Ultrastructure study of the intramolluscan stages of Meiogymnophallus minutus (digenea: gymnophallidae) in Scrobicularia plana (bivalvia) from Portugal

The fine structure of the germinal mass, brood cavity and birth canal of the rediae of the monoxenous hemiuroid digenean Bunocotyle progenetica Chabaud & Buttner, 1959

Bunocotyle progenetica is a hemiuroid digenean whose sexual adults become fully developed and lay their eggs inside the rediae in the molluscan host. In this study, the fine structure of the germinal mass, brood cavity and birth canal in the B. progenetica rediae was examined using transmission electron and confocal microscopy. The large germinal mass attached to the body wall has a cellular composition typical for this organ. The characteristic traits of this germinal mass are weakly developed supporting tissue and the presence of deep lacunae opening into the brood cavity. These lacunae presumably participate in feeding the deeply lying embryos and facilitate their release into the brood cavity. The germinal mass is also characterized by intensive degeneration of cellular elements, which may represent a mechanism controlling the offspring number, limited in this species by the size of the redial brood cavity. The brood-cavity lining consists of flattened cells bearing lamellar projections and is connected anteriorly with the epithelium of the birth canal. The brood-cavity musculature, which is well developed in other hemiuroid digeneans, is significantly reduced in B. progenetica, most likely because their cystophorous cercariae remain inside the rediae, removing the need for muscle contractions pushing them through the brood cavity. The birth canal comprises three regions distinguished by the structure of the lining and muscle arrangement. The comparison of rediae of B. progenetica with parthenitae of other digeneans has shown that the organization of the redial reproductive apparatus in this species may have been influenced by life-cycle modification.

Morpho-functional specialization of the branching sporocyst of Prosorhynchoides borealis Bartoli, Gibson & Bray, 2006 (Digenea, Bucephalidae)

Sporocysts of Prosorhynchoides borealis were obtained from the marine bivalves Abra prismatica and studied using transmission electron microscopy. The sporocyst body consists of a mass of branching and intertwining hollow tubules that ramify through the host's digestive gland and gonads. This study investigated the ultrastructure of the sporocyst branches which comprise alternate distended areas (brood chambers) with a relatively thin body wall, narrower portions with a thicker body wall (constricted areas) and terminal regions. Pronounced differences between these areas were revealed in the structure of their tegument and body cavity lining, as well as in the cellular composition of the subtegumental layers. Body wall composition in distended areas was consistent with the specialization for cercarial nurture in the brood chambers. The structure of the constrictions suggested a dual role of nutrient absorption and physical separation of adjacent brood chambers. Two types of terminal region were identified, one specialized for the investigation and penetration of host tissues and the other, in which the germinal cells are formed, for cercarial production. The overall structure of the sporocyst branches helps explain why this linear modular system, i.e. brood chambers and constrictions continuously growing into the host tissue, enables the sporocyst's long-term existence and can continuously produce cercariae in numbers comparable with those produced by rediae and/or daughter sporocyst infrapopulations in other digeneans. The origin of the nuclei in the outer tegumental layer of some branching bucephalid sporocysts is also discussed.

FIRST RECORD AND DESCRIPTION OF METACERCARIAE OF CURTUTERIA ARGUINAE N. SP. (DIGENEA: ECHINOSTOMATIDAE), PARASITE OF COCKLES CERASTODERMA EDULE (MOLLUSCA: BIVALVIA) IN ARCACHON BAY, FRANCE

A new Himasthlinae species, Curtuteria arguinae, is described as metacercariae from the cockle Cerastoderma edule (L.), collected at Banc d'Arguin (southwestern France). These metacercariae encysted preferentially in the mantle and also in the foot of cockles. Encysted and chemically excysted metacercariae were studied by light microscopy and scanning electron microscopy, respectively. Excysted metacercariae were elongated and curved ventrally. They bore a 33-spine circumoral collar. Sensory papillae were arranged around the oral sucker and also symmetrically along the ventral surface body, from the collar to the acetabulum. The dorsal and ventral tegument surfaces were densely packed with similar pointed spines. The posterior end of the body was without any spines. Among the Curtuteria species described previously, only Curtuteria haematopodis Smogorjewskaja and Iskova, 1966 had the same number of circumoral collar spines. A 6-yr field survey showed that the cockle population at Banc d'Arguin was subjected to a summer infection of C. arguinae. Curtuteria arguinae phenology of infection is characterized by interannual variability and seasonality (beginning in July-August and maximum in autumn). The first intermediate and final hosts remain unknown.

