The elucidation of the life cycle of Saccocoelioides nanii Szidat, 1954 (Digenea: Haploporidae) using molecular techniques.

In South America, the knowledge of trematode diversity parasitizing freshwater fishes is still scarce, as less than 5% of the freshwater fish fauna has been examined for parasites. A similar situation applies to studies on digenean life cycles, which have become increasingly rare. Among the digenean families parasitizing freshwater fishes in the region, Haploporidae is considered the richest in species diversity. However, information about the developmental stages of haploporid life cycles remains fragmentary. Particularly, in Argentina, nine cercariae attributed to the family Haploporidae have been described using morphological analysis, and only two life cycles of this family have been completely elucidated. In this study a new type of cercaria, morphologically assigned to the family Haploporidae and collected from the snail Heleobia parchappii (Cochliopidae) in Los Padres shallow lake, Buenos Aires province, was identified using morphological and molecular techniques. The molecular analysis, based on 28S and ITS2 sequences, revealed that the cercariae were 100% identical to adult specimens of Saccocoelioides nanii (Haploporidae) parasitizing the fish Prochilodus lineatus (Prochilodontidae) from Los Talas, Buenos Aires province. Our results not only provide information about the life cycle of S.nanii but also show that a molecular and morphological approach can be extremely useful in identifying the developmental stages of digeneans and elucidating their life cycles.

Spatio-temporal variations in larval digenean assemblages of Heleobia parchappii (Mollusca: Cochliopidae) inhabiting four human-impacted streams.

In the last years, a growing number of studies have focused on the search for biological indicators of human impact in freshwater environments. Given their susceptibility to different types of impact, larval digeneans have been considered as useful tools for the study of temporal variations in parasite communities. However, few studies have been carried out in lotic environments. For that reason, the spatio-temporal variations of the larval digenean assemblages parasitizing the gastropod Heleobia parchappii were analysed in four human-impacted streams, located on the coast of Argentina. In total, 4800 specimens of H. parchappii were collected seasonally, and 12 digenean species belonging to eight families were registered. Three of the streams showed similar species presence but, during spring and summer, the streams located within the city presented lower species presence than the streams located in the urban periphery. By contrast, the spatial prevalence values evidenced a higher variation between the environments. Streams located in the urban periphery showed higher prevalence values throughout the year, compared to those calculated for streams located within the city. The spatio-temporal variations of larval digenean assemblages parasitizing H. parchappii seem to be mainly influenced by the diversity and vagility of definitive hosts, the types of digenean life cycles and habitat characteristics. However, environmental disturbances derived from anthropogenic activities are highlighted as the probable main factors that may affect the composition and dynamic of these parasite assemblages.

The role of the invasive polychaete Ficopomatus enigmaticus (Fauvel, 1923) (Serpulidae) as facilitator of parasite transmission in Mar Chiquita coastal lagoon (Buenos Aires, Argentina).

In Mar Chiquita coastal lagoon (Argentina), the reefs of the invasive polychaete Ficopomatus enigmaticus (Serpulidae) serve as concentration areas for invertebrates and vertebrates and as potential foci of parasite transmission (mainly digeneans). To analyse the role of F. enigmaticus as facilitator of parasite transmission, and to evaluate the influence of the habitats selected by 2 species of cochliopid snails (Heleobia conexa and Heleobia australis), on the richness and on the prevalence of the digenean assemblages that parasitize them, 1945 snails were collected from 2 sampling sites. The comparisons between larval digenean communities parasitizing both snail hosts revealed significant differences related to the overall prevalence and the prevalence contributed by birds in the snails collected from reefs. These results support the idea that the reefs may increase the number of links between intermediate and definitive hosts of digeneans, facilitating parasite transmission only when the aggregates of F. enigmaticus become the unique habitat of the snail host. This first report of an exotic species acting as facilitator of parasite transmission in an estuarine area highlights the importance of analysing the effects of the assimilation process of exotic species by recently colonized environments (including the possible effects on parasite transmission).

Testing temporal stability of the larval digenean community in Heleobia conexa (Mollusca: Cochliopidae) and its possible use as an indicator of environmental fluctuations.

Larval digeneans have been proposed as indicators of abundance and diversity of vertebrate and other hosts as well as environmental disturbances. To evaluate its response to environmental changes and its potential use as an indicator of environmental fluctuations, the temporal stability of the community of larval digeneans in Heleobia conexa was comparatively analysed in 4 separate years (1996, 1999, 2004 and 2005) in Mar Chiquita coastal lagoon (Buenos Aires province, Argentina). In total, 4579 specimens of H. conexa were collected and 22 digenean species were observed. Overall prevalence presented inter-annual and seasonal differences. These differences correlate with seasonal changes in composition of the vertebrate definitive host community and with the elimination of the preferred habitat of H. conexa in 1999. In general, the larval digenean community of H. conexa showed a yearly re-establishment following the annual cycle of H. conexa and the presence of definitive hosts. This annual restructuring allowed inferences about the effects of short-term environmental changes in the lagoon. According to these observations, the larval digenean community of H. conexa could be considered as a good bio-indicator with quick response to environmental disturbances.

