New report for Pristinella jenkinae Stephenson, 1931 (Annelida: Oligochaeta: Naididae) geographical distribution from Southern Caspian Sea basin, Mazandaran province - Iran

Pristinella jenkinae (Stephenson, 1931) is a freshwater cosmopolitan oligochaete. This species was found during limnological investigation in two rivers alongside Iranian coasts and has not been previously reported from Iran‟s freshwater fauna and Southern Caspian Sea basin. The specimens of P. jenkinae were collected bimonthly from Cheshmehkileh and Sardabrood rivers and estuaries (river mouth) using a Van Veen grab (0.03 m2) and Surber (0.1 m2, 0.2 mm-mesh size) samplers at three stations in each estuary (S1: riverine, S2: estuary and S3: marine ecosystem) with three replicates from November 2014 through September 2015. Results of temporal distribution showed that the highest and lowest density and biomass of this species were in January (102.3±68.3 ind m-2 and 0.075±0.034g m-2) and in September (24.4±12.3 ind m-2 and 0.020±0.005g m-2), respectively which were significantly different (N=57, t=0.99, p<0.05). Spatial distribution of P. jenkinae among sampling stations (S1, S2 and S3) showed significant differences (N=57, t=0.99, p<0.05). Freshwater stations (S1) within the river showed higher density and biomass (112.1±64.8 ind m-2 and 0.082±0.035g m-2) than semibrackish stations (S2) within the estuary (18.8±10.3 ind m-2 and 0.013±0.005g m-2). Semi-brackish stations (S2) showed higher density and biomass than brackish stations (S3) within the sea (0±0 ind m-2 and 0±0g m-2). Density and biomass of this species in Cheshmehkileh River and estuary was more than Sardabrood. A significant correlation (N=57, r=Pearson, p<0.05) between density and biomass of P. jenkinae with environmental variables was found.