No description available.

Thesis (doctoral)--Université de Paris, 1876. / "Série A. no 23"--Cover.

No description available.

Inaug.-diss. Leipzig. / "Literatur-verzeichniss": 1 p. at end.

Thesis (Ph.D) - University of Queensland, 2006. / Includes bibliography.

Hexactinellid sponges differ substantially from other sponges in having syncytial tissues and the ability to propagate signals rapidly, causing the arrest of the feeding current. To confirm existing light and electron microscopic evidence of the syncytial nature of hexactinellid tissue, live tissue models were developed from Rhabdocalyptus dawsoni and Aphrocallistes vastus. A native acellular tissue extract (ATE) was made from the sponges to which dissociated tissue adhered and spread in a species specific fashion. Video microscopy shows that dissociated tissue from R. dawsoni adheres to the ATE and aggregates by fusion of pieces to form a giant, multinucleated syncytium. Fusion, corroborated by dye exchange, is characterized by the bidirectional transport of organelles, including nuclei, and bulk cytoplasm at an average rate of 2.1 um·S⁻¹. Stress fibres line the periphery of adherent preparations, and giant actindense filopodia appear to anchor tissue to the substrate. Bundles of microtubules (MTs) bridge newly fused aggregates while extensive tracts of MT bundles are oriented in all directions in larger aggregates. Aggregates can become several centimetres in diameter and can cover a 5 cm² petri dish within 6-12 hours. Inhibition of organelle motility by colcemid and nocodazole but not by cytochalasin B suggests that transport occurs along MT bundles. A protein immunoreactive with cytoplasmic dynein was identified in whole cell lysate from A. vastus, and it is suspected the same motor protein exists in R. dawsoni and other hexactinellids. No evidence was found for kinesin, although its presence cannot be ruled out. Ultrastructural evidence suggests that a membranous network may be involved in linking bulk cytoplasm to bundles of microtubules in streams, in a manner similar to the mechanism by which bulk cytoplasm is linked to microfilaments in characean algae. Transport of bulk cytoplasm and movement of individual organelles can also be seen in regenerating fragments of the whole sponge suggesting that cytoplasmic streaming may be involved in tissue morphogenesis. The fact that latex beads that are phagocytosed are also transported in streams indicates that hexactinellid sponges employ symplastic nutrient transport, like plants, rather than apoplastic nutrient transport, like animals. Because fusion and cytoplasmic streaming are features of both Rhabdocalyptus and Aphrocallistes, representatives of lysaccine and dictyonal hexactinellids respectively, it is probable that these phenomena are characteristic of the subphylum Symplasma. Propagated arrests of the feeding current were recorded from Rhabdocalyptus in response to an increase in sediment in the sea water. Development of a new preparation in which aggregates are grafted on to parts of the adult body wall that demonstrate normal pumping physiology, allowed recording of action potentials which propagate through the sponge at 0.18 cm·s⁻¹, simultaneously with the arrest of the feeding current. This is the first recording of a propagated electrical event from a sponge. Impulse conduction in these sponges can be explained by the finding that hexactinellid tissues are syncytial. These results strongly suggest that hexactinellid sponges should be distinguished from other sponges at a high taxonomic level, and pose new questions for the evolution of intracellular transport mechanisms and excitability in the metazoa. / Graduate

Thesis (M.S.)--University of Puerto Rico, Mayagüez Campus, 2007. / Tables. Printout. Abstract in English and Spanish. Includes bibliographical references (leaves 51-61).

Thesis (Ph. D.)--University of California, San Diego, 1998. / Vita. Includes bibliographical references.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references. Also available in electronic version.

Evidence concerning the ecology of American Palaeozoic sponges, excluding hexactinellids and incertae sedis, is discussed and evaluated. In addition, detailed summaries of nearly all the papers describing American Palaeozoic sponges are included. This thesis, for the most part is a compilation of available information, and is intended as such to be a guide for further investigations (especially field studies) of sponge ecology. The environment in which the Palaeozoic sponges lived was very important in deciding whether they would, be preserved as fossils or be destroyed. Muddy waters seem to have been the best for preserving sponges, while only the more solidly built forms such as lithistids and calcisponges are usually preserved on firm bottoms in clear waters. Sponges, because of their physiological make-up, are subject to rapid decay and hence usually leave little trace of their former presence in the sediments. This is especially true of the loosely built manactinellids and tetractinellids, but less so of the more solidly constructed lithistids and calcisponges. It can be seen, therefore, that, at times the ancient seas probably contained large sponge faunas, but that little record of their presence was left behind. The ecology of the sponges, in this thesis, is dealt with by epochs, an exception being that of the Carboniferous period. In the Cambrian, sponges are present in the Waucobian and Albertan series. Besides the hexactinellids, pleosponges and incertae sedis, the monactinellids are the only sponges found. These are nearly all found in shaly sediments. A muddy water environment is suggested, but it is possible that the muds might have been the only sediments capable of preserving the monactinellids. The Ordovician contains the largest sponge fauna, in number of genera and species, of any Palaeozoic system. They are found in all stages. Tetractinellids, lithistids, and calcisponges, as well as monactinellids are present but little information was found on their ecology. A muddy water environment is suggested for the monactinellids and a clear water one for the lithistids and calcisponges. The seas, at all times, appear to have been shallow. In the Cincinnatian epoch the sponges,in the area around Ohio and Kentucky,are believed to have lived in clear, limestone depositing waters and to have been periodically killed by influxes of mud. The Silurian sponges are found only in the Niagaran series. The fauna consists chiefly of lithistids and seems to have lived in relatively deep, quiet,muddy waters.. It is suggested that the salinity of the succeeding Cayugan seas may have contributed to their extinction. After Silurian times, lithistids were never very numerous in the Palaeozoic. Although rich in the remains of hexactinellids, the Devonian system contains very few genera and species of the other sponge groups. The Ulsterian series contains only Hindia fibrosa. This sponge seems to have preferred muddy waters. The Senecan series contains numerous markings attributed to the work of boring sponges. Little is known of the ecology of Carboniferous sponges. Hence the Mississippian and Pennsylvanian systems are discussed together. The Permian system contains a rather large calcisponge and lithistid fauna in which the calcisponges dominate. The Permian sponges are usually found associated with reef deposits. In Leonardian times, calcisponges usually lived on the fore-reef and the lithistids in the near-fore-reef, open sea facies. In Guadalupian times, the calcisponges lived on both the reef and near-fore-reef facies. Lithistids were not numerous, but are found mostly on the fore-reef. The Guadalupian sponges made important contributions to reef building. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate