Peristomial tube feet and plates of regular echinoids

Summary Peristomial tube feet, ampullae and plates are described in 16 species of regular echinoids. Two basic arrangements are recognised. In cidaroids and echinothurioids there are many tube feet and ampullae per column and the radial water vessel extends on to the peristomial membrane. Tube feet terminate in a small sensory pad. Ampullae are small and flattened. In other echinoids there are only ten peristomial tube feet and the radial water vessel does not extend on to the peristomial membrane. Tube feet terminate in a broad disc and ampullae are cylindrical tubes. Plate structure and pore morphology also vary and are correlated with tube foot structure. Echinothurioids are considered to be derived from a cidaroid ancestor.     

Comparative ultrastructure of spermatozoa from two regular and two irregular New Zealand echinoids

Spermatozoa from four species of echinoids found in New Zealand had morphological characteristics typical of other echinoids, including a conical sperm head with an acrosome‐capped nucleus, a midpiece, and a single long flagellum. The spermatozoa of Fellaster zelandiae, Echinocardium cordatum, Evechinus chloroticus, and Centrostephanus rodgersii also showed statistically significant differences in species‐specific morphological characteristics. Evechinus chloroticus showed the most variable sperm morphology. The irregular urchins (F. zelandiae and E. cordatum) had short, wide sperm heads (head length:width ratios 2.93:1 & 2.97:1, respectively) with a long acrosome complex, while the regular urchins (E. chloroticus and C. rodgersii) had longer, narrower heads with a short acrosome complex (ratios 5.29:1 & 3.37:1). Spermatozoa of E. cordatum from the New Zealand population shared more characteristics with those of conspecifics from the Sea of Japan than those of conspecifics from the Baltic, reflecting the membership of the former two populations in a distinct Pacific clade. Volumetric calculations showed no evidence of phylogenetic grouping. Mitochondria of E. chloroticus spermatozoa were less than half the volume of those of C. rodgersii and E. cordatum, and those of F. zelandiae were intermediate in volume. These volume measurements will be useful in physiological studies of sperm performance and quality.     

Additional regular echinoids from the upper cretaceous in the maastricht area (belgium)

Four additional species of regular echinoids from the Maastricht type-area, brought to light by intensive collecting, are described. Three of these were never reported before from the Low Countries. Their taxonomic status is discussed.     

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. Received: 19 June 2001 / Revised version: 2 October 2001 / Published online: 14 March 2002     

Prefeeding larval development time is not correlated with egg size in regular echinoids (Strongylocentrotus species)

Summary

We compared prefeeding development times, from fertilized egg to prism larva, for Strongylocentrotus embryos from four clutches of eggs (each from a different species) differing in size. Development times did not vary consistently with egg diameter, and trends among eggs of different sizes varied with stage of development. In some cases, development times for eggs of intermediate diameter (S. franciscanus) were longer than those for larger or smaller eggs. Although mean egg diameters in clutches ranged from 84 μm (S. purpuratus) to 162 μm (S. pallidus), differences in development time to the last embryonic stage (prism) were very small. We conclude that the inverse relationship between parental investment in offspring and premetamorphic development time in echinoids depends only on the functional consequences of reduced size of feeding larval stages: effects of egg size on prefeeding development time are not evident.     

Grazing preferences of diadematid echinoids in Fiji

Grazing preferences of two species of Diadema and two species of Echinothrix, including two colour morphs of Echinothrix calamaris, were investigated by gut contents analysis, in situ feeding observations, and grazing preferences trials in aquaria. Grazing preferences were compared to the distribution and abundance of diadematid sea urchins and the percentage cover of algal and seagrass species throughout Sosoikula Reef and Nukubuco Reef, Fiji. Results showed that grazing was selective, with distinct preferences between sea urchin genera, species, and colour morphs of E. calamaris. Preferred species of algae were non-calcareous, with reportedly low concentrations of tannins, phenols and bioactive compounds. Both Diadema savignyi and D. setosum selected Codium geppiorum as their most preferred species, followed by Hydroclathrus clathratus. All Echinothrix favoured Hy. clathratus, with both colour morphs of E. calamaris next selecting Padina pavonica and E. diadema selecting green filamentous algae. The seagrass species Syringodium isoetifolium was only grazed in significant quantities by E. calamaris (b) and E. diadema. This reflected species distributions in the seagrass bed. Peak abundances of diadematid sea urchins coincided with many of their grazing preferences at their maximum percentage cover. However, only E. diadema and D. savignyi had significant correlations with preferred algal/seagrass species (E. diadema with Co. geppiorum, and D. savignyi with G. marginata) throughout the subhabitats identified on the reefs.     

The role of echinoids in shaping environments

The role of echinoids in shaping the environment of marine and terrestrial biota is considered. The participation of echinoids in bioerosion, bioturbation of sediments, and their relationships with symbionts, parasites and predators, as well as the role of echinoid skeletons in rock formation, are discussed.     

