The polychaete Nereis falsa Quatrefages, 1866 is present in the area of El Kala National Park on the East coast of Algeria. Field investigations were carried out from January to December 2007 to characterize the populations' reproductive cycle, secondary production and dynamics. Reproduction followed the atokous type, and spawning occured from mid-June to the end of August/early September when sea temperature was highest (20-23°C). The diameter of mature oocytes was approximately 180 lm. Mean lifespan was estimated to about one year. In 2007, the mean density was 11.27 ind. m -2 with a minimum of 7.83 ind. m -2 in April and a maximum of 14.5 ind. m -2 in February. The mean annual biomass was 1.36 g m -2 (fresh weight) with a minimum of 0.86 g m -2in December and a maximum of 2.00 g m -2 in June. The population consisted of two cohorts distinguishable from size frequency distributions. One cohort corresponded to the recruitment of 2006 and the other appeared during the study period in September 2007. The annual production of N. falsa was 1.45 g m -2 year -1 , and the production/biomass ratio was 1.07 year -1 .

We studied the effects of one ecdysteroid analog (RH-0345) on the ovarian and testicular components of the centipede Eupolybothrus nudicornis used as a model of predators of soil fauna. The injection of 10 µg of RH-0345 significantly reduced protein, lipid and carbohydrate concentrations in both the ovarian tissue of females and testicular tissue of males collected in spring or autumn. In consequence, this study shows that ecdysteroid analog pesticides can affect the reproduction of other arthropods than insects by modifying the level of metabolites in male and female gonads.

Four species of nereidid polychaetes, Peri ner eis cultrifera, P. macropus, Nereis falsa, and Platy ner eis dumerilii, were identified during three years in four intertidal rocky shore sites (El-Kala, Annaba, Skikda and Collo) along the east coast of Algeria during the years 2011-2013. Species' distribution fluctuated according to sites and season. Perinereis cultrifera was observed during most of the year, except in summer. Perinereis macropus was observed at El-Kala, Skikda and Collo mainly in late winter and early spring. Nereis falsa was observed during most of the year in El-Kala and Annaba; this species was also observed in Skikda in 2011 but then disappeared in the last two years of this study. Finally, the presence of P. dumerilii was noticed only in El-Kala for a few months (mainly in March and April). Perinereis cultrifera, P. macropus and P. dumerilii reproduce after acquiring the epitokous form between April and May, when surface seawater temperature starts rising. The largest mature oocytes were about the same for P. cultrifera (279 µm) and P. macropus (278 µm), while this value was smaller for P. dumerilii (166 µm). In contrast to the other three species of nereidid polychaetes, N. falsa reproduces without epitokal modification between July and August when sea temperature was highest. The largest mature oocytes (168 µm) are about the same as P. dumerilii but is much small than those of P. cultrifera and P. macropus.