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  • 1
    ISSN: 1432-234X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Male and female echinoids are almost always separate, and seldom exhibit pronounced sexual dimorphism. In the most extreme previously known examples of sexual dimorphism, ova, zygotes, and juveniles are housed in a shallow depression in the surface of the test, or in a deepened petaloid ambulacrum. A new species of urechinid holasteroid,Urechinus mortenseni, is described in which juveniles are brooded inside a deeply invaginated extension of the body wall suspended from the interior edges of the female's apical plates. Although technically not inside the test, the juveniles are completely invisible from the exterior, and are contained in a series of brood pouches that communicate with the environment only through a small opening at the apex. This is the first complete description of brooding in the Holasteroida. The morphology of the brooding system is described, and a new terminology is erected to refer to the completely novel features of the system: the apical aperture, birth canal, and brood pouches. The plating, spines, and pedicellariae of the brooding system are also described. The salient characteristics of the brooding system found inU. mortenseni are contrasted with those of brooding strategies in other echinoderms. The new species is compared with other holasteroids. For the first time, a brooding system is also described inPlexechinus nordenskjoldi, which implies that it is closely related toU. mortenseni. This casts doubt on the integrity of the two genera, and suggests that a phylogenetic revision is required to highlight the unique features found not only in these unusual urechinids, but in other holasteroids as well.
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  • 2
    ISSN: 1432-234X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Echinoids usually broadcast gametes, and do not generally engage in a high degree of parental care. However, when they do, juveniles are typically maintained among the spines, or in shallow, external depressions in the test itself. The brooding Antarctic holasteroids Urechinus mortenseni and Plexechinus nordenskjoldi are bizarre exceptions: females develop an elaborate brooding system in which a small number of direct developing young are protected. Ontogeny of post-natal brooding urechinids is marked by profound divergence in the growth trajectories of male and female apical systems. In females, this leads to dramatic departures from the patterns found in all other echinoids. Otherwise, coronal skeleton allometry of males and females is almost identical. Juveniles in brood pouches grow larger than the diameter of the apical aperture through which they must pass to reach the external environment. The apical plates, from which the brooding system is suspended, “hinge” downward to enlarge the aperture, allowing the young to emerge from the female. A possible origin for the brooding system suggests derivation by centripetal plate addition from the ocular plates in the coronal skeleton. We develop a contrasting model for the origin of the brooding system that relies on a proposed homology between genital and periproctal elements of the apical system of echinoids and the more highly developed dorsal skeleton of other echinoderm classes.
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  • 3
    ISSN: 1432-234X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Circular marks, flush with the test or slightly depressed, exist on the test surface of various echinoid species. Fifty-six species belonging to regular and irregular echinoids were examined in order to describe the diversity and structure of these marks and to discuss their origins, with particular emphasis being put on the spatangoids Heterobrissus niasicus and Maretia planulata. Investigations combine statistical, light and electron microscopical methods. The marks correspond to surrounding ordinary tubercles in their size, their distribution on the test, their structure and their microstructure (stereom meshwork). Marks recolonized by miliaries and marks overlapping each other attest that they were made during the life of the sea urchins. This hypothesis is strengthened by comparisons between marks and artificially extracted tubercles. The microstructure of numerous marks displays original patterns with blunt broken surfaces or concentric structures suggesting that these marks result from skeletal fracture and resorption processes. From the structure and distribution of these marks it is argued that they are formed by the natural removal of tubercles. Two possible origins are retained: they are scars resulting from a traumatic extraction of spines and tubercles, or they are due to an autotomy of tubercles and associated spines, a process ontogenetically controlled and always combined with sparse or heterogeneous tuberculation. The marks resulting from these two processes are not randomly distributed either on the test or between different groups of echinoids. Their distribution and abundance are strongly involved in the ornamentation of the test.
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  • 4
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
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  • 5
    ISSN: 0886-1544
    Keywords: maytansine ; vinblastine ; diphenylpyridazone ; colchicine ; taxol ; tubulin ; microtubule ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We have investigated the effects of the microtubule poison rhazinilam on microtubule assembly in vivo and in vitro. In mammalian cells, rhazinilam mimics the effects of taxol and leads to microtubule bundles, multiple asters, and microtubule cold stability. In vitro, rhazinilam protected preassembled microtubules from cold-induced disassembly, but not from calcium ion-induced disassembly. Moreover, both at 0°C and at 37°C, rhazinilam induced the formation of anomalous tubulin assemblies (spirals). This process was prevented by maytansine and vinblastine, but not by colchicine. Preferential saturable and stoichiometric binding of radioactive rhazinilam to tubulin in spirals was observed with a dissociation constant of 5 μM. This binding was abolished in the presence of vinblastine and maytansine. In contrast, specific binding of radioactive rhazinilam to tubulin assembled in microtubules was undetectable. These results demonstrate that rhazinilam alters microtubule stability differently than taxol, and that the overall similar effects of rhazinilam and taxol on the cellular cytoskeleton are the consequence of two distinct mechanisms of action at the molecular level. © 1994 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
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  • 6
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Seasonal variation in microhabitat use and activity of 14 giant kokopu Galaxias argenteus, a drift-feeding galaxiid fish, was compared using radiotelemetry.2. During winter giant kokopu predominantly used low velocities and intermediate depths by night and day. Activity recorded during 24 and 72 h periods indicated that fish were consistently active at night and inactive during the day. Activity data corresponded with point-in-time habitat use data, both of which indicated that fish were concealed amongst cover during the day and used open water habitats at night.3. During summer, giant kokopu used higher water velocities, shallower depths and coarser substrata, particularly at night but also occasionally during the day relative to winter. Giant kokopu were active by both day and night in summer, although periods of activity were less defined and less predictable than during winter.4. Adults used predictable home reaches at base-flow, with most individuals repeatedly using of one or two cover locations within their ‘home’ reach. Reaches used by fish were relatively short (rarely exceeding 26 m) irrespective of season and always included a single pool-riffle sequence.5. Diel and seasonal behaviour of giant kokopu was generally comparable with that exhibited by other drift feeding fish species in small temperate streams. However, the nocturnal activity of giant kokopu contrasts with activity patterns in various salmonids, indicating that the impact of predation by different drift feeding fish may vary considerably.
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  • 7
    ISSN: 1432-2056
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A seventh species of Plexechinus, Plexechinus sulcatus sp. nov., is described from material collected at 585 m from an R/V “Marion Dufresne” station northwest of the Kerguelen Islands. It differs most markedly from its congeners in possessing a distinctive aboral sulcus in the anterior ambulacrum, which is unique in the Plexechinidae. There is strong phylogenetic evidence that P. sulcatus is the sister group to a clade containing P. cinctus and P. hirsutus. The implications of this placement are discussed in the light of previous work on the evolutionary biology of holasteroids.
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  • 8
    Publication Date: 2018-10-18
    Description: Journal of the American Chemical Society DOI: 10.1021/jacs.8b08595
    Print ISSN: 0002-7863
    Electronic ISSN: 1520-5126
    Topics: Chemistry and Pharmacology
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