Comparative variation of morphological and molecular evolution through geologic time: 28S ribosomal RNA versus morphology in echinoids.

The comparatively good fossil record of post-Palaeozoic echinoids allows rates of morphological change to be estimated over the past 260 million years and compared with rates of molecular evolution. Parsimony analysis of morphological data, based predominantly on skeletal characteristics, and parsimony, distance and maximum likelihood analyses of molecular data, from the first 380 bases from the 5' end of the 28S rRNA molecule, for 10 species of echinoid produce congruent phylogenies. The molecular sequence chosen is demonstrably far from saturation and sister groups have divergence times ranging from about 15 to 260 Ma. Parsimony analysis allows the great majority of molecular and morphological apomorphies to be placed in one of 18 independent geological time intervals, providing a direct measure of rates of evolution for periods in the geological past. Because most molecular fixed point mutations in our sequences cannot be polarized unambiguously by outgroup comparison (making the outgroup states effectively random), distance and parsimony analyses both tend spuriously to root the echinoid tree on the longest internal branch. A topology identical to that derived from morphological data is, however, obtained using Maximum Likelihood and also parsimony analysis where outgroup rooting is restricted to more conserved regions. This is taken as the correct topology for assessing rates of evolution. Overall, both morphological and molecular changes show a moderately strong correlation with time elapsed, but a weaker correlation with one another. Statistically significant differences in evolutionary rate are found between some, but not all, pair-wise comparisons of sister lineages for both molecular and morphological data. The molecular clock rate for echinaceans is three times faster than that for cidaroids and irregular echinoids. Spearman's rank correlation test, which requires only relative magnitude of changes to be known, suggests that morphological change has a slightly better correlation with time than does molecular change, averaged over all ten species. However, when just echinaceans are considered an extremely good correlation is found between the number of molecular changes and time elapsed, whereas morphological change remains poorly correlated. Thus, molecular rates approximate to a clocklike model within restricted echinoid clades, but vary significantly between clades. Averaging results over all echinoids produces a correlation that is no better than the correlation between morphological change and time elapsed.     

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.     

On the experimental hybridization of echinoids

Ohne Zusammenfassung

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On the experimental hybridization of echinoids

     

Lunar periodicities of diadematid echinoids breeding in Fiji

Gonad indices for two species of Diadema and two species of Echinothrix, including two color morphs of Echinothrix calamaris, are described for a 12-month period on Sosoikula Reef and Nukubuco Reef, Viti Levu, Fiji. Seasonal fluctuations in salinity (36.11±0.88 ppt) and water temperature (26.35±0.91°C) occurred. Gonad index data showed monthly reproductive rhythms, closely attuned to the lunar cycle. Diadema savignyi and Echinothrix diadema spawned on the full moon, and Diadema setosum and E. calamaris (white and brown color morphs) spawned on the new moon. Breeding periodicities coincided with the spring tides, thus maximizing chances of fertilization and dispersal. Such breeding cycles indicate how closely related species can co-exist with minimum risk of hybridization. Unusual sex ratios were found for all species, with an exceptionally low incidence of males. Reasons for this deviation from the typically reported 1:1 sex ratio may relate to the exceptionally high levels of tributyltin (TBT) recorded in Suva Harbor.     

Phylogeny and evolution of developmental mode in temnopleurid echinoids

The phylogenetic relationships of 24 nominal species of temnopleurid echinoid were established using molecular and morphological data sets. The analysis combined sequence data from mitochondrial 16S rRNA and cytochrome c oxidase subunit I genes and the nuclear 18S-like small subunit rRNA gene with morphological data concerning coronal, lantern, spine, and pedicellarial traits. All four data sets contain similar phylogenetic information, although each provides support at a different taxonomic level. Two data congruence tests (Templeton's test and the incongruence length difference test) suggested no significant heterogeneity between the data sets, and all data were combined in a total evidence analysis. The resulting well-resolved phylogeny suggests that Microcyphus, Amblypneustes, and Holopneustes are not monophyletic genera, and that Temnopleurus (Temnopleurus) and Temnopleurus (Toreumatica) are not closely related and should not be regarded as subgenera. In contrast to previous morphological analyses, Mespilia is found to be more closely related to Temnotrema and Toreumatica than it is to Microcyphus. The phylogeny was used to test a series of hypotheses about the evolution of developmental patterns. All species of Amblypneustes, Holopneustes, and Microcyphus are lecithotrophic, and many of these taxa are restricted to southern Australia. Planktotrophy is the ancestral condition for the temnopleurids, and the 11 instances of lecithotrophic nonplanktotrophy in this clade can be accounted for by a single developmental transition that occurred an estimated 4.4-7.4 million years ago, apparently before the migration of Microcyphus to southern Australia. The switch to a nonplanktotrophic mode of development is unidirectional with no evidence of reversals.     

