The rotifer fauna of twenty five localities (mainly shallow lakes) from Corrientes, Argentina was studied. 136 taxa were identified, 20 ofwhich, from the genera Lecane, Lepadella, Ploesoma, Ptygura, Squatinella, Testudinella and Trichocerca are new to the Argentine fauna. Most of these are (sub)tropical in distribution, and 8 % are endemic to South America. Ploesoma africana Wulfert, Ptygura kostei n.sp., Testudinella brevicaudata Yamamoto and Trichocerca vernalis Hauer are recorded from the Neotropical region for the first time. The rotiferan species richness of this area, is remarkable. The highest diversity was recorded from vegetated lakes, with acid waters, where one locality yielded 56 species.

Eleven new species in the mayfly family Leptophlebiidae are described from larvae from Mexico and Central America. Choroterpes ungulus, n. sp., Thraulodes eccentricus [=Allen and Brusca's Thraulodes sp. B], n. sp., and Thraulodes tenulineus [=Allen and Brusca's Thraulodes sp. D], n. sp., are described from Mexico; Farrodes otiesa, n. sp., Hagenulopsis ingens, n. sp., Hagenulopsis ramosa, n. sp., Terpides diadema, n. sp., Traverella holzenthali, n. sp., and Traverella longifrons [=Allen's Traverella sp. B], n. sp., are described from Costa Rica; Traverella promifrons [=Allen's Traverella sp, C], n. sp., is described from Belize and Costa Rica; and Thraulodes grandis, n. sp., is described from Guatemala.

Deux espèces très rarement signalées, Cymbella alpina et C. stauroneiformis, ont été étudiées au microscope optique et au microscope à balayage. La caractérisation des sous-genres Encyonema, Cymbella et Cymbopleura est revue à l'aide de trois exemples : Cymbella minuta, C. cistula et C. helvetica. La position systématique de C. alpina et de C. stauroneiformis par rapport aux autres taxons étudiés et par rapport aux différents sous-genres ou la récente réapparition d'anciens genres est discutée.

A number of European species of the genus Arrenurus (Acari, Hydrachnellae) are revised. The following synonyms are established: A. hofsteni Walter and A. sinuator commutatus Viets as junior synonyms of A. latus Barrois & Moniez; A. ornatulus Viets of A. compactus Piersig; A. walteri Koenike of A. neumani Piersig; A. cyanipes (Lucas) sensu Walter and A. bucharicus Sokolow of A. papillator (Müller); A. stjoerdalensis naias Lundblad of A. coronator Thor; A. eugeminus Piersig and A. imitator Koenike of A. geminus George; A. insperatus George of A. stjoerdalensis Thor; Arrenurus brachyurus Viets of A. bifidicodulus Piersig and Arrenurus truncatellus georgei Piersig of A. truncatellus (Müller). A. spatiosus Viets has been raised to species rank, while A. papillator bicolor Viets should stand as a subspecies. A. distans Walter, A. scourfieldi Soar and A. tubulator (Müller) are considered good species. A. bueranus Münchberg, A. curtus George, A. incertus Biesiadka, A. soari George and A. paluster Thor are considered species incertae. A lectotype has been designated for A. scourfieldi. Finally, a small number of old identifications have been re-examined.

Le Sud-Ouest de la France recouvre tout ou partie de 24 départements et totalise 128.000 km2. Une première liste de 60 espèces d'Ephéméroptères ne posant actuellement pas de problème de nomenclature ni de caractérisation est dressée. En fait, le Sud-Ouest de la France est la Terra typica de 10 de celles-ci : une décrite par Joly, deux par Eaton et sept par Thomas et al. Cinq sont des endémiques pyrénéennes, du seul versant Nord semble-t-il : Baetis catharus, B. nicolae, Rhithrogena kimminsi, R. strenua et Habroleptoides berthelemyi. En raison de leur appartenance à l'hyporhithron et à l'épipotamon, Rhithrogena germanica, Ecdyonurus macani et Ephemera vulgata, devenues très rares, sont gravement menacées par les pollutions d'origine agricole et la régulation des débits, en particulier les prélèvements d'eau pour l'irrigation, autorisés ou non, lors des étiages extrêmes. Pour les mêmes raisons, Isonychia ignota, Neoephemera maxima, Brachycercus harisella et Ephemera glaucops, non retrouvées depuis plus d'un siècle, ainsi que Prosopistoma foliaceum depuis plus de soixante ans, ont probablement disparu de cette région à l'heure actuelle.

