Echinoid Species Research Articles

Biogeography and diversity of South Atlantic Cretaceous echinoids: implications for circulation patterns

This survey of echinoid species living on the African and South American margins of the South Atlantic Ocean in Cretaceous times is based on a review of published species and abundant unpublished material. The synthetic approach is used to ascertain how the South Atlantic was colonised by echinoids from the time it first opened in the Early Cretaceous until communications were established with the North Atlantic and Mediterranean–Tethys in the Late Cretaceous. The survey focuses on the biogeographical origin of immigrant species and their relations with Indo-Madagascan, North Atlantic and Mediterranean–Tethyan faunas. Qualitative variations in species diversity are also studied where available fossil material permits, together with the in situ evolution of certain lineages and their endemism. Finally, echinoid colonisation of the South Atlantic during the Cretaceous is viewed against palaeocurrent patterns. The survey shows, within the limits of material available, that no echinoid fauna attests to the existence of the narrow marine trough separating South America and Africa in the Barremian. In the Aptian, West African echinoids display a Mediterranean–Tethyan influence, indicating a probable link between south-east and west of Africa via the strait opened between Africa and Madagascar. Echinoid fauna on the Brazilian margin includes species found in what is now continental North America and on the Pacific seaboard of South America. During the Albian, South America separated completely from Africa and normal marine communications were established with the Western Tethys to the north and the Southern Ocean domain to the south. The echinoid fauna of the South Atlantic during the Albian and early Cenomanian was particularly rich and diversified, with the earliest ubiquitous species on both margins of the ocean. In the late Cenomanian–early Turonian, a Tethys–South Atlantic Ocean link probably formed in West Africa through the Sahara and Nigeria, favouring the influx of Mediterranean–Tethyan species to the South Atlantic. During the mid Turonian–Coniacian, the trans-Saharan channel closed, slowing down colonisation of the South Atlantic by Mediterranean–Tethyan echinoids, as the only connection was via the Central Atlantic. This period was marked by the stability of a number of lineages that survived without major morphological changes in areas colonised during Cenomanian times. In the late Senonian, the South Atlantic was largely open to the neighbouring ocean domains and a new trans-Saharan channel linked the Mediterranean–Tethys and South Atlantic directly. This allowed substantial faunal exchanges and most Senonian echinoids found on the South Atlantic rim are common to both its eastern and western margins.

Upper Cretaceous echinoids from James Ross Basin, Antarctica

New palaeontological collections made from Upper Cretaceous strata exposed within the James RossBasin, Antarctica, include ten echinoid species. Five species are described for the first time from Antarctica, while four others, previously published by Lambert in 1910, are revised according to the new data. The described echinoids comprise two new species, Huttonechinus antarctica nov. sp. and Nordenskjoeldaster? australis nov. sp., specimens closely related to an European spatangoid, Micraster aff. regularis, and three taxa that cannot be named at the specific level owing to poor preservation. In total, the fauna comprises three species of regular echinoids, five holasteroids, and two spatangoids. The ten taxa range in age from Santonian to Early Maastrichtian. The richest faunas are those associated with the prolific Gunnarites antarcticus ammonite assemblage. Several forms show affinities with Australia, New Zealand, south-east Africa and South America. There are indications that this is an essentially deep shelf echinoid fauna.

Evolution of sea urchin retroviral-like (SURL) elements: evidence from 40 echinoid species.

