1,721,041 research outputs found
THE EGGS OF AFRONURUS LESTAGE, 1924 (EPHEMEROPTERA: HEPTAGENIIDAE): A CUE FOR PHYLOGENETIC RELATIONSHIPS.
No full textEtude en microscopie electronique du filament des formes etirees chez Chondrilla nucula Schmidt (Porifera, Demospongiae).
No full textUltrastructural observations of the reaction of Chondrilla nucula (Porifera, Demospongiae) to bacterial invasion during degenerative processes.
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The budding process in Tethya citrina Sarà & Melone (Porifera, Demospongiae) and the incidence of post-buds in sponge population maintenance
No full textThe relevance of the budding process in a population of Tethya citrina inhabiting an unpredictable environment subjected to frequent anoxic crisis (Mar Piccolo di Taranto) is described, and new data about the fate of the buds after their release are provided. At the individual level, for the first time in natural conditions, it has been demonstrated that several budding events follow each other, alternating with short periods (1-2 months) of rest. At the population level, budding proved to be a continuous process, being detected throughout the 13 months of study, with a short summer decrease both in the frequency of budding specimens and bud density. This trend was markedly different from that reported for conspecific populations inhabiting stable environments, in which budding is a seasonal process. It is hypothesized that the sudden and unpredictable variations of the ecological conditions could be responsible for the onset of repeated budding events, thus stressing the role of environmental factors in affecting the asexual reproductive pattern. T. citrina buds, here investigated, tend to detach from the adult sponge within 7/15 days of their differentiation, a feature coherent with experimental data carried out under laboratory conditions. A significant relationship between the size/age of the post-buds and the onset of the asexual reproduction has been proved: in particular, the first budding event was observed in nine-month-old sponges, measuring about 7 mm in diameter. As reported for other demosponges, in T. citrina post-buds the growth rate was positively related to the water temperature, with a significant increase during the summer. In addition, a negative effect of the budding process on the sponge growth, is hypothesized for a post-bud subjected to repeated budding events. Growth rate, however, proved highly variable. (C) 2010 Elsevier B.V. All rights reserved
Post-larval development of the commercial sponge Spongia officinalis L. (Porifera, Demospongiae)
No full textThis study investigated the development of the larvae of Spongia officinalis in experimental conditions, after settlement on plastic substrates, using electron and light microscopy. The released larvae show a dark pigmented ring distinguishes the posterior larval pole. The youngest larvae, covered with a flagellate epithelium, move onwards by rotating on their longitudinal axis. Over time a creeping-like motion prevails, probably linked to the need for settlement. After a free-swimming period of 24-48 h, larvae settle on the artificial substrate by the anterior pole. At settlement, the flagellate epithelium is substituted by flattened cells, which delimit the outermost surface. Post-larvae were reared to about three months. The early phase of post-larval differentiation shows a solid interior mainly consisting of granular cells varying in shape and size. They are included in a dense collagen matrix that contains a conspicuous amount of bacteria. Lacunae are already evident in the initial phase of metamorphosis. In several of them, cell debris and nucleate cells are visible. This feature is consistent with a progressive reduction of the cell mass (autolysis). Neither choanocyte chambers nor canals differentiate. The morphogenetic process leads to a metamorph only consisting of vacuolated cells and collagen fibrils included in a thin fibrous coat
A 3-year investigation of sexual reproduction in Geodia cydonium (Jameson 1811) (Porifera, Demospongiae) from a semi-enclosed Mediterranean bay
No full textThe reproductive cycle of Geodia cydonium in a semi-enclosed Mediterranean bay (Porto Cesareo, SW Apulia) was studied with monthly frequency over a 3-year period. The investigation was carried out by utilizing a technique consisting of tagging ten individuals with a PVC stick and cutting off, by means of a metal cork borer, small samples (cylinders about 5 cm(3) in volume) from each of them for histological analysis. Sexual reproductive elements were detected in all individuals, but in the third year some specimens showed reduced reproductive activity or complete infertility. Spermatogenesis occurred in a short period (from June to August) whereas oogenesis lasted longer (from spring to late summer). Spermatic cysts occurred when the frequency of specimens with oocytes reached its maximum values. A relationship between water temperature and the onset of gamete differentiation was observed. G. cydonium is here confirmed oviparous and gonochoric with a sex ratio in favour of the females. However, in contrast with current literature on Porifera-which suggests that only a limited number of sponges, all belonging to the same species are sexually active-the sexual reproduction of this species involves all the examined individuals. This finding can be explained by the methodological approach used in this research, which differs from the traditional way of assessing the sponge reproductive cycle by analysing randomly collected specimens within a population. The study of a series of individuals over time represents a better "model technique" for investigating sponge sexual reproduction and the effect of environmental parameters on gamete differentiation
Sessile and non sessile morphs of Geodia cydonium (Jameson) (Porifera, Demospongiae) in two semi-enclosed Mediterranean bays
No full textMorphological plasticity and ecological aspects of the demosponge Geodia cydonium (Jameson) were studied from seasonal samples collected over 1 year in two semi-enclosed Mediterranean bays of the Southern Italian coast (Marsala lagoon and Porto Cesareo basin). Sponge specimens present two morphs: sessile and nonsessile, both of which showed constant size distribution and density over the studied year. Sessile specimens were larger in size than non-sessile ones. This feature is particularly evident at Porto Cesareo, where these sponges have a more compact skeletal network than at Marsala (evident both in the cortical spicule size and sponge silica content). Sessile specimens adhere to hard rocky substrates (Porto Cesareo) or phanerogam rhizomes (Marsala); non-sessile ones occur on soft bottom areas. Several morphological and structural features of the non-sessile forms differ in the two environments, but the
difference in body shape seems to play the most relevant role in enhancing the colonization of incoherent substrates.
Indeed, at Marsala, where the large amount of silt and clay determines the occurrence of a markedly reduced anoxic layer just below the surface of the sediment, non-sessile specimens of G. cydonium are fairly spherical and thus able to roll, dragged by slow circular currents. In addition, the usual association with the red
alga Rytyphlo ̈ ea tinctoria, which almost constantly
forms a thick and continuous layer around the sponge,
allows them to avoid contact with the substrate. The
non-sessile specimens from Porto Cesareo inhabit sandy
soft bottoms and are flattened. In such an environment,affected by moderate wave turbulence, the flattened shape widens the contact surface between the body and the substrate, thereby reducing the risk of stranding. The evident signs of abrasion, provided by scanning electron
microscopy investigations, on both cortical spicules and
outermost sponge surface suggest that sponges rub on
the bottom. Sediment, epibiontic organisms, and the
phanerogam leaves protect this sciaphilous sponge from
high solar radiation, allowing the specimens to live in these shallow environments
Structural and ultrastructural aspects of growth in Oscarella lobularis (Porifera, Demospongiae)
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