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  • 1
    Electronic Resource
    Electronic Resource
    Utrastructural study of oogenesis and oocytic degeneration in Pecten maximus from the Bay of St. Brieuc (1989)
    Springer
    Marine biology 103 (1989), S. 339-348 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An ultrastructural study of oocytic development enabled the identification of changes occurring during oogenesis in Pecten maximus collected from the Bay of St. Brieuc, France, in 1987. “Auxiliary cells”, closely associated with developing oocytes were observed. Each oocyte seems to be associated with only one secretory cell, which is characterised by an abundant rough endoplasmic reticulum at the onset of vitellogenesis. Contact between this cell and a developing oocyte is maintained by a desmosome-like junction which can be observed when the vitelline coat is formed. These “auxiliary cells” seem to play a trophic role in vitellogenesis, and may be involved in the formation of the vitelline coat of the oocytes. Oocytic degeneration is discussed in detail; in this species, it is a continuous phenomenon of varying intensity throughout the year. The ultrastructural changes resulting in lysis of the oocyte are described, and the evolution of atretic oocytes is examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00397268
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  • 2
    Electronic Resource
    Electronic Resource
    Mode of particle ingestion in five species of suspension-feeding bivalve molluscs (1991)
    Springer
    Marine biology 108 (1991), S. 255-261 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In order to elucidate the mode of particle ingestion and the functional anatomy of the oesophagus in bivalves, a histological study was performed onMytilus edulis (Mytilidae),Crassostrea virginica (Ostreidae),Placopecten magellanicus, Chlamys varia, and juvenilePecten maximus (Pectinidae). Specimens were sampled from various sites in New Brunswick, Canada, and Brittany, France, from 1987 to 1989. The buccal, peribuccal, and oesophageal epithelia of all species contained a dense distribution of actively secreting mucocytes, although these were somewhat less abundant inCrassostrea virginica, which also has the shortest oesophagus. Mucocyte morphology, while constant within a family (Pectinidae), showed clear differences among families. Both acid and neutral mucopolysaccharides were secreted by the epithelial mucocytes of all species. Mucus and mucus-particle masses were observed in the peribuccal and buccal regions, as well as in the oesophageal lumina of all species, even in those specimens which had been maintained without feeding (Placopecten magellanicus) or held out of water for 48 h (C. virginica) prior to dissection and fixation. These results indicate that a basal level of mucus production and transport is continuous on the peribuccal, buccal, and oesophageal ciliated epithelia, regardless of the particle concentration in the external medium. Buccooesophageal glands, generally thought to be absent in the Bivalvia, were observed in one of the species examined (M. edulis). It is concluded that the mode of particle ingestion in these suspension-feeding bivalves is via ciliatransported mucus masses; the presence of buccooesophageal glands inM. edulis suggests a digestive role for the oesophagus in this species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01344340
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  • 3
    Electronic Resource
    Electronic Resource
    Chemoautotrophic symbionts and translocation of fixed carbon from bacteria to host tissues in the littoral bivalve Loripes lucinalis (Lucinidae) (1989)
    Springer
    Marine biology 101 (1989), S. 305-312 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Specimens of Loripes lucinalis (Lucinidae) living in reducing sediments were collected near a sewage outfall at low tide on the Moulin Blanc beach, Brest, France, from January to March 1987. Electron microscope studies revealed numerous Gram-negative-type bacteria in the gill cells. Ribulosebiphosphate carboxylase, a diagnostic enzyme of the Calvin-Benson cycle of CO2-fixation was measured only in the gill extracts. Various tissues of L. lucinalis were examined for activity of APS reductase, (EC 1.8.99.2), ATP sulphurylase (EC 2.7.7.4) and rhodanese (EC 2.8.1.1), enzymes involved in sulphide oxidation. APS reductase was only found in symbiont-containing tissues, i.e., gills. These enzymatic studies characterise the symbionts as chemoautotrophic sulphide-oxidizing bacteria. Histoautoradiography demonstrated that part of the carbon dioxide fixed by symbiotic bacteria in the gills is translocated to symbiont-free tissues of the bivalve. The ultrastructure of the gill is detailed and a nomenclature based on established and new terminology is proposed to describe the various cellular types comprising the gill filament.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00428126
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  • 4
    Electronic Resource
    Electronic Resource
    Early development of the gill and implications for feeding in Pecten maximus (Bivalvia: Pectinidae) (1994)
    Springer