We conducted a phylogenetic survey of sea urchin retroviral-like (SURL) retrotransposable elements in 33 species of the class Echinoidea (sea urchins, sand dollars, and heart urchins). A 263-bp fragment from the coding region of the reverse transcriptase (RT) gene was amplified, cloned, and sequenced. Phylogenetic relationships of the elements isolated from independent clones, along with those from seven additional echinoid species obtained earlier by Springer et al., were compared with host phylogeny. Vertical transmission and the presence of paralogous sequences that diverged prior to host speciation can explain most of the phylogenetic relationships among SURL elements. Rates of evolution were estimated from cases in which SURL and host phylogenies were concordant. In agreement with conclusions reached previously by Springer et al., average rates of synonymous substitution were comparable with those of single-copy sea urchin DNA. High ratios of synonymous to nonsynonymous substitution suggest that the RT of the elements is under strong purifying selection. However, a high proportion (approximately 15%) of elements with deleterious frameshifts and stop codons and an increase of the ratio of synonymous to nonsynonymous substitutions with divergence time show that in the short term this selection is relaxed. Despite the predominance of vertical transmission, sequence similarity of 83%-94% for SURL elements from hosts that have been separated for 200 Myr suggests four cases of apparent horizontal transfer between the ancestors of the extant echinoid species. In three additional cases, elements with identical RT sequences were found in sea urchin species separated for a minimum of 3 Myr. Thus, horizontal transfer plays a role in the evolution of this retrotransposon family.

Molecular Phylogenetic Analysis of Diverse Forms of Echinoderm Guanylyl Cyclases

We found many isoforms of membrane-bound guanylyl cyclase (membrane GC) in the gonads of several echinoid species including Hemicentrotus pulcherrimus (six isoforms), Glyptocidaris crenularis (four isoforms), Clypeaster japonicus (three isoforms), Diadema setosum (three isoforms), and Brissus agassizii (three isoforms). In addition to these membrane GC isoforms, several putative soluble GC isoforms were also found, one in H. pulcherrimus, two in G. crenularis, and three in D. setosum. Other echinoderm species also possess many GC isoforms in their gonads: the starfish, Asterina pectinifera, has five membrane GC isoforms; the brittle star, Ophioplocus japonicus, possesses six membrane and two putative soluble GC isoforms; and the sea cucumber, Stichopus japonicus, contains five membrane and two putative soluble GC isoforms. We also obtained the full-length cDNA sequence of some of these isoforms, one for sperm-activating peptide (SAP) receptor-type GC, and the other for a homolog of the vertebrate natriuretic peptide receptors/membrane GCs, and analyzed their phylogenetic relationship among various invertebrate and vertebrate GC isoforms.

Phylogenetic Relationships among Four Echinoids of the Family Cidaridae (Cidaroida) Based on Allozymes

The family Cidaridae of the order Cidaroida from Japanese waters includes four common echinoid species belonging to four different genera: Stereocidaris japonica, Eucidaris metularia, Prionocidaris baculosa, and Phyllacanthus dubius. Phylogenetic relationship among the four species were investigated by allozyme analysis. From the allozyme variation in 18 genetic loci, Nei's genetic distances between species were calculated. The genetic distances were higher than those observed between confamilial genera in many other echinoids, but comparable to those between different families. The result suggests that the four cidarids diverged in earlier time from one another and generally have older evolutionary origin than members of families of the orders Echinoida and Diadematoida. A molecular phylogenetic tree for the four cidarids indicated the following: (1) S. japonica and Pr. baculosa are the most closely related to each other and diverged later. (2) E. metularia is more closely related to the cluster of S. japonica and Pr. baculosa than Ph. dubius. (4) Ph. dubius is the most distant among four species and diverged first. These allozyme results are discussed through the comparison with other non-molecular evidence.

Stock Evaluation of Three Littoral Echinoid Species on the Catalan Coast North‐Western Mediterranean

Abstract. We estimated the abundances of the three common littoral echinoid species Paracentrotus lividus, Arbacia lixula and Sphaerechinus granularis in a littoral zone between 0 and 10m depth on the Catalan shores NE Spain. Densities of each species were estimated from a total number of 11 571× 1 m2 sampling units deployed at 152 sites along the 13 zones into which the coast was divided. The surface area available in each of these zones was estimated at the scale of the sampling unit 1 m2 taking into account the fractal dimension of the shore. The stocks individuals > 2cm test diameter of these species for the whole Catalan shore ≅ 300 km, straight‐line distance were estimated to be about 279.1 × 106 individuals for P. lividus, 28.9 × 106 individuals for A. lixula and 10.9 × 106 individuals for S. granularis. These sea‐urchins are key species in the regulation of algal communities and some of them P. lividus. S. granularis are of commercial interest. This information will provide a tool for the future monitoring and management of this resource, which now faces diverse pressures of human origin.