Aspects of the egg biology of the perlid stonefly, Dinocras cephalotes (Curtis), were studied experimentally. Development under constant laboratory conditions did not differ from development under variable field conditions. Exposure to 4°C, the lower threshold temperature for egg development, caused abrupt interruptions of embryonic development. Development was resumed after return to favourable temperatures, with an approximate two-week-delay. Up to six interruptions of egg development did not negatively affect hatching success, regardless of developmental stage at which disturbances occurred. However, the older embryos grew, the more rapidly development was resumed after a cold disturbance; embryos from fully developed eggs hatched even at 4°C, although this is too cold to support larval growth. While eggs at 4°C remain dormant and vital for long periods of time, eggs exposed to suboptimal temperatures (10°C) remain only temporarily dormant and eventually develop and hatch. D. cephalotes is assumed to satisfy its high thermal demand for egg development under harsh conditions, for example in arctic Scandinavia, by opportunistically using summer warmth and spreading embryogenesis over more than one year. I suggest that high cue temperatures required to initiate egg development in Scandinavian populations are adaptive and ensure that larvae in the Arctic hatch under favourable seasonal conditions.

The life cycle of Baetis liebenauae has been investigated in a lowland spring of Northern Italy that shows a relative stability of water temperature. Nine postlarvula morphological stages of the larva were identified and a «jump development» of the wingpads between stage pairs has been noted. B. liebenauae is here a typical polyvoltine species and three generations can be defined, with the late-summer/autumn generation being the main one. During this generation the species is often the dominant taxon of the benthic community and shows a high larval density. Marquet differences have been in comparison noted with the development of this species in Poland. This is probably due to the different thermal features of the two regions. A temporal shift of the main generations seems to allow the coexistence of B. liebenauae and other high density Baetidae species. In Southern Europe the species is typical of small lowland streams with slow flowing waters. Its larvae live on aquatic macrophytes and their presence on mineral substrata can be considered as occasional.

In Buenos Aires province, the river Samborombón, which is typical of the plain, was sampled monthly during 1986-1987 in research carried out both on its physico-chemical characteristics and the communities present - plankton, phytobenthos, zoobenthos -. In this paper the structure and function of phytoplankton and benthic algal communities in the different sections of the river are compared. Both communities have definite limits as their components are not shared and show different strategies. Likewise, the environmental conditions along the river are variable, leading to differences in the planktonic and benthic algae at the locations studied.

Two successive generations of Epeorus sylvicola were studied in the Tifferguine, a torrential river in Morocco (2600 m altitude, water temperature 0-22° C, snow-cover : 1-2 months/year). The life cycle took one year and larval growth depended on temperature. Larvae fed on periphyton and lived mainly on stony substrates. In spring, macrophytes overgrew the bottom river and markedly reduced the amount of non-vegetated area ; combined with maximum and potentially lethal temperatures E. sylvicola larvae disappeared in May. Consequently, annual production depended on the development stage reached by the cohort when such unfavourable conditions occurred.

The genus Paracloeodes (Insecta : Ephemeroptera : Baetidae) is newly reported from South America. Because of the discovery of species with hindwings and other characteristics not previously associated with Paracloeodes, a redescription of the genus is provided. Cladistic data suggest a South American center of origin for this Panamerican genus. Paracloeodes binodulus, n. sp., is described from larvae from northern Brazil, and is distinguished by the lack of hindwingpads and presence of small mesonotal tubercles. Paracloeodes eurybranchus n. sp., is described from larvae and female adults from north-central Argentina and southeastern Brazil; it is distinguished as larvae by the relatively large size, hindwingpads, and medially broad gills. Paracloeodes ibicui, n. sp., is described from a mature larva collected from Paraguay, and is distinguished by hindwingpads and abdominal coloration. Paracloeodes leptobranchus, n. sp., is described from larvae from Paraguay and southeastern Brazil, and is distinguished by relatively large size, hindwingpads, and slender gills.

