Echinoid Species Research Articles

Uses and limitations ofactuopalaeontological investigations on echinoids

The study of recent echinoids from the Red Sea has shown that actuopalaeontological investigations have importantimplications for at least two major aspects of palaeonenvironmental interpretations: 1) taphonomic processes and 2) the distribution of sea urchins with respect to environmental parameters. An important aspect of actuopalaeontological studies based on experimental as well as field observations, concerns taphonomic processes. It can be shown that a number of agents including predation, transport, encrustation etc. differentially affect the fossilization potential of echinoid species. The extent of these processes are both facies dependent as well being influenced by the inherent skeletal properties of the echinoid skeleton. The distribution of echinoids is controlled by a number of environmental factors including substrate characteristics, nutrient supply, and exposure to differential current conditions. Actuopalaeontological studies can elucidate these dependencies especially in conjunction with detailed facies and sediment analyses. The distributions of irregular echinoids are shown to be tightly constrained by grain size characteristics of the sediment. Cryptic habitats and patchy distributions lead to difficulties in quantifying living echinoids over large areas. The instability of the echinoid test complicates the comparison of echinoid biocoenosis and taphocoenosis. These problems are seen to constitute the main limits of actuopalaeontological investigations.

Functional Consequences of Phenotypic Plasticity in Echinoid Larvae.

Phenotypic plasticity in feeding structures has been described for several larvae of marine invertebrates, including four species of echinoids. In these echinoids, larvae grown with scarce food grow a longer ciliated band than larvae grown with abundant food. Such phenotypic plasticity may be functionally significant if longer ciliated bands permit higher feeding rates when food is scarce. We replicate an earlier result showing that larvae of a sand dollar, Dendraster excentricus, grow longer ciliated bands in culture with scarce food. We show that these larvae can capture suspended food particles at the tips of longer arms, and that longer ciliated bands result in higher maximum clearance rates. The maximum clearance rate is enhanced by this phenotypic plasticity both early and late in larval life. However, longer ciliated bands did not completely compensate for reduced food supply: larvae grown with scarce food needed more time to complete larval development and metamorphosed into smaller juvenile sand dollars relative to larvae grown with abundant food.

Effects of food diet on the survival, development and growth rates of two cultured echinoplutei (Paracentrotus lividusandArbacia lixula)

Summary We examined the effects of phytoplanktonic food on the survival rate, growth, development, length of larval life and competence for metamorphosis for two species of echinoids from the northeastern part of the western Mediterranean Sea. For larvae of Arbacia lixula seven diets were tested and for those of Paracentrotus lividus two. A diet of Cricosphaera elongata yielded a high survival rate (80%) and rapid larval growth; development was shorter, rudiment diameter was larger and metamorphosis rate was higher. There was a maximum feeding level beyond which no change in growth and development rate was observed. In response to a poor diet, larvae increased the larval period and the length of the larval arms; the survival rate decreased and development was slow and more variable. However, there was no change in the post-larval diameter regardless of diet history.

Intraskeletal Matrix Proteins in Echinodermata

An intraskeletal soluble matrix protein of 83 kD was isolated from the calcareous skeletal elements of living specimens of two asteroid species, one echinoid species, and an early Pleistocene fossil specimen of an extant echinoid species. Characterization of this protein by sodium dodecyl sulphate - polyacrylamide gel electrophoresis, reverse phase liquid chromatography, and amino acid composition analysis confirms its similarity to matrix proteins from other phyla. It is composed of a relatively high percentage of the acidic amino acids especially aspartic acid. The 83 kD protein stains only faintly with silver stain and not at all with Coomassie blue, as is typical of matrix proteins. As this protein occurs in both living and fossil echinoids, its analysis may provide information about phylogenetic relations.

Reproduction in marine invertebrates in “stable” environments: the deep sea model

Summary Studies over the last 15 years have revealed that deep-sea benthic megainvertebrates show a variety of reproductive patterns that are adapted to the deep-sea, an environment in which the fauna occurs at low densities and resources are sparse. In the NE Atlantic the majority of species reproduce year round whilst a limited number of species reproduce on a seasonal basis believed to be entrained by the deposition of surface derived organic material on the deep-sea bed. A third pattern of rapid growth and early reproduction is found in a limited number of species that utilize unpredictable and ephemeral resources in the deep sea. Examination of the fertilization and behavioural biology of species from the bathyal depths suggest some species enhance fertilization success by forming pairs during their breeding season. However, the same concentration of sperm, as seen in shallow water invertebrates, is required for successful fertilization. At least one deep-sea species of echinoid requires high pressur...