Mesodermal Cell Differentiation in Echinoid Embryos Derived from the Animal Cap Recombined with a Quartet of Micromeres

Mesodermal cell differentiation in echinoid embryos derived from the animal cap recombined with micromeres was examined. An animal cap consisting of mesomere-descendants was isolated from a 32-cell stage embryo, and recombined with a quartet of micromeres isolated from a 16-cell stage embryo. The recombined embryos were completely depleted of the progenitors of an archenteron, pigment cells, blastocoelar cells and muscle cells. Secondary mesenchyme-like cells (induced SMC) were released from the archenteron derived from the animal cap cells in the recombined embryos. Some induced SMC differentiated into pigment cells, confirming previous data for another echinoid species. Moreover, three different kinds of mesodermal cells-blastocoelar, muscle and coelomic pouch cells-were formed in the recombined larvae. Experiments using a fluorescent probe confirmed that the pigment, blastocoelar, muscle cells and cells in part of the coelomic pouches in the recombined larvae were derived from the animal cap mesomeres. These results indicated that the animal cap mesomere had the potential to differentiate through cell fate regulation into four mesodermal cell types-pigment, blastocoelar, muscle and coelomic pouch cells-.

Low densities of sea urchins influence the structure of algal assemblages in the western Mediterranean

Numerous studies of interactions between urchins and algae in temperate areas have shown an important structuring effect of sea urchin populations. These studies focused almost wholly on the effect of high urchin densities on laminarian forests. In contrast, algal communities below 5–6 m depth in the northwestern Mediterranean are characterised by low sea urchin densities (<5 ind m −2) and the absence of laminarian forests. No previous research has addressed sea urchin/algal interactions in this type of community. To determine the effect of the most abundant echinoid species, Paracentrotus lividus, on well-established algal communities in this area, we performed a removal–reintroduction experiment in rocky patches located between 13 and 16 m depth in the northwestern Mediterranean, where sea urchin densities ranged between 0.9 and 3.4 ind m −2. After 6 months, the cover of non-crustose algae was significantly higher in the plots from which sea urchins had been removed than in control plots (84 vs 67% cover). These removal plots reverted to their original state upon reintroduction of sea urchins. The non-crustose algae consisted of turfing and frondose forms, with the former representing some 70% of the non-crustose algal cover. Change in the cover of turfing algae was responsible for the significant increase in algal development in the sea urchin removal plots. The response of frondose algae to the treatment varied between algal species. It is concluded that grazing by P. lividus exerts a significant effect on habitat structure, even in communities with low sea urchin densities, such as those found in vast areas of the Mediterranean sublittoral.

Reproductive Isolation? Interannual Variability in the Timing of Reproduction in Sympatric Sea Urchins, Genus Pseudechinus