The nymph, subimago and egg of Choroterpes (Ch.) prati n.sp. from the Matarranya river (Ebro basin, Spain) are described. The relationships between this new species and the North-African and European members of the genus Choroterpes s.s. Eaton 1881 are illustrated.

Des investigations malacologiques ont été réalisées en 1974 et en 1994-1995 dans trois prairies de la Haute-Vienne afin de préciser les caractéristiques des gîtes à limnées lorsque les parcelles sont abandonnées ou modifiées par l'application de mesures agronomiques. L'abandon d'une prairie et l'invasion de ragondins se sont traduits par des modifications dans la distribution des limnées. Lymnaea cf. fuscus a déserté le fossé principal de drainage pour coloniser les rigoles et les couloirs créés par ces rongeurs, ce qui s'est traduit par un accroissement important de la superficie du nouveau gîte. Les effectifs moyens de L. cf. fuscus et de L. truncatula ont augmenté aux dépens de ceux de L. glabra. Un autre mollusque aquatique, Physa acuta, a envahi le fossé laissé libre. Le curage des rigoles dans les deux autres prairies et leur invasion par une ou deux espèces aquatiques (L. ovata, Potamopyrgus antipodarum ou Physa acuta) se sont traduits par une extension dans la superficie du gîte aussi bien pour les mollusques colonisateurs que pour L. glabra et L. truncatula. Les effectifs des trois premières espèces sont assez importants dans ces deux rigoles ; par contre, on note une réduction du nombre des deux limnées.

This study employs histological procedure to elucidate the natural cycles of gonadal development in a population of E. radiata in the Cross River, Nigeria. The cycles of condition indices and shell-free dry mass follow a general pattern in which they increased with the sexual maturity of the species till a peak is reached in June when spawning begins. Then there is a gradual decline, as the spawning event progresses, till a minimum is obtained in October when the animal is spent. Thus, the species spawns once in a year during the peak of the rainy season (June to October). The timing of spawning is such that the young larvae stand to profit from the high plankton biomass during the ensuing dry season months.

The genus Beardius Reiss et Sublette is emended based on the inclusion of three new species, B. aciculatus, B. lingulatus and B. triangulatus netted along small rivers in the Guanacaste province in NW Costa Rica. B. aciculatus and B. parcus Reiss et Sublette also is present in samples from Vera Cruz, Mexico. A new record of B. parcus from Mato Grosso, Brazil, is given. The female of the genus is described for the first time based on B. parcus Reiss et Sublette. The genus is shown to be closely related to Paratendipes Kieffer. A cladogram is erected showing three species pair with B. aciculatus and B. parcus as the sister group of the remaining. A key to male imagines is given.

During the summers 1992 and 1993, 15 species of Clinocerinae (Empididae) were collected on Corsica. The illustrated descriptions of six new species are given: Roederiodes wagneri sp. n., Clinocera (Kowarzia) cataractae sp. n., Wiedemannia (Chamaedipsia) ariolae sp. n., Wiedemannia (Chamaedipsia) bravonae sp. n., Wiedemannia (Philolutra) kallistes sp. n. and Wiedemannia (Wiedemannia) martini sp. n.. Their systematic relations with other species are discussed. Informations is given about their geographic distribution and their habitats.

Crassabwa Lugo-Ortiz & McCafferty (Ephemeroptera : Baetidae), n. gen., is erected for a small monophyletic group of distinctive Afrotropical species previously assigned to Afroptilum Gillies and Centroptilum Eaton, including C. badia (Kopelke), n. comb., C. flava (Crass), n. comb. (type species), C. loweae (Kimmins), n. comb., and C. vitrea (Navás), n. comb. Larvae of Crassabwa are distinguished by possessing a thumb-like distomedial process on labial palp segment 2, a proximal arc of setae on the tibiae, two enlarged subapical denticles in the tarsal claws, and seven gill pairs with posteriorly oriented tracheae and anterodistal marginal serration. Adults are distinguished by possessing hindwings with two longitudinal veins and an elongate, acute costal process, and a robust segment 3 of the male genital forceps. The larval stage of C. flava is redescribed, and new figures are provided to illustrate previously overlooked characters.