GAMETE COMPATIBILITY OR INCOMPATIBILITY? A COMMENT ON LESSIOS AND CUNNINGHAM (1990).

GAMETE COMPATIBILITY OR INCOMPATIBILITY? A COMMENT ON LESSIOS AND CUNNINGHAM (1990).

A new genus and species of regular echinoid from the Late Cretaceous of Gebel El Rowdah, Hatta area, Oman-U.A.E.

This paper is the fourth in a continuing series describing Late Cretaceous echinoids from the United Arab Emirates (Ali, 1989, 1990, in press). A single semi-spherical Arbaciidae was discovered while I was preparing my earlier paper on additional echinoids of Gebel El Rowdah. This specimen resembled Codiopsis L. Agassiz (1840), but differs in having the ambulacral and interambulacral tubercles developed throughout the adapical and adoral sides. The ambulacral structure in the new genus is also unique among arbaciids. Therefore, the specimen is here placed in a new genus, having been omitted from previous papers because of the paucity of the material. Recently, during a field trip with students of the Geology Department, U.A.E. University, to the same location visited in December 1990, an additional 18 specimens were collected. These provide the basis for the present description of a new genus.

Transformation of algal turf by echinoids and scarid fishes on French Polynesian coral reefs

The respective roles of regular echinoids and scarid fishes in the transformation of turf algae, the main food resource for reef herbivores, were investigated on French Polynesian coral reefs. The role of one species of parrotfish (Scarus sordidus) was compared with that of four species of echinoids. The degree and ways of degradation of the algal matter were determined by the organic matter percentage, the composition of the sugar fraction, and the concentration and composition of chlorophylltype pigments as assayed by HPLC analysis. Chemical analyses were performed on anterior and posterior intestines for scarids, intestinal contents and faeces for echinoids, and on fresh algal turf as a control of initial food quality. A decrease in mean percentage of organic matter in gut content was observed from intestine (9.7%) to faeces (7%) in sea urchins, but not in parrotfishes. The total sugar fraction decreased from fresh algal turf (32% of total organic matter) to echinoid (28%) to scarid (18%) gut contents. The ratio of insoluble to soluble sugars (I/S ratios) was higher in echinoids (2.6) than in scarid gut contents (1.0). A decrease in the total pigment concentration was measured from fresh algal turf to echinoid and it was found to be even lower in scarid gut contents. Chromatograms showed that the composition of chlorophyll-type pigments in scarid intestines was very similar to fresh algal turf, with a dominance of native forms, mainly chlorophyll a and b. On the contrary, degraded pigment forms dominated in echinoids. The main degraded products were pheophorbides in sea urchins, and chlorophyllides in parrotfishes. These results provided evidence for differentiation in digestive processes occurring in the two types of grazers. Echinoids released higher degraded algal material than did scarids. Thus, these two types of grazers play different roles in the recycling of organic matter on coral reefs.

Developmental Expression of Echinonectin, an Endogenous Lectin of the Sea Urchin Embryo.

Echinonectin (EN) is a galactose-binding lectin present in eggs and embryos of the sea urchin Lytechinus variegatus. Recent studies have suggested that EN is a hyaline layer protein that may function as a substrate adhesion molecule (SAM) during development. We have used monoclonal and affinity-purified polyclonal antibodies that specifically recognize this protein to determine its spatial and temporal expression during embryogenesis. EN is stored in granules or vesicles in the unfertilized egg. After fertilization, these granules are rapidly redistributed to the apical cytoplasm of the zygote. Our results show that at subsequent stages of development the lectin is expressed by cells of all three germ layers, including cells of the developing gut, coelomic pouches, and ectoderm, and by both primary and secondary mesenchyme cells. In contrast to previous observations based solely upon light level immunofluorescent staining, immunoelectron microscopy demonstrates that EN is localized in intracellular, membrane-bounded vesicles. In epithelial cell types these vesicles have a highly polarized distribution and are found in the apical cortical cytoplasm. In mesenchyme cells the distribution of EN-containing vesicles is not obviously polarized. Steady-state levels of EN protein in the embryo remain almost constant from fertilization to the pluteus larva stage, Metabolic labeling studies show that synthesis of EN in L. variegatus begins immediately after fertilization and continues throughout embryogenesis. Monospecific antibodies raised against L. variegatus EN have also been used to determine whether this lectin is expressed in other echinoid species.