Reproductive cycles of 3 sympatric species of the echinoid genus Pseudechinus, found in southeastern New Zealand, were examined over 27 months from October 1989 to December 1991. Analysis of periodic changes in relative gonadal size was used to help define the reproductive cycle of each species. Although P. huttoni reproduced primarily during the early (austral) summers of 1990 and 1991 (December-January), mature gametes were present in the gonads throughout much of the year. Conversely, P. novaezealandiae reproduced primarily during the autumn and early winter (May-July). P. albocinctus had an extended reproductive period in 1990, which peaked in late spring/early summer (December-January), followed by a gradual spawn-out to late autumn (May-June). The pattern was different in 1991, with a secondary peak in reproductive potential noted in late autumn (June). For all 3 species, males tended to be competent to spawn gametes for a longer period than were females. These observations were all corroborated by analysis of changes in overall gonad histology and in the distribution of oocyte sizes in the ovaries of each species throughout the year. P. huttoni and P. novaezealandiae thus appeared to exhibit temporal reproductive isolation from each other. Intraspecific as well as interannual variability in the timing of reproduction, however, suggests that such temporal isolation may not always be complete. In contrast, P. albocinctus was not temporally isolated from either of its 2 sympatric congeners. These results were examined in the context of seasonally variable environmental conditions. Additional key words: Echinoidea, Echinodermata, El Ninio, hybridization, reproductive isolation The echinoid genus Pseudechinus (MORTENSEN 1921) comprises 11 species, of which 6 are endemic to New Zealand waters (McKnight 1969) and 3 cooccur throughout much of their range in southern New Zealand. P. albocinctus (HUTTON 1872), P. huttoni (BENHAM 1908), and P. novaezealandiae (MORTENSEN 1921) are restricted primarily to waters off southern North Island, South Island, and subantarctic islands south of mainland New Zealand (Mortensen 1943; McKnight 1969). All 3 species have been recorded in sympatry in nearshore waters off the southeast coast of South Island from Oamaru (North Otago) to Foveaux Strait. The presence of 2 or more closely related species living in sympatry provides an interesting situation: closely related species may have similar life histories, possibly sufficiently similar to allow them to interbreed. How is the genetic integrity of a species maina Author for correspondence. E-mail: dmcclary@unitec.ac.nz tained if hybridization with congeneric species can occur? Is it maintained? A number of isolating mechanisms have been suggested, including microhabitat separation (Nishihara et al. 1991), differences in reproductive periodicity (Pearse & Cameron 1991), and gametic incompatibility (Strathmann 1981; Lessios & Cunningham 1990; Palumbi & Metz 1991). As these mechanisms are not likely to result directly from selection (see Butlin 1987; Endler 1989), they may be applied equally to both conand hetero-specific fertilization events; we will refer to them as constraints on fertilization. While there are many reported instances of 2 species of closely related echinoids living in sympatry (Mayr 1954), the co-occurrence of 3 or more congeneric echinoid species is somewhat unusual. Where it does occur, differences in the timing and/or place of reproduction have usually been noted between the species. Temperate-water echinoids typically reproduce annually or biannually for a relatively short period of time (Lawrence 1987; Strathmann 1987). As well, reThis content downloaded from 207.46.13.115 on Sat, 08 Oct 2016 04:36:26 UTC All use subject to http://about.jstor.org/terms

Inferring substrate preferences from test morphology in echinoids, and interpreting spatial and temporal patterns of diversity

Preservational style of fossil echinoid tests allows assessment of the likelihood of post-mortem transport out of the preferred sediment type of the living echinoid. Sedimentologic study of the matrix of untransported specimens allows a check on functional morphologic inferences of the species' preferred sediment types. Functional morphologic analysis allows inference of a species preferred sediment type because the petals, fasciolaes, tubercles, ambulacral pores, ambulacral shape, and test profile control the echinoid's ability to burrow, and the grain size of sediment into which it is capable of doing so. Past studies have achieved better than 90% accuracy in predicting the grain size of thin sections of rocks containing echinoids, simply by interpretation of their functional morphology. Most mistaken predictions are attributable to species living in sediments that are less difficult to burrow in (sands) than those to which they are adapted (muds). Other species may live in sediments in which they are not well adapted by assuming an epifaunal mode of life.Relative proportions of species in an echinoid fauna preferring various sediment grain sizes, plotted for each of a number of localities, has proven useful in inferring generalized facies patterns within regions.Plots of temporal changes in echinoid species diversity through time correspond well to changes in proportions of species inferred to have preferred various substrate conditions, suggesting an environmental and taphonomic component to simple diversity curves.

Potential for deep sea invasion by Mediterranean shallow water echinoids:pressure and temperature as stage-specific dispersal barriers

