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  • 1990-1994  (17)
  • 1985-1989  (3)
  • 1
    Keywords: Hochschulschrift
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (140 Seiten = 4 MB) , Illustrationen, Graphen, Karte
    Edition: 2020
    Language: German
    Note: Zusammenfassung in deutscher und englischer Sprache
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  • 2
    Keywords: Hochschulschrift
    Type of Medium: Online Resource
    Edition: 2021
    Language: German , English
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  • 3
    Keywords: Hochschulschrift
    In: Teil I
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (97 Seiten = ges. 20 MB)
    Edition: Online-Ausgabe 2021
    Language: German , English
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  • 4
    Keywords: Hochschulschrift
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (140 Seiten = 9 MB) , Illustrationen, Graphen, Karten
    Edition: 2021
    Language: German
    Note: Zusammenfassung in deutscher und englischer Sprache
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  • 5
    Keywords: Hochschulschrift
    In: Teil II
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (134 Seiten = gesamt 20 MB)
    Edition: Online-Ausgabe 2021
    Language: German , English
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  • 6
    Keywords: Hochschulschrift
    Type of Medium: Online Resource
    Pages: Online-Ressource (155 Seiten, 6 MB) , Illustrationen, Graphen
    Language: German
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Zoomorphology 110 (1990), S. 9-15 
    ISSN: 1432-234X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Spermatogenesis of the marine spongeHalichondria panicea begins with the break up of choanocyte chambers, choanocytes constituting the origin of spermatogonia. The transition from choanocytes to spermatogonia is direct, without cell division. Already the spermatogonia are flagellated. The ensuing large aggregates of spermatogonia are enclosed by spermatocyst-building cells. Further development takes place within the spermatocysts, mostly arranged in fields which, however, lack any developmental gradient. Within a single spermatocyst development is mostly synchronous. Spermatogonia transform into first order spermatocytes directly. The transition from spermatid to spermatozoon is characterized by an unusual prolongation of the chromatin, often resulting in a helical form of the chromosome material and a strong enlargement of the mitochondria which align with the nucleus, leading to an irregular shape of the spermatozoon. Another exceptional feature is the virtual absence of a Golgi apparatus during all stages of spermatogenesis. TheH. panicea investigated here contained only male reproductive elements, thus appear to be gonochorists. Some features of the spermatogenesis ofH. panicea, such as dissolving choanocyte chambers, the enclosure of spermatogonia by spermatocyst-building cells and the formation of a synaptonemal complex in first order spermatocytes occur in other sponge species as well; however, the early presence of flagella in spermatogonia, the absence of the Golgi apparatus and the later irregular development of nuclei, mitochondria and the spermatozoa themselves represent features hitherto not observed in sponges.
    Type of Medium: Electronic Resource
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  • 8
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    Unknown
    Deutsche Zoologische Gesellschaft
    In:  Verhandlungen der Deutschen Zoologischen Gesellschaft, 85 (2). pp. 271-276.
    Publication Date: 2018-03-01
    Description: An introduction to the structure of the Antarctic sponge fauna is given with special reference to the position of the hexactinellida. The history of the taxon Hexactinellida is shortly summarized and the circumstances leading to the insatisfactory phylogenetic and taxonomic knowledge on the group in general are explained. Among the most important problems are discrepancies between the taxonomic criteria used by palaeontologists and neontologists respectively and the scanty availability of specimens. While predominantly confined to the deep sea in most parts of the world, hexactinellids in the Antarctic occur in shallow water as well. Most Antarctic hexactinellids have a circumpolar distribution and they dominate many benthic ecosystems in terms of abundance and biomass. At least three different mechanisms by which hexactinellids influence their environment are recognized today: 1. The large hexactinellids add a three-dimensional structure to a predominantly flat environment. 2. They serve as substrate and living space for a variety of associated fauna. 3. After their death their skeletons persist in the habitat; this can lead to profound changes in the structure of the benthic community. The biology of the species Rossel/a racovitzae, occurring in two different morphological variants with different biology is presented as an example for the need for further taxonomic work on Antarctic hexactinellids.
    Type: Article , PeerReviewed
    Format: text
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  • 9
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    Unknown
    Cambridge Univ. Press
    In:  Antarctic Science, 4 (02). pp. 137-150.
    Publication Date: 2019-09-23
    Description: About 1500 photographs from three different areas along the eastern Weddell Sea shelf and slope were analysed with respect to their sponge fauna. On the basis of material collected in concurrent bottom trawls, 34 sponge taxa were identified. Cluster and multidimensional scaling analysis showed the sponges to belong to different associations. Spatial extension of the associations is judged to be between several hundred meters and about 2 km. A deeper association (390–1125 m) on predominantly muddy substrates along a transect at Halley Bay is characterized by four opportunistic demosponge species; a second association on harder substrate in shallower depths (99–225m) off Kapp Norvegia is more diverse, with hexactinellids as one dominant component. A third cluster, comprising both Halley Bay and Kapp Norvegia stations (458–626 m), is dominated by four species which constitute a subcluster within the Kapp Norvegia sponge association. Densities vary strongly within clusters and in between geographically close stations. The species associations are related to different substrates, not to depth. Within single stations most species are patchily distributed. Both association structure and species distribution within single stations can be explained on the basis of the biology of the single sponge species.
    Type: Article , PeerReviewed
    Format: text
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  • 10
    Publication Date: 2018-03-05
    Description: During the ‘Meteor’ Expedition 13 in July and August 1990 to the northern part of the Norwegian Sea off west Spitsbergen, 7 stations with a depth of 2000 m or more were sampled with Agassiz trawl or hyperbenthos sledge, 14 more with a large box corer. Sponges were found at 6 of the trawl stations and in 2 box cores. A total of 19 species occurred, most of which were new to the area. Eight of the species were encountered more often than the other 11. Literature review and check of unpublished samples showed that by distribution, frequency of occurrence or abundance these species can be defined as the typical sponge association of the Norwegian and Greenland abyssal sea. This sponge association has a wide occurrence over the deep Norwegian-Greenland seas and parts of the Arctic basins. The analysis of substrate utilization of the 8 core species shows that all of them are able to colonize soft bottom, even some that previously had been considered to be dependent on hard substrate exclusively. Alternative substrate utilization and, in some species, the adoption of an infaunallife style are judged to be major reasons for the success of these species in the deep sea. The infaunal life style of the species Thenea abyssorum, Trichostemma sol and Tentorium semisuberites is documented and population structure data are given for the first time.
    Type: Article , PeerReviewed
    Format: text
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