Experimental morphology of the feeding mechanism in salamanders

The subarcualis rectus I muscle (SAR) in the feeding mechanism of four tiger salamanders (Ambystoma tigrinum) was removed early in ontogeny and these individuals were allowed to complete metamorphosis. This procedure resulted in postmetamorphic tiger salamanders which differed from control individuals in the size (and thus force generating capacity) of the SAR muscle. The experimental manipulation of muscle ontogeny allowed a test of previous hypotheses of SAR function in postmetamorphic individuals. Multivariate analysis of variance for kinematic variables measured from high-speed video records of feeding revealed that experimentally modified tiger salamanders did not protract the hyobranchial apparatus or project the tongue from the mouth during feeding. Removal of the SAR muscle resulted in significantly reduced hyobranchial elevation in the buccal cavity and reduced maximum tongue projection distance.     

Experimental cold modification of cranio-facial morphology

A possible relationship between cranio-facial form and growth under cold stress was investigated through a control group (N=17)—experimental group (N=14) comparison. Two groups of young rats were exposed to 90 days of 22°C and 5°C temperatures respectively. Methods of analysis included measurement of overall bodily dimensions as well as detailed examination of the cleaned, dried skulls and femora. Statistical comparison of the cold and non-cold grown rats showed a number of highly significant mean differences; particularly a narrower nose, rounder neurocranium, and shorter femur was seen in the cold stressed animals. Human anatomical homologs were briefly noted as were their possible genetic and ontogenetic causes.     

Podial sensory receptors and the induction of metamorphosis in echinoids

Larvae of Strongylocentrotus droebachiensis (Müller), Lytechinus pictus (Verrill), and Lytechinus variegatus (Leske) which are competent to metamorphose display what appears to be substratum-testing behavior prior to metamorphosis. Larvae cease swimming, partially evert the adult rudiment, and walk about examining the substratum with their five primary podia. Larvae eithe r metamorphose or withdraw their podia and resume swimming to settle again elsewhere. Scanning and transmission electron microscopic examinations of the primary podia revealed sensory receptor cells on the rim and on a conical projection at the center of the podial sucker. Each sensory cell has a single short cilium on its apical surface a axonal process at its base which contributes to the basiepithelial nerve plexus. Mature adults of the same species also have comparable sensory structures on their tube feet suckers. It is suggested that the sensory receptors on the primary podia of setting larvae, although they are not specialized larval structures, may be involved in the perception of tactil e stimuli which have been previously demonstrated to be involved in the induction of metamorphosis.     

Divergent patterns of neural development in larval echinoids and asteroids

The development and organization of the nervous systems of echinoderm larvae are incompletely described. We describe the development and organization of the larval nervous systems of Strongylocentrotus purpuratus and Asterina pectinifera using a novel antibody, 1E11, that appears to be neuron specific. In the early pluteus, the antibody reveals all known neural structures: apical ganglion, oral ganglia, lateral ganglia, and an array of neurons and neurites in the ciliary band, the esophagus, and the intestine. The antibody also reveals several novel features, such as neurites that extend to the posterior end of the larva and additional neurons in the apical ganglion. Similarly, in asteroid larvae the antibody binds to all known neural structures and identifies novel features, including large numbers of neurons in the ciliary bands, a network of neurites under the oral epidermis, cell bodies in the esophagus, and a network of neurites in the intestine. The 1E11 antigen is expressed during gastrulation and can be used to trace the ontogenies of the nervous systems. In S. purpuratus, a small number of neuroblasts arise in the oral ectoderm in late gastrulae. The cells are adjacent to the presumptive ciliary bands, where they project neurites with growth cone-like endings that interconnect the neurons. In A. pectinifera, a large number of neuroblasts appear scattered throughout the ectoderm of gastrulae. The cells aggregate in the developing ciliary bands and then project neurites under the oral epidermis. Although there are several shared features of the larval nervous systems of echinoids and asteroids, the patterns of development reveal fundamental differences in neural ontogeny.     

The significance of the radial nerve cords in asteroids and echinoids

Summary The radial nerve cords of a number of different species of echinoids and asteroids have been examined with the electron microscope. They have been shown to consist of tracts of small naked axons with discrete regions of neuropile. Synapses within these areas of neuropile have been described and their significance discussed. A careful examination has failed to reveal any connections between the ectoneural nerve and the mesodermal nerves and muscles. Synapses across the connective tissue sheet separating these regions have been proposed to account for known functional connection. A hypothetical model of the nervous system has been proposed to account for known structure and function.The author wishes to acknowledge the help of Prof. M. S. Laverack during this study. Part of this work was carried out while the author was in receipt of a Queen Elizabeth Fellowship from the Commonwealth Government of Australia.