Seasonal stability and spatial variability of parasites in Brazilian sandperch Pinguipes brasilianus from the Northern Argentine Sea: evidence for stock discrimination.

The use of parasites as biological tags allowed the identification of two stocks of Brazilian sandperch Pinguipes brasilianus, in the Bonaerense region of the Argentine Sea. A total of 156 adult specimens of P. brasilianus were examined for parasites. Temporal variability in parasite burdens was assessed from fish caught seasonally in coastal waters of two zones, south Bonaerense (during autumn and winter) and north Bonaerense (during summer). Additional data from a previous study, comprising P. brasilianus caught during spring in these two zones, as well as in two populations from north Patagonian gulfs were used for comparative analyses of spatial variability. A total of 14 193 metazoan parasites belonging to 19 species were found. Comparisons of seasonal variability in pooled samples and within each locality showed that locality effects exceeded seasonal ones, suggesting the possible existence of two discrete stocks in the Bonaerense region. These findings were strongly supported by discriminant analyses and comparisons of prevalence and abundance between zones, after pooling seasonal samples within each zone. Further evidence of the discreteness of both stocks was assessed by inclusion of samples from Patagonian gulfs in the discriminant analysis, confirming that their differences were at a inter-population level. The parasite species that contributed most to the separation of the samples were generally those identified as biological markers in previous studies. Differing oceanographic conditions are discussed as potential causes of inter-population variation of parasite burdens.

Some ecological aspects of the copepod parasites of the common hake, Merluccius hubbsi, from the Argentine-Uruguayan coasts.

A total of 2164 common hake Merluccius hubbsi captured in the Argentine-Uruguayan Common Fishing Zone was examined for parasitic copepods. The fish were infested with Chondracanthus palpifer and Neobrachiella insidiosa f. lageniformis, the former parasitizing the buccal cavity and the latter the branchial arches. C. palpifer showed an increase in both prevalence and intensity in relation to the host size; infestation with N. insidiosa f. lageniformis decreased with increasing length of hake. Attachment site preferences and variations in the parasite distribution patterns as related to the host biology were observed. Evidence of negative association between copepod species and seasonal changes in the parasite composition was also found.

Description of a new species of Maritrema (Digenea:Microphallidae) from Mar Chiquita coastal lagoon (Buenos Aires, Argentina) with notes on its life cycle.

Adults of Maritrema bonaerensis n. sp. (Digenea:Microphallidae) were collected from the intestine of the gulls Larus maculipennis and Larus atlanticus from Mar Chiquita coastal lagoon, Buenos Aires province, Argentina. The new species differs from M. pulcherrima Travassos, 1928 in having smaller sucker ratio, longer intestinal ceca, ovary not lobed, and larger eggs, and from Maritrema prosthometra Deblock and Heard, 1969 it differs in having larger suckers, smaller vitelline follicles, and in the absence of pars prostatica. It differs from Maritrema acadiae (Swales, 1933) in having larger body and pharynx and longer cirrus. It differs from Maritrema paracadiae Ching, 1974 in the larger pharynx, longer cirrus, and in the absence of prominent prostatic cells. From Maritrema majestova Ke, 1976, it differs in having a larger body, smaller eggs, and a long and protusible cirrus. Finally, M. bonaerensis differs from Maritrema chiricae Deblock, 1975 in the larger body, longer cirrus, and in the morphology of the seminal vesicle. Sporocysts and metacercarial stages isolated from the snail Heleobia australis australis and from the crabs Cyrtograpsus angulatus and Chasmagnatus granulata, respectively, suggest that those invertebrates could act as intermediate host in the life cycle of the new species in the lagoon. This assumption is supported by evidence derived from natural and experimental infections, from studies on biology of the actual and presumed hosts, as well as from previous reports on life cycles of species of Maritrema with similar transmission patterns.

Contracaecum multipapillatum (Nematoda: Anisakidae) from Egretta alba (Aves: Ardeidae) and comments on other species of this genus in Argentina.

During a parasitological survey of aquatic birds in Mar Chiquita coastal lagoon (Buenos Aires province, Argentina), specimens of Contracaecum Raillet & Henry, 1912 sp. were found in the esophagus and stomach of the great egret Egretta alba (Gmelin, 1789) (Aves: Ardeidae). The nematodes were identified as Contracaecum multipapillatum (Drasche, 1882) on the basis of the following features: ratio of ventricular appendage length to esophagus length, ratio of intestinal caecum length to esophagus length, spicule lengths, number and arrangement of postcloacal papillae (3-4 pairs of adanal papillae, 1 double pair, and a subterminal group of 2 subventral and 3 sublateral pairs). A complete description of the adult specimens of C. multipapillatum is given in the present paper, together with a discussion regarding the validity of other species of Contracaecum reported from Argentina. Contracaecum philomultipapillatum Labriola and Suriano, 1996 is reduced to a junior synonym of C. multipapillatum, and Contracaecum longicaecum Schuurmans Sterkhoven, 1952 is considered a species inquirenda. A revision of Contracaecum spheniscus Boero and Led, 1970 based on appropriate material is necessary.