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 154:197-209 (1997) - doi:10.3354/meps154197 Potential for deep sea invasion by Mediterranean shallow water echinoids: pressure and temperature as stage-specific dispersal barriers Young CM, Tyler PA, Fenaux L Hypotheses about the origin of the deep sea fauna often assume that the deep sea was first colonized by cold water animals migrating through isothermal water columns in polar seas. Deep water in the Mediterranean Sea has much warmer temperatures than comparable depths in the larger ocean basins. Moreover, the entire water column may be virtually isothermal during the winter months, making oceanographic conditions in the Mediterranean analogous to those prevailing throughout most of the world ocean during the Mesozoic and Cenozoic. We investigated the physiological potential for deep sea invasion through a warm water column by studying the pressure and temperature tolerances of embryos and larvae of 3 species of shallow water Mediterranean echinoids, Paracentrotus lividus, Arbacia lixula, and Sphaerechinus granularis. Early life history stages of all 3 species tolerated pressures (to 150 atm) much higher than those experienced in the adult environment. Cold temperatures (<10°C) exacerbated the adverse effects of pressure; larvae were more likely to survive at deep sea pressures and warm temperatures than at shallow water pressures and cold temperatures. Tolerances to high pressures and low temperatures increased with ontogeny and varied with species. In the Mediterranean, high pressures should be a more important limiting factor than low temperatures. Nevertheless, some species have physiological tolerances that should allow them to colonize bathyal depths. Absence of these shallow water species from such depths must be attributed to factors other than pressure and temperature. Mediterranean · Echinoids · Pressure · Barophysiology Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 154. Publication date: July 31, 1997 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1997 Inter-Research.

Spermiotoxicity and embryotoxicity of heavy metals in the echinoid Paracentrotus lividus

AbstractSpermio‐ and embryotoxicities of Cu, Ag, Cd, and Hg were investigated in Paracentrotus lividus, the dominant echinoid species of the Mediterranean. Spermiotoxicity was studied by assessing the effects of sperm exposure on fertilization rate (FR) as well as on the induction of transmissible damages to the offspring. Embryotoxicity was studied by assessing developmental defects in larvae exposed to the tested metals throughout their development. Sperm exposures resulted in significant decreases of FR, depending on both metal concentration and duration of the exposure. Lowest spermiotoxic concentrations recorded when sperm were exposed for 75 min to the metals were 10−7 M Hg(II), 10−6 M Ag(I), 10−5 M Cu(II), and 10−5 M Cd(II). Tested metals did not exert any transmissible damage to spermatozoa that could result in larval malformations in the offspring, even for concentrations that dramatically reduced FR. Single‐element exposures of embryos for 72 h resulted in developmental defects whose occurrence and severity showed a steep dose dependence, indicating that once a threshold is reached, any further increase in toxicant concentration rapidly enhances the impairment of target function(s). Those observations suggest the involvement of a saturable protective mechanism. Lowest observed embryotoxic concentrations of the metals were 10−7 M Hg(II), 2.5 × 10−7 M Ag(I), 5 × 10−7 M Cu(II), and 10−5 M Cd(II) and are in the range of concentrations reported in heavily polluted marine environments. Thus, the possibility of impairment of echinoid development actually exists in metal‐contaminated marine environments, possibly threatening echinoid populations in those environments.

Hybridization and introgression between Indo-Pacific species of Diadema

We present the first case of hybridization between echinoid species evaluated through genetic markers and morphology. We examined the three tropical Indo-Pacific species of the genus Diadema: D. paucispinum A. Agassiz, D. savignyi (Audouin) Michelin and D. setosum (Leske). Specimens morphologically intermediate between two of these species, D. savignyi and D. setosumhave previously been noted. Fertile hybrids have also been produced in the laboratory. To determine extent of hybridization, we first assayed the allozyme products of 22 loci in individuals which, on the basis of morphology and collection locality, could be unambiguously assigned to one of the three species. We found four loci that were either diagnostic or semi-diagnostic between D. setosum and the other two species, and one locus semi-diagnostic between D. savignyi and D. paucispinum.We then assayed individuals of intermediate morphology to find out whether they had hybrid genotypes. In the Ryukyu Islands, where D. setosum and D. savignyi coexist, we found one specimen which on the basis of all four diagnostic loci was an F1 hybrid, and several individuals that could be either F2 (or later-generation) hybrids or progeny of backcrosses.We also found one individual that on both genetic and morphological grounds appeared to belong to D. paucispinum (even though this spcies has only been reported from Hawaii and Kiribati) and three other individuals that carried alleles characteristic of D. paucispinum. Thus, previous reports of hybridization between D. setosum and D. savignyi were correct; it is also possible that larvae of D. paucispinum occasionally arrive at localities outside Hawaii, reach sexual maturity, and hybridize with the other two species. Counts of pure and hybrid morphotypes in other populations across the western tropical Pacific revealed a low but widespread incidence of apparent F1 hybrids and backcrosses of D.savignyi and D. setosum. However, the existence of diagnostic or semi-diagnostic loci, low interspecific gene-flow estimates based on F st statistics, and the lack of Hardy-Weinberg or linkage disequilibria among individuals of pure morphology all suggest that gene introgression between the three species is limited.

