This study describes two new species of the genusEchinogammarusfrom springs and rivers located in northern Tunisia. These two species are related to theEchinogammarus simoni-group, but differ from those species in terms of several characteristics, such as a 3-articulated accessory flagellum of the first antennae, the lack of a dense setation on the second antennae, the presence of lateral setae on the telson and the lack of plumose setae on uropod 3. The first species,Echinogammarus carthaginiensisn. sp., is easily distinguishable from the second,Echinogammarus tunetanusn. sp., by the setation on the mandibular palp and gnathopods and the relative length of uropods 1 and 3. A full description of the two new species and information about their distribution is given in this paper.

Northern Africa, although one of the world hotpots of biodiversity, is poorly studied and the freshwater fauna living in this part of the world remains partly unknown. This study focused on the diversity and distribution of the poorly known epigean freshwater amphipods. We performed an exhaustive analysis of the literature on this group of crustaceans and sampled 106 additional localities from the eastern part of Algeria and in Tunisia. Our results showed an important diversity with 25 species (including the presence of at least three new undescribed species) and a very high rate of endemism with 52% of species occurring at on only 1 or 2 sites. We also highlighted a very low diversity on each site with only 4.4% of sites harboring more than 1 species. The comparative distribution of certain species between Europe and Maghreb and also between the western and eastern part of Northern Africa allow us to discuss some hypotheses about the factors underlying this endemism and the biogeographical origin of species. However, our study revealed a general lack of knowledge in the region, especially in the South of Morocco and Algeria. Hence, more information would be needed to propose adapted conservation strategies of freshwater fauna in Maghreb.

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Reproductive biology and population dynamics of the freshwater shrimp, Atyaephyra desmarestii were studied in Tunisia. In the reserve dam lake of Sidi Salem (northern Tunisia), a total of 7200 specimens was collected in monthly sampling over two years, from August 1996 to July 1998. Each sample of shrimps was sorted in the laboratory and separated into juveniles, males, and females.The presence of ovigerous females during spring and summer indicated that reproduction of Atyaephyra desmarestii is seasonal, starting in March and ending in August, followed by a sexual rest of six months, from September to February. The peak of reproductive females occurred in April and undifferentiated juveniles were present over the year.Fecundity was positively correlated with the size of ovigerous females. The sex-ratio underwent seasonal and monthly fluctuations, related to the size of the shrimp. Females were less numerous than males between 15 and 20 mm, but dominated beyond 20 mm.Analysis of the size-frequency distribution allowed to identify ten cohorts, four in the first sample of August 1996, and the other six during the rest of the sampling period. Life span was estimated between 13 and 16 months, based on 2 cohorts per season, one in spring and the other in summer. Cohorts appearing in May of each year, quickly reached sexual maturity and became reproductive after three months at just 17-18 mm total length. RÉSUMÉ La biologie de la reproduction et la structure de taille d'une population de la crevette d'eau douce Atyaephyra desmarestii font l'objet d'une étude menée en Tunisie. Dans la retenue du barrage Sidi Salem (nord de la Tunisie), un total de 7200 individus a été prélevé au cours d'échantillonnages mensuels effectués pendant deux années consécutives, d'août 1996 à juillet 1998. Chaque échantillon de crevettes, ramené au laboratoire, a été trié et les différentes catégories ont été séparées en indifférenciés, mâles et femelles. )La présence de femelles ovigères au printemps et en été indique que la reproduction de cette espèce est saisonnière. Elle commence au mois de mars et se termine en août. Elle est suivie d'une période de repos sexuel de 6 mois, de septembre à février. Le pic de présence des femelles reproductrices a lieu en avril. Les jeunes indifférenciés sont présents durant toute l'année.La fécondité est corrélée positivement avec la taille des femelles ovigères. Quant au sex-ratio, il présente des fluctuations mensuelles et saisonnières en relation avec la taille totale de la crevette. En effet, les femelles sont moins nombreuses que les mâles pour une taille comprise entre 15 et 20 mm, alors qu'elles dominent au-delà de 20 mm.L'analyse des distributions des fréquences de taille a permis la détermination de dix cohortes dont quatre ont été identifiées dans le premier échantillon d'août 1996 et les six autres durant le reste de la période d'étude. Le suivi d'une cohorte printanière et d'une cohorte estivale a permis d'estimer la durée de vie de cette espèce qui varie entre 13 et 16 mois. Les cohortes qui a...

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