A new apicomplexan species, Perkinsus atlanticus, is described from gill filaments of the clam Ruditapes decussatus (Bivalvia) from Portugal, where it causes great mortality. The zoospores differ from those of other species of Perkinsus in size and shape, dimensions, insertion of the 2 flagella, and in the identity of the host. On the other hand, the life cycle stages showed some ultrastructural differences compared with Perkinsus marinus, the only species previously studied in detail. When the clams were parasitized heavily, ultrastructurally similar life cycle stages were found in foot and mantle tissues.

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The histological location, morphological fedtures and ultrastructural characters of the sporulation of the parasite causing Marteiliasis affecting cultured mussels in Galicia fit the characteristics defined for the type species Marteilia relringens The early stages of the infection are confined to the host stomach epithelium. The spreading of the parasites through the host digestive diverticula involves a n exponential increase in the number of parasites as the infection progresses, suggesting the occurrence of merogony, in addition to the well known sporulation. The infection usually triggers a host hemocytic reaction that may slow down or even stop the infection at times. The study of 5 zones of culture disclosed great spatial variability in the prevalence of Marteiliasis on mussels throughout the bays of Galicia, including a n area in which no infection was detected. The culture zones located within the bays showed higher prevalences than those located outside. There was no significant difference in the intensity of the infections among the affected zones Sporulation occurred throughout the year Several peaks of both prevalence and occurrence of heavy ~nfections took place every year. Considering the areas affected by Marteiliasis, the higher the prevalence of the infect~on the higher the mortality. In some of the studied zones, mortality was significant for the mussel farming industry.

ABSTRACT. Two types of circulating hemocytes were identified in Mytilus galloprovincialis hemolymph: hyalinocytes and granulocytes. The hyalinocytes are agranular cells and show a central nucleus surrounded by relatively small cytoplasm. The granulocytes are larger than hyalinocytes and have smaller nuclei. Three classes of granulocytes (acidophilic granulocytes, basophilic granulocytes and granulocytes containing both types of granules) were distinguished based on staining properties of their cytoplasmic granules. At the ultrastructural level, the hyahnocytes show characteristics of undifferentiated cells. The granulocytes are more differentiated and have membrane-limited cytoplasmic granules. Some granulocytes contain only small granules; others have numerous large granules and some of them contain a mix of granule sizes. Density grad~ent centnfugation allowed the separation of acidophilic granulocytes from the other types. Immunocharacterization demonstrated that the granulocytes are an antigenically heterogeneous population.

A powerful rhetoric regarding the importance of adolescents’ civic engagement and political participation is common in contemporary societies, whilst citizens, both adolescent and adults, seem to express a growing scepticism and alienation regarding politics. Even if this disengagement is debatable, as there are simultaneous signs of an increasing involvement in a variety of emerging and broadly‐defined civic and political activities, we argue that the benefits of these experiences should be scrutinized using psychological evidence‐based criteria. We rest on classical contributions from developmental psychology, educational theory and political science to define criteria that could inform the quality of participation experiences, and then present two studies that explore its adequacy. Study 1 is a cross‐sectional study that observes that higher quality civic and political experiences are connected with more complex modes of thinking about politics. In Study 2, a two‐wave longitudinal design, the quality of participation experiences is a significant predictor of change patterns of political attitudes; moreover, results support the argument that participation is not good in itself and that some experiences, with lesser developmental quality, might have a detrimental effect on adolescents’ political development.

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Continuous in vitro cultures of the clam Tapes decussatus parasite Perkinsus atlanticuswere established from infected gill fragments, infected haemolymph and parasite hypnospores isolated from infected gill fragments following incubation in Ray's fluid thioglycollate medium (RFTM). No continuous cultures could be initiated from P. atlanticus zoospores. Cultures initiated from hypnospores yielded the highest percentage of continuous cultures (100%, 6/6), followed by cultures initiated from gill fragments (93%, 43/46) and from haemolymph (30%, 3/10). Failures to establish continuous cultures were due to microbial contamination. The source of parasite influenced the success rate, the time taken to establish cultures and the size of cultured cells. In vitro proliferation of parasite cells was mainly by vegetative multiplication. Zoosporulation, yielding motile biflagellated zoospores, was observed at a low frequency (<1% of dividing cells) in every culture. Morphology of cultured cells examined with light and transmission electron microscopy corresponded to that of P. atlanticus found in clam tissues. Cultured cells enlarged in RFTM and stained blue-black with Lugol's solution, which are characteristics of the Perkinsus species cells. DNA sequences of the internal transcribed spacer (ITS) region of the ribosomal RNA gene complex matched those of P. atlanticus. All cultures were established in a medium designated JL-ODRP-2A that was similar in composition to the culture medium JL-ODRP-1 originally used to propagate Perkinsus marinus in vitro. Proliferation of P. atlanticus in vitro could be supported by the commercial culture medium (1:2 v/v) DME:Ham's F-12 with fetuin. KEY WORDS: Perkinsus atlanticus · Tapes decussatus · In vitro culture · Clam parasite · Ribosomal RNA gene complex · ITS · UltrastructureResale or republication not permitted without written consent of the publisher Dis Aquat Org 52: [217][218][219][220][221][222][223][224][225][226][227][228][229][230][231] 2002 spacer (ITS) region of the rRNA gene complex (Goggin 1994, de la Herrán et al. 2000, Robledo et al. 2000, Casas et al. 2002. Recently, Ordás & Figueras (1998) reported the in vitro culture of P. atlanticus from the haemolymph of an infected carpet shell clam. Identification of the cultured cells was based solely on their morphology (light and electron microscopy). Sequence analysis of the SSU small subunit rRNA gene, however, showed that those cultured cells did not correspond to a Perkinsus organism (Figueras et al. 2000). Continuous cultures of P. atlanticus, therefore, still need to be established.The development of continuous cultures of Perkinsus species can lead to a better understanding of this group of parasites . Cultures of the eastern oyster pathogen Perkinsus marinus, for example, have been used in a wide range of studies to address the parasite's environmental tolerance (Burreson et al. 1994, Dungan & Hamilton 1995, virulence , Bushek & Allen 1996a, Volety & Chu 1997, genetic composition (Reece et al. 1997, Reece et...