    Marine biology 119 (1994), S. 405-412 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Despite the importance of understanding feeding in the early stages of bivalve development, little information is available concerning the organogenesis of the bivalve gill. The present study used histological and scanning electron microscopical techniques to present a detailed account of gill development in the early stages of the scallop Pecten maximus L. (Bivalvia: Pectinidae). Live specimens from larval cultures were observed daily using light microscopy, while five scallops were sampled for electron and light microscopy every 2 to 3 d from Day 18 to 35, then weekly to Day 56, with a final sampling on Day 58. Although development was continuous, four distinct stages were identified (1-primordia, 2-homorhabdic unreflected, 3-homorhabdic reflected, 4-heterorhabdic), partially recapitulating the presumed phylogenetic evolution of this character in the Pectinidae. The absence of a ventral grcove in all stages suggests that the particle transport mechanism of pectinids evolved independently of such a structure, which is found in other bivalve families. Similarly, the absence of latero-frontal cilia in all specimens up to the largest observed (4 mm) indicates that the single row found in adults is a later development, rather than a vestige of a more abundant ciliation in ancestral forms. The anatomical data, together with in vivo observations of feeding in postlarvae, suggest that the developmental stages of the P. maximus gill correspond to critical changes in gill function. The early life of P. maximus may thus be characterized by distinct functional changes in feeding.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00347537
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  • 5
    Electronic Resource
    Electronic Resource
    The osphradium in Placopecten magellanicus and Pecten maximus (Bivalvia, Pectinidae): histology, ultrastructure, and implications for spawning synchronisation (1995)
    Springer
    Marine biology 123 (1995), S. 121-129 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The bivalve osphradium is a band of putatively sensory tissue located in the gill axis, whose function is uncertain. In the present study, extending from 1987 to 1994, anatomical, histological, and electron microscopical techniques were used to elucidate the structure and ultrastructure of the osphradium in hatchery Pecten maximus L. and Placopecten magellanicus (Gmelin) (collected from Passamaquoddy Bay, New Brunswick, Canada). The osphradium consists of two distinct regions which run longitudinally on both sides of each gill axis: the osphradial ridge, and the dorsal tuft cilia region. The osphradial ridge was largely devoid of cilia other than those of the few free nerve fibres. The dorsal tuft cilia region contained free nerve fibres and ciliary tufts, separated by undifferentiated epithelial cells. No paddle cilia were observed under isosmotic fixation conditions, although under hypotonic conditions such cilia were quite common, suggesting an artefactual nature. Most of the cells of the osphradial ridge were highly secretory, the principal products being large pigment granules (in Pecten maximus) directly secreted by the Golgi bodies, and numerous small, electron-dense vesicles. These vesicles were arranged along extensive microtubule arrays in the basal region, indicative of axonal transport. These data support and extend Haszprunar's hypothesis of the role of the osphradium in the reception of chemical spawning cues and in the synchronization of gamete emission. Together with independent data on nerve pathways, osphradial sensory modalities, and monoamine localisation, an anatomical pathway and neurophysiological mediator are postulated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00350330
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  • 6
    Electronic Resource
    Electronic Resource
    Survival of Nucella lapillus in a tributyltin-polluted area in west Brittany: a further example of a male genital defect (Dumpton syndrome) favouring survival (1996)
    Springer
    Marine biology 125 (1996), S. 543-549 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A male genital defect was reported in a Nucella lapillus (L.) population at Dumpton Gap (England). This defect was termed “Dumpton syndrome” (DS) and appears to be a genetic feature. Its main characteristic is the absence of penis (aphally) in males and in females. In 1992, such a phenomenon was discovered in populations in the vicinity of Brest (Brittany, France). DS-affected females exhibit fewer tributyltin-induced imposex characteristics than expected in normal individuals. The percentage of female sterilization is thus lower, favouring population survival. In consequence, the DS is considered to be a “pollution-resistance” feature. Comparison with the Dumpton population revealed similarities and differences in the DS characteristics. It is thus hypothesized that the DS observed at the two locations is due to two different biological mechanisms. Indeed, aphallic males with a split prostate were observed but no underdevelopment of their vas deferens and testis was noted in the present study. In this gonochoristic gastropod species, the most DS-affected males in Brest possess an ovotestis and it is thus hypothesized that feminity is remnant in N. lapillus. Incidence of abnormality is ten times higher in females than in males. This suggested that a sex-difference operates in the Brest phenomenon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00353267
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  • 7
    Electronic Resource
    Electronic Resource
    Peribuccal organs ofPlacopecten magellanicus andChlamys varia (Mollusca: Bivalvia): Structure, ultrastructure and implications for feeding (1990)
    Springer
    Marine biology 107 (1990), S. 215-223 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In order to better understand the structure of bivalve peribuccal organs and relate this to existing functional paradigms of their role in feeding, the labial palps of two scallop species,Placopecten magellanicus from the Bay of Fundy, Canada (1985 and 1986), andChlamys varia from the Bay of Brest, France (1986), were examined using histological techniques and electron microscopy. The ridged palp surface displays a uniformly dense ciliation with relatively few mucocytes; these are essentially concentrated in the region of the secondary ledge and may, through their secretory activity, determine the fate of particle masses in this area. The mucus secretions of the ridged palp surface are qualitatively different from those of the smooth palp surface. Mucocytes are much more abundant on the smooth palp surface, where it is suggested that their homogeneous secretions attenuate the potentially adverse effects of anteriorly-directed cleansing and swimming currents. Two other cell types are found