoid assemblage zones are delineated in each of the two studied sections. They are compared to other macro-faunal assemblage zones in the Cenomanian at different parts in Egypt. The palaeobiogeography of the echinoids in the present study is discussed.

Echinoid community structure and rates of herbivory and bioerosion on exposed and sheltered reefs

Echinoid–habitat relations are complex and bi-directional. Echinoid community structure is affected by the habitat structural and environmental conditions; while at the same time, echinoids may also act as ‘reef engineers’, able to alter marine environments on a wide geographic scale. In particular, echinoids play a major role in bioerosion and herbivory on coral reefs. Through feeding, echinoids reduce algal cover, enabling settlement and coral growth. However, at the same time, they also remove large parts of the reef hard substrata, gradually leading to reef degradation. Here, we compared coral and macroalgal abundance, echinoid community structure and species-specific rates of echinoid herbivory and bioerosion on reefs subjected to different intensities of oceanic exposure. Spatio-temporal variations in coral and macroalgal cover were monitored, and populations of the four most abundant echinoid species on the coral reefs of Zanzibar – Diadema setosum (Leske), Diadema savignyi (Michelin), Echinometra mathaei (de Blainville) and Echinothrix diadema (Linnaeus) – were compared between the Island's eastern exposed reefs and western sheltered ones. To account for the effect of management in the context of reef exposure, we included marine protected areas (MPAs) of both types of reef categories (i.e. sheltered and exposed) in our comparison. Coral and macroalgal cover presented a conspicuous contrasting pattern across exposed and sheltered sites. While coral dominance and lack of macroalgae were prominent on sheltered reefs, an opposite trend of low coral cover and moderate–high macroalgal cover were found on exposed reefs. Bioerosion was also significantly higher on exposed reefs than on sheltered ones (4.2–13 and 1.2–3.9kg CaCO3m−2year−1, respectively). The highest rates, recorded on Pongwe, with almost 7kg CaCO3m−2year−1, are among the highest echinoid bioerosion rates known to date. Management had a substantial effect on habitat and echinoid community structure, as coral cover was significantly higher, macroalgal cover lower, and echinoid densities generally reduced on MPAs regardless of exposure intensity. Our findings suggest that exposed reefs are susceptible to markedly higher degrees of echinoid bioerosion; however, adequate management measures can significantly reduce these rates, consequently altering the reef's trajectory for degradation.

Integrated biostratigraphy and stage boundaries of the Abderaz Formation, east of the Kopeh-Dagh sedimentary basin, NE Iran

The foraminiferal content of the well-known, foraminifera-rich Abderaz Formation of the Kopeh-Dagh basin in northeastern Iran was analyzed to determine biostratigraphy, age dating, chronostratigraphy and evolutionary trends. The Abderaz Formation was sampled at the following four sections: the Qarehso section, the Abderaz village section, the Muzduran section and the Shorab section. The Qarehso section is approximately 540 m thick and consists of 77 planktonic foraminifera species belonging to 18 genera in 5 biozones, 10 echinoid species belonging to 4 genera and 8 inoceramid species belonging to 5 genera. Based on this fossil content, the Qarehso section was dated to the lowermost Turonian to the upper Santonian. Based on the first occurrence datums of Cremnoceramus walterdorfensis walterdorfensis and Cremnoceramus deformis deformis and on the FODs of Micraster cortestudinarium and Dicarinella concavata, the Turonian–Conician boundary was detected in this section. In addition, based on the FODs of Echinocorys gr. scutata forma vulgaris, Echinocorys gr. scutata forma vulgaris-planodama and Di. Asymetrica, the base of the Santonian stage was also detected in the Qarehso section. The Abderaz village section is 556.5 m thick and contains 17 genera and 68 species of planktonic foraminifera that have been identified in 9 biozones and 7 genera and 15 species of invertebrates. The lowermost Turonian to the lowermost Campanian ages have been established in the Abderaz Formation. In the Abderaz village section, 3 boundaries were identified. Based on the FODs of Cremnoceramus walterdorfensis walterdorfensis, C. deformis deformis and C. crassus crassus and on the FODs of Contusotruncana fornicata and C. pateliformis, the base of the Coniacian stage was identified. Based on the FODs of Di. asymetrica and Macroglobigerinelloides alvarezi, the Coniacian–Santonian boundary was identified. Additionally, based on the extinction of the Marginotruncanid group and on the LOD of Pseudotextularia nuttalii, the base of the Campanian stage was identified. The Muzduran section of the Abderaz Formation is 400 m thick and contains 59 planktonic foraminifera species belonging to 19 genera, 10 inoceramid species belonging to 5 genera, 5 echinoid species belonging to 3 genera and 2 ammonite species belonging to 2 genera. Also based on this fossil content, the age of the formation is estimated to be the middle Turonian–early Campanian. In the Muzduran section, the base of the Coniacian stage was detected just below the first occurrence of C. deformis deformis, whereas the bases of the Santonian and Campanian stages were found at the first occurrence of Echinocorys ex gr. scutata and the LOD of the Marginotruncanids groups and of Ventilabrella austiniana, respectively. The Shorab section is 360 m thick. In this section, 51 planktonic foraminifera species belonging to 16 genera were identified, and 5 biozones were differentiated. In addition, 1 ammonite species and 8 inoceramid species belonging to 4 genera were found in this section. Based on this fossil assemblage, the age of the Shorab section dates to the lowermost Turonian–early Campanian. In this section, the study of macro- and microfauna shows three boundaries: the Turonian–Coniacian, Coniacian–Santonian and Santonian–Campanian boundaries. The base of the Coniacian stage was identified based on the FODs of the planktonic foraminifera Archaeoglobigerina cretacea and Dicarinella concavata, along with the FOD of Cremnoceramus walterdorfensis walterdorfensis of the inoceramid group, whereas the base of the Santonian stage was determined using the LOD of Dicarinella primitiva of the Whiteinellids group and the FODs of Dicarinella asymetrica and Inoceramus aff. vistulensis (an inoceramid species). The FODs of Globotruncanita elevata and Ventilabrella austiniana, along with the extinction of the Marginotruncanid group, were used to identify the base of the Campanian stage in the Shorab section.

