Changes in body shape of the rotifer Keratella quadrata in a pond were recorded over the course of half a year (endof November 1981 to beginning of June 1982). Body and caudal spine lengths increased from November until the endof February, and then decreased until June. Such changes were not significantly correlated consistently positively ornegatively to water temperature, pH, hardness, food levels or copepod numbers. The individuals present during the firsthalf of the study period corresponded most closely to the literature descriptions of the group or subspecies quadrata,while those present during the second half resembled the form, group or variety dispersa. The first half of the studyperiod was characterized by water of relatively low temperature, low pH and high hardness, while, for the second half, temperature and pH increased and hardness decreased.

Stylodrilus curvithecus n. sp., collectée dans un ruisseau de Galice (Espagne), est une espèce proche de S. glandulosus; elle s'en distingue essentiellement par la forme des spermathèques et l'absence de ramifications latérales du vaisseau dorsal dans la région postérieure.Mesenchytraeus lusitanicus n. sp. récoltée dans plusieurs rivières de Galice (Espagne) et du Nord du Portugal est décrite. Une redescription complète de Cognettia hibernica Healy, 1975 à partir de 2 exemplaires récoltés au Portugal permet de compléter la description originale de cette espèce.

Helicopsyche annae sp.n., H. barbata sp.n., H. bifida sp.n., H. jacquemarti sp.n., H. pedunculata sp.n., H. stoltzei sp.n., H. tanzanica sp.n., H. ulugurensis sp.n. and H. usambarensis sp.n. (Trichoptera : Helicopsychidae) are described.All the new species inhabit mountainous areas in eastern Tanzania. Helicopsyche marlieri Jacquemart, 1957 fromeastern Zaïre is redescribed. A key to the species known from East Africa is provided. Distributional and ecologicaldata are discussed and briefly analyzed.

De 1984 à 1991, 114 stations du crénal et de l'épirhithral ont été régulièrement prospectées dans les hauts massifs montagneux du Sud-Ouest de l'Europe (Alpes françaises et italiennes, Pyrénées et principales sierras de la Péninsule Ibérique). Parmi les 33 espèces recensées, peu sont crénophiles : S. (N.) carpathicum, P. (P.) latimucro et S. (N.) oligotuberculatum se développent en très haute altitude ; S. (N.) vernum, S. (N.) brevidens, S. (N.) quasidecolletum et S. (E.) petricolum en haute montagne ; S. (N.) costatum, S. (R.) lamachi et P. (P.) tomosvaryi en moyenne montagne et piémont ; la majorité d'entre elles fréquentent également l'épirhithral. Des espèces peu alticoles dans les Alpes ou les Pyrénées peuvent atteindre des altitudes de plus en plus élevées vers le sud de l'Europe (sierras andalouses en Espagne, Haut-Atlas marocain), par exemple : S (N.) costatum, S. (S.) intermedium, S. (R.) lamachi.

The Holotype of Spaniotoma (Smittia) bilobulata Edwards, 1931 : 299, is redescribed and transferred to the genusPseudosmittia (Goetghebuer) Brundin 1956 emended by Saether 1981. Furthermore P. neobilobulata sp.n. is describedand figured. The genus is first recorded in Argentina.

Pupae and pupal exuviae were collected by drift and hand netting from 27 sites on 10 streams in the Sierra Nevadamountains in 1986 and 1987. The sites represented an altitudinal range from 340 m to 2100 m. The pupal exuviae collections revealed a composite fauna of 143 species. Eukiefferiella (12 spp.) and Tvetenia (3 spp.) were dominant both taxonomically and numerically along most of the altitudinal profile, followed by Cricotopus (11 spp.), Orthocladius (9 spp.) and Diamesa (7 spp.). The altitudinal distribution of the 99 most common species is shown and compared with those obtained in other Europeanstreams or rivers, especially in the Pyrenees. The general pattern of altitudinal zonation shows an increase in speciesrichness from the headwaters (< 2000 m : 58 spp.) toward the middle reaches (1000-1600 m : 121 spp.). The theoreticallyexpected highest species richness in the foothill reaches (> 1000 m : 113 spp.) was not obtained. The periods of reduced or intermittent flow, the domestic organic inputs and the narrowness of the channels in the foothill reaches appear responsible for the decrease of the species richness of the chironomid communities.

Leaf breakdown rates of two species of elm (Ulmus) and two of maple (Acer) were investigated in two low orderstreams located in Western Maryland, U.S.A., and in Northern Appenins, Italy. Within each genus of leaf, one specieswas Italian and one was American. The role of macroinvertebrate shredders in leaf processing was also investigated. In both streams within the same genus of leaf the Italian leaves disappeared faster than the American leaves. Within the same species, the leaves were decomposed more rapidly in the Italian stream. Shredder biomass was always significantly higher on the leaves retrieved from the Italian stream suggesting that shredders had an important role in detritus processing. On the contrary, the comparison between leaf species showed a poor correlation between shredder biomass and leaf breakdown rate. Three hypotheses are proposed. The fact that native leaves were not processed at a faster rate, compared to the exotic leaves, support the notion that shredders do not specialize on litter of a given leaf species, but rather on appropriately conditioned leaf litter regardless of the species. Breakdown rates followed the same rank ordering in each stream : Acer pseudoplatanus > Ulmus minor > Ulmus americana > Acer rubrum indicating the existence of the same hierarchy in the availability of food to macroinvertebrates throughout the year.

A partir de données morphologiques et de mesures de salinité, un modèle numérique de mélange des eaux dans l'estuaire du Bou Regreg a été élaboré. L'estuaire a été divisé en 23 tronçons d'un kilomètre de long pour lesquels le modèle permet de calculer l'évolution dans le temps des salinités moyennes à mi-marée. Au cours de la période étudiée, les échanges entre les 23 tronçons paraissent largement dominés par la dispersion. Le modèle reproduit correctement l'évolution de la salinité après une crue artificielle due à un lâcher de barrage mais également dans d'autres situations.