ResumenSe realizó un estudio histológico detallado de los testisacos y espermatogénesis de Helobdella michaelseni. El sistema reproductor masculino está constituido por siete pares de testisacos esféricos localizados entre los somitos XIII/XIV a XIX/XX. Los espermiductos alcanzan los somitos XVII/ XVIII o XIX/XX. Atrio en forma de huso. Poro masculino localizado en el segmento XII a 1 /a 2 . La espermatogénesis se produce en el interior de sacos celómicos llenos de fluido. Cada testisaco está tapizado por mesotelio. En su interior las células germinales permanecen unidas por el citóforo y desarrollan poliplastos germinales. Los espermatozoides maduros son liberados a la luz de los testisacos con posterioridad a la reabsorción del citóforo. Se describieron cinco estadios durante la espermatogénesis teniendo en cuenta la maduración de los elementos germinales y los cambios en el citóforo.Palabras clave: microanatomía, testisacos, Helobdella michaelseni, espermatogénesis. AbstractA detailed preliminary histological analysis of Helobdella michaelseni Blanchard 1900 testisacs is described. The male reproductive system is composed of seven pairs of spherical testisacs found intersegmentally from somites XIII/XIV to somites XIX/XX. Spermiducts reach the back of somites XVII/ XVIII or XIX/XX. Spindle form atria. Male pore at somite XII a1/a 2 . The spermatogenesis occurs in the lu men of fluid-filled coelomic sacs. Each testisacs is clothed by mesotelium. Inside it, the germinal cells are connected to the cytophore and develop functional units called polyplasts. The spermatozoo are released into testisacs after the cytophore reabsorption. Five stages of spermatogenesis are described taking into account the successive maturation stages of germinal cells and the changes in the cytophore.

ABSTRACT. Histology of the male reproductive system of Helobdella hyalina (Hirudinea, Glossiphoniidae) in Argentina. A detailed preliminary histological analysis of Helobdella hyalina Ringuelet, 1942 male system from Los Talas, Buenos Aires, Argentina is described. Six pairs of testisacs, located between the crop caeca, form the male reproductive system. Each testisac is clothed by the mesotelium. Inside it, the germinal cells are connected to the citophore and develop functional unit called poliplast. The spermatozoa are released into testisacs after the reabsortion of the citophore. Five stages of spermatogenesis are described taking into account the successive maturation stages of germinal cells and the changes in the citophore size. Lining cells and gland cells were found in the seminal vesicle. Five different types of gland cells are placed inside the ejaculatory ducts, as well as two kinds of cells are found in its distal portion: type 1, which produces eosinophilic granular secretion, type 2, with amorphous and slightly eosinophilic. Three distinct gland cells are located in the proximal portion of the duct: type 3, which produces a strongly eosinophilic granular secretion; type 4, with a negative eosinophilic amorphous secretion and type 5, with a basophilic granular secretion. Type 5 gland cells are described for the ducts of this species only.

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Helobdella bowermani n. sp. is described from specimens collected in fine sediment of open water benthos of Upper Klamath Lake, Klamath County, Oregon. The new species has pale yellow/buff coloration with scattered chromatophore blotches throughout the dorsal surface, lateral extensions or papillae only on the a2 annulus, dorsal medial row of papillae with small papilla on a1 and larger papillae on a2 and a3, and a small oval scute (rarely triangular). Helobdella bowermani n. sp. is morphologically similar to Helobdella atli and Helobdella simplex. Molecular comparison of CO-I sequence data from H. bowermani n. sp. revealed differences of 10.6%-10.8% with Helobdella californica, differences of 12.2%-13.7% with H. atli, and differences of 12.7%-13.2% with H. simplex.

The Island of Martin Garcia lies at the confluence of the Uruguay and Paraná Rivers (upper Río de la Plata). This island is an outcrop of the crystalline basement. Due to basalt exploitation the island exhibits several ponds covered by carpets of free-floating macrophytes. Seven major environmental variables were measured: water and air temperature, percentage of oxygen saturation, dissolved oxygen, electrical conductivity, total dissolved solids and pH. Eleven leech species were found, Helobdella striata, H. diploides, H. adiastola and H. hyalina were new records. UPGMA clustering of species based on their occurrence in different ecological conditions revealed three main species groups. Canonical Correspondence Analysis (CCA) explained 97.2% of the correlation between species and environmental variables. H. triserialis shows the widest range of tolerance, H. hyalina shows positive relationships to conductivity; H. diploides shows a high correlation with dissolved oxygen, H. striata, H. lineata, and S. similis are negatively correlated with water temperature, and H. simplex is positively correlated with pH. Relationships between the species richness (S) and the sampling sites were negatively correlated with water temperature and positively correlated with dissolved oxygen. Leech biodiversity from the water bodies of Martín García Island, shows a great diversity of species and a wide plasticity regarding the characteristics of the environmental factors considered.Keywords: biodiversity, CCA, cosmopolitan, ecology, endemics, leeches. A Biodiversidade e a Ecologia de

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ABSTRACT. Temporal (May 2005 to February 2006 and habitat distribution (pools and riffles) of Hirudinea species was analyzed at a post urban reach from Esquel stream (Chubut province, Patagonia, Argentina). Site was located 5.7 km downstream a Waste Treatment Plant. Mean values of nutrients: ammonia, nitrates and soluble reactive phosphate, as well water conductivity, turbidity and total suspended solids indicated physical and organic pollution. Leeches assemblage was composed by the glossiphonids: Helobdella scutifera Blanchard, 1900, H. michaelseni (Blanchard, 1900, H. simplex (Moore, 1911), Helobdella sp., H. hyalina Ringuelet, 1942, H. obscura Ringuelet, 1942 and the semiscolecid Patagoniobdella variabilis (Blanchard, 1900). From these H. hyalina and H. obscura are new records for Chubut province. Helobdella hyalina (810 ind.m -2 ) and H. simplex (465 ind. m -2 ) clearly dominated the assemblage at the reach. Only H. simplex displayed a spatial preference being significantly more abundant in pools than in riffle habitats (p<0.001). Species recruitment occurred mostly at September, December and March when juveniles were very abundant. Although several species of Helobdella were able to live in the disturbed section of the stream, only H. simplex and H. hyalina sustained large populations at the site and can be considered as tolerant to organic enrichment. This information is valuable to future studies on stream condition assessment in mountainous areas in Patagonia, and in other areas in which these species are present.

At species level, leeches were good indicators of water quality of streams.• Occupancy modelling offers a new methodology to understand how the species behave along a stressor gradient. • The species sensitivity description in terms of occupation, will allow researchers to generate more accurate biotic indices.