Fossil echinoid (Echinoidea, Echinodermata) diversity of the Early Cretaceous (Hauterivian) in the Paris Basin (France)

This dataset inventories occurrence records of fossil echinoid specimens collected in the Calcaires à Spatangues Formation (CSF) that crops out in the southeast of the Paris Basin (France), and is dated from the Acanthodiscus radiatus chronozone (ca. 132 Ma, early Hauterivian, Early Cretaceous). Fossil richness and abundance of the CSF has attracted the attention of palaeontologists since the middle of the nineteenth century. This dataset compiles occurrence data (referenced by locality names and geographic coordinates with decimal numbers) of fossil echinoids both collated from the literature published over a century and a half, and completed by data from collection specimens. The dataset also gives information on taxonomy (from species to order and higher taxonomic levels), which has been checked for reliability and consistency. It compiles a total of 628 georeferenced occurrence data of 26 echinoid species represented by 22 genera, 14 families, and 9 orders.

Echinoids of the Genus Tetragramma Agassiz (Phymosomatoida) from the Aptian Sediments of the Basab Region, Northwest of Kerman, Iran

The echinoid fauna of Basab area (Aptian), northwest of Kerman, is fairly rich and diverse, represented by Pygaulidae, Acropeltidae, Emiratiidae, Toxasteridae, Holectypidae, Stomechinidae and Saleniidae. Four regular echinoid species, among which three are new, assigned to genus Tetragramma Agassiz, are described and illustrated in the present paper. The new species are Tetragramma basabensis, T. depressum and T. tetratuberculatus. The diagnostic features of the species are chiefly the number of interambulacral tubercles on ambital plates, the size of apical disc and peristome, and also horizontal and vertical outlines of the test. The Tetragramma specimens occur in association with a rich orbitolinid fauna and macro-invertebrates consisting of bivalves, brachiopods, corals and gastropods. Associated micro-macro fauna suggest an Aptian age for the sediments.

Marine diversity in the geological record and its relationship to surviving bedrock area, lithofacies diversity, and original marine shelf area

Biological principles suggest that recorded species diversity should increase as sampled area and habitat diversity increase. However, the interactions between Earth system drivers of these physical quantities, their representation in the preserved rock record, and fossil species counts are debated. We tracked marine bedrock area, lithofacies diversity, and echinoid species diversity through an 80 m.y. sea-level cycle, as recorded in the Cretaceous of the United Kingdom, to test these relationships. Relative completeness of the rock record rises during transgression but drops rapidly at maximum flooding and continues to fall during highstand. Lithofacies diversity peaks during transgression but drops sharply as maximum flooding is reached, whereas bedrock area peaks at maximum flooding then declines progressively through the highstand interval as a result of post-Cretaceous erosion. Both bedrock area and number of lithofacies units correlate with species diversity, but species diversity is predicted best by the two combined. There are no simple relationships between bedrock area and lithofacies diversity or the original area of marine sediments and range of habitats that once existed; these variables are strongly shaped by stratigraphic architecture. While the geological record left by a major sea-level cycle accurately captures the biological evolution of local communities, it is incomplete and systematically biased in its coverage of environments and communities. Erosional truncation of sediment packages and species ranges in the later stages of sea-level cycles explains the reported asymmetric relationship between macroevolution and macrostratigraphy.