Experimental study of growth in the echinoid Paracentrotus lividus (Lamarck, 1816) ( Echinodermata)

Multimodal size frequency distribution (i.e., a few individuals growing very fast and a few individuals growing very slowly) among an originally homogeneous cohort of juveniles Paracentrotus lividus is observed in reared conditions when they are 6–24 months old. The splitting of this cohort into homogeneous size-classed subgroups results in an increased growth of the smaller animals that catch up with the bigger ones in 4 months time. This indicates that the smaller animals are not genetically less productive and suggests they were inhibited in their growth due to the presence of larger ones. Supposing such growth inhibition also occurs in the natural environment, the observed mechanism could be very efficient in stabilizing field populations of aggregative echinoid species by maintaining a protected pool of small individuals with high growth potential but inhibited by the density of larger ones.

Indo-Pacific echinoids in the tropical eastern Pacific

The existing literature reports that only one species of Indo-Pacific echinoid (Echinometra oblonga), occurs in the eastern Pacific. In this study we confirm the presence of this species at Islas Revillagigedo and also report the presence of two species ofEchinothrix (a genus hitherto unknown outside the Indo-Pacific) at Isla del Coco and at Clipperton Island. We also present evidence from isozymes and from mitochondrial DNA sequences indicating that at least one individual ofDiadema at Clipperton may belong to a maternal lineage characteristic of the west Pacific speciesD. savignyi. These data are consistent with the hypothesis that the observed populations of Indo-Pacific echinoid species are recent arrivals to the eastern Pacific, as opposed to the view that they are relicts of Tethyan pan-tropical distributions.Echinothrix diadema, in particular, may have arrived at Isla del Coco during the 1982-1983 El Nifio. In addition to Indo-Pacific species, Clipperton, Isla del Coco and the Revillagigedos contain a complement of eastern Pacific echinoids. The echinoid faunas of these islands should, therefore, be regarded as mixtures of two biogeographic provinces. Though none of the Indo-Pacific species are known to have reached the coast of the American mainland, their presence at the offshore islands of the eastern Pacific suggests that, for some echinoids, the East Pacific Barrier is not as formidable an obstacle to migration as was previously thought.

Biodiversity of Shallow-Water Red Sea Echinoids: Implications For the Fossil Record

Determination of fossil echinoid diversities is an important aspect of detailed palaeon- tological studies. The comparison of recent and fossil associations can be used to elucidate the problems of determination of fossil echinoid distributions. Actuopalaeontological studies of echinoids from the Red Sea (northern Bay of Safaga, Egypt) have shown that the study of fragments within bulk sediment samples greatly increased the possibilities for determining echinoid presence and distribution. The results show the restricted distribution as well as the differential preservation potential of the various echinoids.The distribution of echinoids is primarily controlled by grain size, food availability, exposure to current activity, and predation pressure. Regular and irregular sea-urchins show the expected disjunct distributions with the former showing a more undifferentiated distribution to various hard substrates. Irregular echinoids are tightly restricted to particular types of soft substrates reflecting their adaptation to the specific grain size of the sediments. Co-occurring irregular sea-urchins show a spatial differentiation into shallow (clypeasteroids) and deeper burrowers (spatangoids). This investigation shows that important echinoid species known to occur in the Red Sea are lacking or are very rare within the study area, although a large number of different facies types are present. Patchy distributions are present for both regular and irregular sea-urchins. The determination of biodiversity is therefore seen to be largely dependent on the scale of investigation.An important implication for fossil echinoid presence are the differential effects of taphonomic agents on the various test architectures. Some species are well represented due to their common occurrences, and their comparatively robust tests or test fragments.