First Oligocene occurrence of the irregular echinoid Macropneustes mortoni (Conrad)

A nearly complete test and several test fragments of the irregular echinoid species Macropneustes mortoni (Conrad) were recently discovered in Lower Oligocene (Vicksburgian) strata of southern Alabama. To date, M. mortoni has only been reported from Upper Eocene (Jacksonian) sediments of Alabama, Georgia, and Florida (Cooke, 1959; Toulmin, 1977; Carter, 1987). This is one of the very few species of the diverse Eocene echinoid fauna of this region to survive the terminal Eocene extinctions.

The Development and Larval Form of an Echinothurioid Echinoid, Asthenosoma ijimai, Revisited.

The modified development from cleavage to late larval form of the echinothurioid echinoid, Asthenosoma ijimai, was re-examined using light microscopy and scanning electron microscopy of whole and sectioned stages. Although an original study (Amemiya and Tsuchiya, 1979) reported direct development without evidence of a pluteus larva, we found that the unusual development can be interpreted as a topologically reflected, reduced pluteus, with vestigial larval arms and a greatly reduced larval skeleton. This developmental pattern produces the third and most reduced pluteus form known among the six echinoid lineages with modified development that have been studied thus far. Features such as an equal fourth cleavage, extrusion of yolk into the blastocoel, and the presence of large numbers of cells within the blastocoel are convergent with traits reported for other species with modified development. Coelom formation is clearly modified from that of species with feeding larval development, but notably the hydrocoel begins to develop podial buds prior to separation from the archenteron. Echinothurioid sea urchins are considered to be the most primitive living euechinoids, and in A. ijimai the timing of mesenchyme cell ingression and the formation of epineural folds were similar to these features in other euechinoids. Indentation of the juvenile oral surface relatively late in larval development raises the possibility that the amniotic invagination (vestibule), common in all other euechinoids, may be a trait incorporated into the development of echinoids at the time of origin of the echinothurioids. The structural comparisons reported here show a need for further detailed morphological studies of developmental modifications in other echinoid species.

Presence and absence of monthly reproductive rhythms among eight Caribbean echinoids off the coast of Panama

Monthly reproductive rhythms of five species of regular and two species of irregular echinoids were studied in the San Blas Archipelago during 1984. The annual reproductive periodicity of these species had been studied at the same locality in 1982–83. The data were subjected to Rayleigh's tests, autocorrelation analysis, and cross correlation analysis with the phases of the moon. Previously published data for an additional species, Diadema antillarum, that had been studied with the same sampling regime during the same time period in the same area, were re-analysed with the statistical procedures used in this paper. The eight species could be classified in four categories with regards to their mode of spawning: (1) Tripneustes ventricosus (Lamarck), Echinometra viridis A. Agassiz and Leodia sexiesperforata (Leske) spawn at random during the lunar cycle. (2) Clypeaster rosaceus (Linnaeus) and Lytechinus williamsi Chesher show nonrandom distributions of their spawning activity around the lunar cycle, but do not appear to follow any lunar periodicity. (3) Eucidaris tribuloides (Lamarck) and Diadema antillarum Philippi have a lunar rhythm in their reproduction, each spawning during a different lunar phase. (4) Lytechinus variegatus (Lamarck) follows a semilunar cycle, spawning every new and full moon, a pattern that had also been found in Bermuda in 1938. The phylogenetic position of the eight species indicates that lunar periodicity is not a lineage-specific trait, inherited from a common ancestor. It must, instead, have evolved independently in different echinoid taxa, possibly as an adaptation to serve the reproductive requirements of each species. However, attempts to identify its adaptive significance through comparisons between the species failed to support any of the hypotheses examined. Because water level on the Atlantic coast of Panama is determined by meteorological conditions as well as base tides, lunar spawning is unlikely to be cued by the tide, or to be an adaptation for flushing of fertilized zygotes away from reefs. Species in which lunar rhythms are present are not distinguished from species that spawn at random by their special photosensitivity, they are unlikely to be doing so because of food limitations during part of the month, and they do not appear to be under stronger selection for reproductive synchrony than species that have no lunar rhythms.

Lateral variations of size‐frequency distribution in a fossil echinoid community and their palaeoecological significance

The analysis of size-frequency spatial distribution of three species of Cenomanian echinoids in a single fossil assemblage shows both intraspecific and interspecific horizontal segregation of the individuals parallel to the variations in silt and organic matter levels of the substrate. The exceptional preservation of echinoids. fossilized in the living position with part of their spines. and their multimodal size-frequency distribution, with no evidence of physical transportation. suggest that a catastrophic event resulted in the fossilization of the demographic structure of the populations. The assemblage. being the result of mass mortality of a community, corresponds to a census assemblage. Thus the patchy segregation of echinoids could not primarily be influenced by size-selective taphonomy (current winnowing, biological or mechanical destruction) but more likely determined by biological phcnomena like mortality and recruitment patterns, high juvenile growth, substrate selection and herd mode of life. Recent examples of spatial separation of adults and juveniles. given for different species of echinoids. show that these patchy distributions are widespread, and therefore may be a privileged source of fossil preservation of cohort's size-frequency distribution in catastrophic mortality. □Palaeoecology, size-frequency distribution, demography, echinoids. spatangoids, cassiduloids, Mecaster, Catopygus, Nucleopygus.

Biochemical and energetic composition of bathyal echinoids and an asteroid, holothuroid and crinoid from the Bahamas

The biochemical and energetic composition of body components of ten species of bathyal echinoids, and an asteroid, a holothuroid and a stalked crinoid were determined from individuals sampled from a variety of deep-water sites near the Bahamas (north Caribbean Sea) in October 1988. When compared with other studies of echinoderms, no geographic- or depth-related differences in biochemical or energetic composition were found. Body-wall tissues were composed primarily of skeletal material (mineral ash), but were comparatively high in organic material in the echinothuriid echinoids, and the asteroid and holothuroid. Gut tissues and pyloric cecae had high levels of lipid and protein, indicating their potential role in nutrient storage. Body-wall tissues were generally low in energy, but were highest in the echinoidsAraeosoma belli (7.7 kJ g−1 dry wt) andSperosoma antillense (8.0 kJ g−1 dry wt), the asteroidOphidiaster alexandri (8.9 kJ g−1 dry wt), and the holothuroidEostichopus regalis (13.1 kJ g−1 dry wt). Energy levels of gut and pyloric cecal tissues were two to three times higher than those of body-wall tissues. Total somatic tissue energy values varied greatly among species, ranging from 1.5 kJ in the echinoidAspidodiadema jacobyi to 142.1 kJ inE. regalis. As the bathyal echinoderms examined in this study occur in great abundance, they represent a significant reservoir of organic and inorganic materials and energy in deep-water benthic systems.

Late Eocene Echinoid Biofacies of Florida

Combining the substrate preferences of Jacksonian (late Eocene) echinoid species of Florida (Carter et al., 1989) with their geographic distributions (Carter, 1987a) allows construction of biofacies maps reflecting the spatial distribution of carbonate mud-rich and carbonate sand-rich sediments in the Ocala Group of Florida. Both cluster analysis and interpretation of individual localities suggest a consistently sandy bottom over most of the shelf in the early Jacksonian, with a north-south gradient developing during the middle and late Jacksonian. In the middle Ocala, some mud-tolerant species are present in the northern part of the Florida peninsula, toward the Suwannee Strait, and the middle Ocala of the western panhandle is dominated by mud-tolerant species. In the upper Ocala, most localities contain a significant proportion of mud-dwelling species, and the northward prevalence of mud-tolerant assemblages is even more pronounced, with those assemblages closer to the Suwannee Strait entirely dominated by mud-dwellers. These data suggest that the Ocala Bank of Cheetham (1963) was more of a northward sloping carbonate ramp than a carbonate shelf.

Cenomanian echinoids, larger foraminifera and calcareous algae from the Natih Formation, central Oman Mountains

Within the Natih Formation (late Albian-early Turonian) of the Oman Mountains, there occurs a distinctive, correlatable horizon with an abundant and moderately diverse echinoderm fauna. This horizon occurs within Member c of the Natih Formation and can be assigned a latest middle Cenomanian age based on the associated microfossil assemblage which is dominated by alveolinids and gymnocodiacian algae. The depositional environment of this echinoderm-rich bed was probably back barrier, close to radiolitid rudist biostromes and bioclastic shoals which fringed the upper Natih shelf edge. Nine species of echinoid are described, most of which are new records for the Arabian Peninsula. One new species, Pedinopsis sphaerica , is erected. Coenholectypus larteti dominates the assemblage and occurs together with Stereocidaris sarracenarum, Tetragramma variolare, Heterodiadema lybica, Pedinopsis humei, P. desori, P. sphaerica, Hemiaster syriacus and H. cubicus . The composition of the genus Pedinopsis is critically reviewed and a new subgenus, Sinaiopsis , erected. Many of the species have previously been reported from Egypt, the Sinai Peninsula and Israel.