Two sediment cores from acid lake Store Hovvatn were analysed for chironomid head capsule remains over a sequence spanning from about 1730 A.D. to the late 1970s. Up to 30 taxa were identified from one (0.5 cm) level in the cores. Principal component analysis of taxon relative abundances showed a gradient corresponding more or less to the sediment sample chronology. Redundancy analysis with some chemostratigraphical variables, and with pH values inferred from diatoms, indicated that chironomid community change could be explained as a response to acidification. However, most of the taxa that declined or disappeared up-core are known to occur in acid lakes and pH sensitivity per se does not seem to explain the response of individual species. The relative abundance of Orthocladiinae increased up-core and the long term change may be conceived in terms of a retarded productivity or oligotrophication. The most conspicuous change in the chironomid community appears to coincide with decreasing aluminium concentrations in the sediments and may indicate toxic effects from labile aluminium in the water column.

Le présent travail a été réalisé à partir de récoltes d'insectes aquatiques à la lumière artificielle dans 15 stations du cours axial de la rivière Mouhoun (ex Volta Noire). 12 espèces ont été identifiées. Parmi elles, six sont nouvelles et décrites : Orthotrichia guinkoi n. sp., O. dapola n. sp., O. prevoti n. sp., O. bolyi n. sp., O. mussoi n. sp., O. cazaubonae n. sp. Certaines espèces sont signalées pour la première fois en Afrique de l'Ouest : O. verbekei Jacquemart, O. nova Marlier, O. alboguttata Jacquemart, O. petiti Jacquemart. Deux espèces sont déjà signalées dans la sous-région de l'Afrique occidentale : O. straeleni Jacquemart et O. aequatoriana Kimmins. Pour chaque espèce, le point est fait sur la répartition le long de la rivière étudiée et éventuellement en Afrique.

Une liste de «46» espèces de Chironomidés récoltées pour la première fois en France continentale est présentée. La moitié (22) proviennent des zones potamiques des fleuves Loire et Rhône. Des corrections et des compléments de répartition sont apportés au premier bilan faunistique (Serra-Tosio & Laville 1991). Huit genres Hayesomyia, Dratnalia, Euryhapsis, Gillotia, Kloosia, Lipiniella, Robackia, Saetheria et un sous-genre Demieryptochironomus (Irmakia) sont signalés en France pour la première fois. Ces nouvelles récoltes (+ Parachironomus mauricii et Pseudomittia gracilis), portent à 646 les espèces de Chironomidés actuellement recensées sur le territoire français. Cela correspond à la moitié de la faune chironomidienne paléarctique connue.

L'utilisation des microhabitats par le vairon, Phoxinus phoxinus (L.), le goujon, Gobio gobio (L.) et la loche franche, Barbatula barbatula (L.) a été étudiée en conditions d'étiage d'hiver et d'été dans trois rivières du sud-ouest de la France : l'Ariège, la Nive et le Gave de Pau. Les poissons ont été échantillonnés par pêche électrique selon la méthode de l'Echantillonnage Ponctuel d'Abondance. Onze variables du milieu ont été prises en compte pour décrire l'environnement ponctuel des poissons. Pour chaque rivière, les associations interspécifiques et espèces-variables du milieu ont été calculées et comparées en fonction de la saison. Des variations saisonnières de l'utilisation du microhabitat et des associations interspécifiques ont été observées sur les trois rivières. La nature du substrat et la présence d'abris végétaux jouent un rôle important dans la microrépartition du vairon, du goujon et de la loche franche. Ces structures offrent aux poissons des habitats de refuge et de nutrition privilégiés.