Phylogenetic relationships of echinoids of the family Temnopleuridae inferred from allozyme variation.

The family Temnopleuridae of the order Echinoida from Japanese waters is represented by the four echinoid species belonging to the two different genera: Temnopleurus toreumaticus, T. hardwickii, T. reevesii, and Mespilia globulus. Their phylogenetic relationships were investigated by electrophoretic analyses of 16 different enzymes. From the allozyme variation in 30 genetic loci, the Nei's genetic distances between species were caluculated and the molecular phylogenetic tree for the four species was constructed. The phylogenetic tree indicated the following: (1) Among four species of the family, T. toreumaticus and T. reevesii are the most closely related to each other and diverged later. (2) T. hardwickii is more genetically differentiated from the other two congeners. (3) M. globulus is the most distant species of the four members. These allozyme results were discussed through the comparison with other non-molecular evidence, and the divergence process of the four echinoid species was speculated.

Distribution of some Campanian and Maastrichtian macrofaunas in southeast Spain

The distribution of Campanian-Maastrichtian species of inoceramids, ammonites, echinoids and brachiopods is given for 23 fossil sites in the Internal Prebetic and Intermediate Units of the Betic Range in Alicante province, southeast Spain. Six main units (1-6) are recognized in the stratigraphical sections used as a reference to correlate the fossil sites of the Internal Prebetic. Four different lithologies (A-D) are distinguished in the Quipar-Jorquera Formation, the only unit surveyed in the Late Cretaceous outcrops of the Intermediate Units. 57 inoceramid, 8 ammonite, 15 echinoid and 2 brachiopod taxa have been identified and are listed in a table indicating the relative positions of their appearances at each locality. Some biostratigraphical and palaeobiogeographical observations are made on the identified species of inoceramids, ammonites and echinoids.

Hydrocarbons, sterols and fatty acids in sea urchin ( Paracentrotus lividus) of the adriatic sea

Aliphatic hydrocarbons, linear alkylbenzenes (LABs), sterols and fatty acids were determined in sea urchins ( Paracentrotus lividus) of the Adriatic Sea in order to study their relationship with the trophic chain. The prevailing aliphatic hydrocarbons were squalene (40.3%) and n-C 17:1 (24.9%), both of recent biological origin. LABS, on the other hand, are considered tracers of domestic wastes in marine environment. Among sterols, cholesterol (73.5%) and other Δ5-sterols are dominant, Fatty acids 16:0 (20.0%), 20:5ω3 (12.2%) and 14:0 (7.6%) were prevalent here as they are in other echinoid species analyzed by other authors. The distribution of these different compounds seems to be influenced by factors such as physiological needs, available diet and anthropogenic contamination.

Phylogeny, rates of evolution, and patterns of codon usage among sea urchin retroviral-like elements, with implications for the recognition of horizontal transfer.

Phylogenetic relationships, rates of evolution, and codon usage were investigated in a family of retrotransposons (SURL elements) found in echinoids. The phylogeny of SURL element reverse transcriptase sequences from 10 echinoid species clearly shows the phylogenetic signature of the host taxa as well as paralogous sequences that diverged prior to speciation events. Two subfamilies (1 and 5) of SURL element reverse transcriptase sequences are recognized that diverged prior to the radiation of the Echinometridae. Comparisons of synonymous versus nonsynonymous substitutions indicate that SURL elements have been active in echinoid genomes and have evolved under purifying selection for millions of years. Rates of synonymous substitution for reverse transcriptase are similar to rates of single-copy DNA evolution and to rates of synonymous substitution for the H3 and H4 histone genes, contradicting the assumption that rates of evolution are accelerated in retrotransposons. Finally, codon usage in SURL elements is biased for codons ending in A or U relative to 42 sea urchin nuclear genes. Biased codon usage is sometimes cited as evidence for horizontal transfer, but in the case of SURL elements this bias occurs in spite of a long history of vertical transmission rather than because of horizontal transfer.