Bathyal sea urchins of the Bahamas, with notes on covering behavior in deep sea echinoids (Echinodermata: Echinoidea)

In a survey of the bathyal echinoderms of the Bahama Islands region using manned submersibles, approximately 200 species of echinoderms were encountered and documented; 33 species were echinoids, most of them widespread in the general Caribbean area. Three species were found to exhibit covering behavior, the piling of debris on the upper surface of the body. Active covering is common in at least 20 species of shallow-water echinoids, but it has been reliably documented previously only once in deep-sea habitats. Images of covered deep-sea species, and other species of related interest, are provided. Some of the reasons adduced in the past for covering in shallow-water species, such as reduction of incident light intensity, physical camouflage, ballast in turbulent water, protection from desiccation, presumably do not apply in bathyal species. The main reasons for covering in deep, dark, environments are as yet unknown. Some covering behavior in the deep sea may be related to protection of the genital pores, ocular plates, or madreporite. Covering in some deep-sea species may also be merely a tactile reflex action, as some authors have suggested for shallow-water species.

The new list of shallow water echinoids (Echinodermata: Echinoidea) for Puerto Rico

We present here the most updated list of sea urchins for Puerto Rico. We report, for the first time, the occurrence of the irregular echinoids Paraster floridiensis and Clypeaster subdepressus for the island. These reports increase the number of shallow water echinoid species for Puerto Ricoto to 19 and expand the known regional distribution range for both species.

Direct relationship between osmotic and ionic conforming behavior and tissue water regulatory capacity in echinoids

Echinoderms are considered marine osmoconforming invertebrates. However, many are intertidal or live next to estuaries, tolerating salinity changes and showing extracellular gradients to dilute seawater. Three species of echinoids – Lytechinus variegatus, which can occur next to estuarine areas, the rocky intertidal Echinometra lucunter, and the mostly subtidal Arbacia lixula – were submitted to a protocol of stepwise (rate of 2–3psu/h) dilution, down to 15psu, or concentration, up to 45psu, of control seawater (35psu). Coelomic fluid samples were obtained every hour. The seawater dilution experiment lasted 8h, while the seawater concentration experiment lasted 6h. Significant gradients (40–90% above value in 15psu seawater) for osmolality, sodium, magnesium, and potassium were shown by L. variegatus and E. lucunter. A. lixula showed the smallest gradients, displaying the strongest conforming behavior. The esophagus of the three species was challenged in vitro with 20 and 50% osmotic shocks (hypo- and hyperosmotic). A. lixula, the most “conforming” species, showed the highest capacity to avoid swelling of its tissues upon the −50% hyposmotic shock, and was also the species less affected by salinity changes concerning the observation of spines and ambulacral feet movement in the whole-animal experiments. Thus, the most conforming species (A. lixula) displayed the highest capacity to regulate tissue water/volume, and was also the most euryhaline among the three studied species. In addition, tissues from all three species swelled much more than they shrank under osmotic shocks of same magnitude. This distinct trend to gain water, despite the capacity to hold some gradients upon seawater dilution, helps to explain why echinoderms cannot be fully estuarine, or ever enter fresh water.

<strong>Broad application of non-invasive imaging techniques to echinoids and other echinoderm taxa*</strong>

Tomographic imaging techniques such as micro-computed tomography (μCT) and magnetic resonance imaging (MRI) permit the gathering of digital anatomical data from whole animal specimens non-invasively. The resulting datasets can be used for direct observation of the two-dimensional tomographic image data as well as for manual and semi-automated three-dimensional modelling. Freshly fixed specimens as well as preserved museum material can be successfully ana­lyzed using this approach, giving the zoomorphologist a powerful tool for large-scale comparative studies. In order to demonstrate the principle suitability of non-invasive imaging in echinoderm research, μCT scans of 199 and MRI scans of 92 sea urchin (Echinodermata: Echinoidea) species were acquired, resulting in a total of 203 analyzed echinoid species. The taxa selected represent 50 of the currently recognized 60 extant sea urchin families. The present article lists all spe­cies that have been analyzed so far and provides information about the scanning parameters employed for each dataset. Furthermore, the workflow established to generate three-dimensional models of sea urchins is outlined. Using a number of examples from μCT as well as MRI scans performed on echinoids, the potential of the systematic approach described here is highlighted. Finally, the suitability of non-invasive imaging techniques for the study of other echinoderm taxa is assessed based on multimodal datasets of representative species.

