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Abstract

104 specimens of notothenioid fishes of five species (Patagonotothen longipes, P. tessellata, Champsocephalus esox, Cottoperca trigloides and Patagonotothen brevicauda) caught at two sites in the Beagle Channel (Magellanic sub-region, sub-Antarctica) were examined for the presence of thorny-headed worms (Acanthocephala). Representatives of three fish species, Patagonotothen longipes, P. tessellata, and Champsocephalus esox, were infected. Fishes caught at the eastern mouth of the channel were infected with 180 echinorhynchids representing three species, Aspersentis johni (the most numerous species), Heterosentis heteracanthus, and Hypoechinorhynchus magellanicus, and only 12 cystacanths of four polymorphids, Andracantha baylisi, Corynosoma sp., Corynosoma beaglense, and Corynosoma evae. Patagonotothen longipes was the most highly infected in the eastern mouth of the channel (prevalence 85%, maximum intensity 26). Aspersentis johni was the dominant parasite species in this host (prevalence 85%, mean abundance 4.00, maximum intensity 18) and H. heteracanthus was the sub-dominant one (prevalence 50%, mean abundance 2.60, maximum intensity 25). The infections of C. esox were the most diverse (six parasite species - three echinorhynchids and three polymorphids). Fish caught near the city of Ushuaia were infected only with six cystacanths of C. evae (intensity one). Taking into account the whole sample, C. evae was the most abundant polymorphid, represented by 10 of 18 specimens found. Three species, H. heteracanthus, A. baylisi and C. evae, have been previously reported from the low western Antarctic (H. heteracanthus also from the Kerguelen sub-region of sub-Antarctic), remaining four species seem to be endemics of the Magellanic sub-region of sub-Antarctic.
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Abstract

Effects of confinement on mechanical, structural and thermodynamic properties of uniform fluids are very well understood. In contrast, a general theory based on statistical thermodynamics for confined nonuniform and non-isotropic phases, such as the lamellar phase, is in its infancy. In this review we focus on the lamellar phase confined in a slit or in a pipe in order to illustrate various effects of confinement. We limit ourselves to the results obtained by M. Tasinkevych, V. Babin and the author for lamellar phases in oil-water-surfactant mixtures within a generic semi-microscopic model, using a mean-field approximation. We show that compared to isotropic fluids the excess grand potential contains additional terms associated with structural deformations. These terms depend on the type of the confining walls, the shape of the container and on the thickness of the lamella. As a result of the dependence of the structure of the confined lamellar phase on the shape of the container, capillary lamellarization and capillary delamellarization is found in slits and in pipes respectively.
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