Atelostomatid sea urchins from Australian and New Zealand waters (Echinoidea : Cassiduloida, Holasteroida, Spatangoida, Neoplampadoida)

The systematics and distribution of 28 species (17 genera) of atelostomatid echinoids from the seas around Australia and New Zealand are discussed. Eighteen species are new to the region. A new genus, Acanthotrema, Family Asterostomidae, is described, and new species are assigned to the genera Gymnopatagus, Eupatagus, Metalia, Spatagobrissus and Heterobrissus (2). Three species of Spatangus, S. pallidus H. L. Clark, S. thor Fell and S. beryl Fell, are synonymised with S. Iutkeni A. Agassiz. Paramaretia multituberculata Mortensen is synonymised with P. peloria H. L. Clark. A checklist of Australasian atelostomatid echinoids, giving a distributional summary, is provided.

Adaptation and Phylogeny as Determinants of Egg Size in Echinoderms from the Two Sides of the Isthmus of Panama

Theoretical models and empirical observations have attempted to determine selective pressures that influence the egg size of marine invertebrates. Both approaches generally assume that egg size is free to evolve toward an evolutionarily stable point without any constraints imposed by phylogeny. The size of eggs in 22 species of echinoids and 2 species of asteroids from the two sides of the Isthmus of Panama was determined in an effort to assess the rate at which differences between species can accumulate. Of these 24 species, 14 belong to pairs of geminate species, presumed to have been divided by the rise of the isthmus 3.1-3.5 million years ago. Comparisons between egg size in related species evolving in separate environments for the same period of time, and in related and unrelated species living in the same environment, were used to evaluate the relative importance of adaptation and phylogeny in determining the egg size of a species. In 12 of 13 comparisons, the mean egg size of each species was signi...

Modified Sperm Ultrastructure in Four Species of Soft-Bodied Echinoids (Echinodermata: Echinothuriidae) From the Bathyal Zone of the Deep Sea

Sperm of the bathyal echinothuriid echi noids Phormosomaplacenta, Sperosoma antillense, Ara eosomaftnestratum, and A. beii are similar to those of other echinoids, but have several unique morphological features involving the acrosomal vesicle, the nucleus, and the middlepiece. The acrosomal vesicle shows re gional staining differences including a densely staining central region surrounded by an electron-opaque corn ponent. Sperm nuclei are highly elongated and abruptly taper posteriorly. With the exception of one species, the nuclei lack a distinct centriolar fossa. Intracellular drop lets resembling lipid extend from the extreme posterior region of the middlepiece to form a collar around the proximal portion ofthe axoneme. The presence of lipid like bodies in the middlepiece suggest that the sperm are long-lived and therefore require additional energy stores not found in most metazoan sperm. These findings are compared with a similar study of sperm ultrastructure in three shallow-water echinothuriid species, and their potential significance is discussed in relation to the pres ent knowledge ofechinothuriid reproductive biology.

Toxicity of shallow-water Antarctic echinoderms

The toxicity of 23 species of shallow-water antarctic echinoderms from McMurdo Sound was investigated using Gambusia affinis (Vertebrata: Pisces) as a test organism. Ichthyotoxicity assays were conducted on the body wall tissues of thirteen species of asteroids and three species of holothuroids, the tests of three species of echinoids and the arms of three species of ophiuroids and one species of crinoid. Patterns of toxicity were class-specific, with varying degrees of toxicity occurring exclusively among the Asteroidea and Holothuroidea. Seven of the thirteen species of asteroids were mildly to highly toxic (54%), while one of the three holothuroids was mildly and one highly toxic. Toxicity was not related to the level of calcification of the body wall and energy level in asteroids. The only armored asteroid, Notasterias armata, was non-toxic. The occurrence of toxins in the body tissues of antarctic echinoderms is similar in pattern and frequency with that of temperate and tropical species.