DIGENEAN LARVAE PARASITIZING CERASTODERMA EDULE (BIVALVIA) AND NASSARIUS RETICULATUS (GASTROPODA) FROM RIA DE AVEIRO, PORTUGAL

This work reviews the significant community of digenean trematodes observed infecting the edible cockle, Cerastoderma edule, and the snail Nassarius reticulatus in the channel of S. Jacinto, Ria de Aveiro Estuary, Portugal. The Digenea observed comprise 15 species, belonging to the families Bucephallidae (1), Echinostomatidae (4), Gymnophallidae (3), Lepocreadiidae (1), Microphallidae (1), Monorchiidae (1), Renicolidae (1), Strigeidae, (1), and Zoogonidae (2). The species were studied by light microscopy and scanning electron microscopy. Information is included for hosts, sites of infection, prevalence, and a brief description of parasite surface morphology. The significance of these observations is compared with the presence of these digeneans from other regions, mainly the Atlantic Ocean and Mediterranean Sea. The Ria de Aveiro is a geographical location conducive to extensive species co-occurrence resulting from the overlap between southern (Mediterranean) and northern definitive hosts of the parasites. Differences in life cycle strategies were observed and discussed.

Relation between Physical Properties of the Zona Pellucida and Viability of Bovine Embryos after Slow-freezing and Vitrification

In vitro-produced bovine morulae/blastocyst embryos (n = 119) were slow-frozen and vitrified and the physical alterations of the zona pellucida (ZP) was observed by scanning electron microscopy (SEM) to find an explanation for the loss of developmental capacity of the embryos after freezing/thawing. A control group was provided, in which embryos (n = 38) were neither frozen nor vitrified. Embryos were in vitro-cultured in a standard CO2 Heraeus incubator and their viability was assessed 24 and 48 h after the start of culture, evaluating their morphological aspect. After 24 h of culture, embryo survival rate for slow-freezing/thawed (n = 23), vitrified/thawed (n = 20) and control embryos (n = 20) was 39, 27 and 90%, and 35, 14 and 65% after 48 h of culture, respectively. For evaluation of physical changes occurring in ZP, 20 embryos were slow-frozen, 18 were vitrified and 18 were used as control. All embryos were fixed, dried and examined under an SEM. Embryo's diameter, as well as the number of pores and their diameter was measured in squares of 6.4 microm width. We observed that, on average, the diameter of the embryos (92.26 +/- 10.15 microm) did not differ significantly among all embryos. As far as the diameter of the pores in the outer surface of the ZP is concerned, the results revealed a significant difference (P < 0.05) between control (0.48 +/- 0.0025 microm), slow-frozen (0.34 +/- 0.0007 microm) and vitrified (0.27 +/- 0.0006 microm) embryos. For the number of pores, statistical differences (p < 0.05) were observed between control and vitrified embryos (45.4 +/- 7.3 vs 38.2 +/- 8.2). It is possible that ZP functions as a barrier which is positive when dealing with pathogens, but is harmful when nutrients were supplied from the outside, especially at 48 h of culture. Results indicate that the steps of cryopreservation cause alterations in ZP, with irreversible damage on the further developmental competence of bovine embryos.

Cercaria sevillana n sp, a new cercaria (Digenea: Microphallidae) from Nassarius reticulatus (L) (Mollusca: Prosobranchia) in Portugal

Cercaria sevillana n. sp. (Digenea: Microphallidae) was discovered infecting the gonads and digestive gland of the prosobranch Nassarius reticulatus (L.) (Nassariidae) collected from the Ria de Aveiro, Portugal. Cercariae were obtained by natural emission and were studied under a differential interference contrast microscope and scanning electron microscope (SEM). C. sevillana n. sp. is identical to the cercaria found by Dolgikh (1965) in the same mollusc host from the Black Sea, but erroneously named C. misenensis Palombi, 1940, which is a parasite of Cerithium rupestre Risso, 1826 (Cerithiidae). Cercaria sevillana n. sp. can be distinguished from C. misenensis by its tail being shorter than the cercarial body, as well as by differences in the pattern of penetration glands the size and shape of the stylet and excretory vesicle, and its behavioural pattern. An unusual structure of the tail of this new cercaria was observed by SEM; it is characterised by the presence of annular folded membranes arranged as overlapping flounces around its central axis. This resembles the traditional skirts of the women of Seville. Such a morphological feature of the tail has not been previously observed, but may be a feature of many microphallid cercariae.