in the palp epithelia: ciliated cells, which are very numerous on the ridged surface and relatively rare on the smooth surface, and non-ciliated epithelial cells, which are very numerous on the smooth surface and rare on the ridged surface, where they are confined to the palp margin. In addition to the mechanical role of the ciliated cells and mucocytes, the ultrastructural characteristics of the ciliated and non-ciliated epithelial cells indicate a dichotomy of function between the ridged and smooth surfaces. The ridged surface epithelial cells present an ultrastructural specialization in the absorption of dissolved and colloidal matter, suggesting an accessory nutritive role, whereas the smooth surface simple epithelial cells show signs of active molecular synthesis. No specialised sensory cells were observed on the ridged surface; it is therefore not yet possible to conclude whether the labial palps are capable of selection based on individual particle characteristics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01319820
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  • 8
    Electronic Resource
    Electronic Resource
    Peribuccal organs ofPlacopecten magellanicus andChlamys varia (Mollusca: Bivalvia): Structure, ultrastructure and implications for feeding (1990)
    Springer
    Marine biology 107 (1990), S. 225-233 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In order to gain a better understanding of the roles of the peribuccal organs of scallops in feeding, the structure and ultrastructure of the arborescent lips ofPlacopecten magellanicus andChlamys varia were examined using histological and electron-microscope techniques. The anatomical and histological characteristics of the lips suggest that they are closely related to the labial palps. The lips are formed of a densely-ciliated, ramified oral epithelium and a sparsely-ciliated epithelium which links the ramified ciliated ridges and entirely constitutes the aboral surface. The differential distribution of the three epithelial cell types (ciliated, non-ciliated, and mucocytes), as well as the ultrastructural characteristics of the ciliated and non-ciliated cells and the secretions of the mucocytes suggest that the arborescent lips play at least four different roles in feeding: (1) as a mechanical shield to prevent the loss of mucus-bound food material in the buccal region due to muscular-driven cleansing and swimming currents; (2) as a trap for food material which is lifted out of the oral groove due to especially strong muscular-driven currents; (3) the consolidation of mucus cords from the strands arriving from the palps and of those which have been disturbed by the cleansing currents; (4) the absorption of any dissolved and colloidal matter which may dissociate from the mucus-particle masses in the buccal region. No anatomical detectors or effectors were observed which would suggest a role in particle selection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01319821
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  • 9
    Electronic Resource
    Electronic Resource
    Association between the mollusc bivalve Loripes lucinalis and a Chlamydia-like organism, with comments on its pathogenic impact, life cycle and possible mode of transmission (1995)
    Springer
    Marine biology 123 (1995), S. 523-530 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Loripes lucinalis is a littoral bivalve which has already been confirmed to harbour endo-cellular sulfur-oxidizing bacteria within its gills. Examination of the digestive gland of L. lucinalis collected from the Moulin Blanc Beach in the Bay of Brest (Brittany, France) revealed the existence of an additional association involving a Chlamydia-like organism. Three different forms of Chlamydia-like bacteria were observed: reticulate rod-shaped cells, electron-dense cells and enlarged cells. The reticulate rod-shaped cells and the electron-dense bodies are thought to represent the germinal initial body and infectious form of the bacteria, respectively. The enlarged cells were always associated with what are believed to be spherical or icosahedral phages. Initial infestation seems to occur by phagocytosis at the apical pole of the digestive cells of the tubule and duct epithelia. Within the host cell, the bacteria undergo binary fission and budding, forming an inclusion which gradually fills up the cell. Inclusions are generally between 15 and 30 μm in size, and 〉 85% of all individuals examined possessed inclusion bodies. The level of infestation varied between individuals, some being heavily colonized, but did not seem to be related to season. Histological and ultrastructural observations suggest that, once developed, the colony has three possible fates: (1) the cells will degenerate due to phage infection; (2) colony overcrowding will occur, causing the development of electron-dense bodies that will be released into the lumen; (3) the entire membrane-bound inclusion will be released into the lumen and subsequently into the pallial cavity. Inclusions within the pallial cavity may be ingested by the host or may even be phagocytized by bacteriocyte cells of the gill. It is proposed that this association could be a form of symbiosis and that L. lucinalis may, therefore, be a rare example of an organism adapted to harbour two very different symbioses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00349231
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  • 10
    Electronic Resource
    Electronic Resource
    Genetic variability of the Lucinidae:Loripes lucinalis,Lucinella divaricata and Lucinoma borealis minor (Mollusca: Bivalvia) from Brittany, France
    Amsterdam : Elsevier
    Biochemical Systematics and Ecology 17 (1989), S. 463-468 
    Details
    ISSN: 0305-1978
    Keywords: Bivalvia ; Loripes lucinalis ; Lucinella divaricata ; Lucinidae ; Lucinoma borealis minor ; diagnostic locus ; electromorphs ; electrophoresis ; genetic variability
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0305-1978(89)90025-2
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