Description of two new fossil echinoids (Echinodermata: Echinoidea) from the Early Hauterivian (Early Cretaceous) of the Paris Basin (France)

Two new echinoid genera and species, Salvaster roberti gen. et sp. nov. and Pygolampas edita gen. et sp. nov. are de-scribed. They were collected in the Calcaires à Spatangues Formation (CSF) that consists of limestone and clay sedimentsdeposited in the southeast of the Paris Basin (France) during the Early Hauterivian (Early Cretaceous). The CSF is datedfrom the Acanthodiscus radiatus chronozone, a time-interval of overall high sea level in Western Europe, but it yields arich shallow-water fossil fauna mostly represented by benthic invertebrates. Of the 54 echinoid species ever described inthe CSF, 26 species are recognized here. They are distributed into 16 different families, among which regular (13 species)and irregular (13 species) echinoids are represented in equal proportion. This work confirms the high level of echinoid diversity in the CSF for that time-period.

Evidence for the bioerosion of deep-water corals by echinoids in the Northeast Atlantic

In situ video observations of echinoids interacting with deep-sea coral are common in the deep-sea, but paradoxically the deep-sea literature is devoid of reports of bioerosion by extant echinoids. Here we present evidence of contemporary bioerosion of cold-water coral by four species of deep-sea echinoids, Gracilechinus elegans, Gracilechinus alexandri, Cidaris cidaris, and Araeosoma fenestratum, showing that they actively predate on the living framework of reef building corals, Lophelia pertusa and Madrepora oculata, in the NE Atlantic. Echinoid specimens were collected in six canyons located in the Bay of Biscay, France and two canyons on the north side of the Porcupine Bank and Goban Spur, Ireland. A total of 44 live specimens from the four taxa (9 of G. elegans, 4 of G. alexandri, 21 of C. cidaris and 10 of A. fenestratum) showed recent ingestion of the coral infrastructure. Upon dissection, live coral skeleton was observed encased in a thick mucus layer within the gastrointestinal tract of G. elegans and G. alexandri while both live and dead coral fragments were found in C. cidaris and A. fenestratum. Echinoid bioerosion limits the growth of shallow-water reefs. Our observations suggest that echinoids may also play an important role in the ecology of deep-water coral reefs.

Fertilisation, embryogenesis and larval development in the tropical intertidal sand dollar Arachnoides placenta in response to reduced seawater pH

We examined the response of the tropical sand dollar Arachnoides placenta to reduced seawater pH in experiments spanning ca. 50 % of the planktonic larval duration. A. placenta inhabits intertidal sandy beaches where we observed a minimum in situ pH range 0.06 pH units (pH 8.10–8.16). The responses of gametes and larvae to seawater pH were tested in vitro in ambient (pH 8.14, pCO2 = 525.7 μatm, total alkalinity = 2,651 μmol kg soln−1) and three reduced pH seawater treatments (7.8–7.0). Percentage fertilisation decreased significantly with decreasing pH across a range of sperm/egg ratios (4:1 up to 4,000:1). A. placenta reached the advanced pluteus stage in 4 days, and during this time, we saw no difference in survival rate of larvae between the ambient (67 %) and pH 7.79 (72 %) treatments. Four-day survival was, however, reduced to 44 and 11 % in the pH 7.65 and 7.12 treatments, respectively. Larval development and morphometrics varied among pH treatments. Embryos reared in pH 7.12 exhibited arrested development. Larvae reared at pH 7.65 showed delayed development and greater mortality compared with those reared at pH 7.79 and 8.14. When larval morphometrics are compared among larvae of the same size, differences in larval width and total arm length between pH treatments disappear. These results suggest that variation in larval size among the three highest pH treatments at a given time are likely the result of slower development and apparent shrinkage of surviving larvae and not direct changes in larval shape. There were no differences in the percentage inorganic content (a proxy for calcification) in larvae reared in either an ambient or a pH 7.7 treatment. The responses of fertilisation and development to decreased pH/increased pCO2 in A. placenta are within the range of those reported for other intertidal and subtidal echinoid species from colder latitudes.