Mazocraeid monogeneans parasitic on Engraulid fishes in the southwest Atlantic.

Two species of mazocraeid monogeneans are reported for the first time from Argentinean-Uruguayan engraulid fish hosts, Engraulis anchoita and Anchoa marini. Mazocraes australis n. sp. collected from the gills of E. anchoita is described: this new species can be distinguished from the other congenerics by the number of genital hooks in the copulatory organ, the relative size of clamps, and the number of hooks in the terminal lappet. Pseudanthocotyloides heterocotyle found in the gills of E. anchoita and A. marini is redescribed. The diagnosis of both mazocraeid genera are also emended.

Clarification of the identity of copepods of the genus Chondracanthus parasitizing Merluccius hubbsi from Argentinean waters.

In an attempt to clarify the number and identity of copepod species of the genus Chondracanthus Delaroche, 1811 parasitizing common hake Merluccius hubbsi Marini, 1933 from Argentinean waters, a total of 4,569 fish were examined. All of the 995 copepods of the genus Chondracanthus collected from hake showed identical morphology and were identified as Chondracanthus australis Ho, 1991. This species was detected on fish longer than 15 cm of total length and showed an increase in both prevalence and mean intensity in relation to the increase in the size of the host. The highest prevalence and mean intensity were 53.55% and 2.51, respectively. According to our results that coincide with those of other investigators, C. australis seem to be the only species of this genus harbored by M. hubbsi from Argentinean waters.

Morphological studies of Ancyracanthopsis winegardi Wong & Anderson, 1990 (Nematoda: Acuarioidea) and larval stages of acuariid nematodes parasitic in Larus dominicanus Lichtenstein (Aves: Laridae) from Argentina.

Ancyracanthopsis winegardi Wong & Anderson, 1990 (Nematoda: Acuarioidea) is described from Larus dominicanus Lichtenstein (Aves: Laridae) on the Southwest Atlantic coast (38 degrees 42 minutes S, 59 degrees 47 minutes W). The main character used to distinguish species of Ancyracanthopsis is the morphology of the ptilina. Thus, although the specimens described here have some differences in the morphology and size of the spicules and in the female genitalia, they were referred to A. winegardi because they have a very similar ptilina. This is the first record of a member of Ancyracanthopsis from larid birds and for A. winegardi in the Southwest Atlantic coast. We have also studied acuariid larvae found inhabiting the gizzard alongside adult specimens of A. winegardi. Among those larvae, two morphological groups were clearly distinguished. The first group was characterised by the absence of ptilina and the presence of spicular primordia and rectal cells (third-stage larvae). The second group could be distinguished by the presence of ptilina and partly-developed genitalia (fourth-stage larvae). In order to identify the larvae, a Principal Component Analysis was applied to morphometric data taken from the third-stage larvae. These results and the morphology of the partly-developed ptilina of the fourth-stage larvae indicated that the larval stages found in L. dominicanus appear to belong to Sciadiocara haematopodi, Cremonte, Navone & Etchegoin, 1999.

A new species of Sciadiocara Skrjabin, 1916 (Nematoda: Acuariidae) parasitic in shorebirds in Argentina.

In the present paper we describe a new species of the genus Sciadiocara from Haematopus palliatus from the Mar Chiquita coastal lagoon (37 degrees 46' S, 57 degrees 27' W), Argentina. We provide two host records (H. palliatus and Larus dominicanus) for the genus, both from Buenos Aires province, Argentina. S. haematopodi n. sp. closely resembles S. legendrei Petter, 1967. The new species can be distinguished by the morphology of the distal end of the left spicule, the shorter length of the right spicule, the number of pre-anal papillae and the ratio of the length of the vagina vera to the length of the vagina uterina.

Resurrection of Perissopus galeorhini (Yamaguti, 1936), with notes on the genus Perissopus Steenstrup & Lütken, 1861 (Copepoda: Pandaridae) parasitic on sharks.

Recently collected copepod parasites on the narrownose smooth-hound shark Mustelus schmitti Springer revealed enough similarities with Perissopus galeorhini (Yamaguti, 1936) to be considered conspecific. Comparison of these specimens with the types of P. oblongus (Wilson, 1908) showed that P. galeorhini and P. oblongus are distinct species. Therefore, P. galeorhini is considered a valid species rather than a synonym of P. oblongus, as it has been treated since the revision of Cressey (1967). Descriptions of P. galeorhini from M. schmitti and type-material of P. oblongus are provided along with a discussion on their taxonomic status. P. galeorhini differs from P. oblongus in features relating to the anterior margin of cephalothorax, the dorsal plates of the third pedigerous segment and details of the segmentation and armature of the appendages. In addition, an amended diagnosis of Perissopus Steenstrup & and Lütken, 1861 is given, including characters not previously considered by Cressey (1967) such as: the dorsal plate of segment 2 can be small, widely separated, covered by the posterior end of the lateral processes of the cephalothorax and not always extending to the posterior border of the plates of segment 3; and the rami of legs 3 can be 2-segmented.