GASTROTRICHS FROM INTERSTITIAL FRESH-WATER, WITH A DESCRIPTION OF 4 NEW SPECIES

A study was performed on freshwater gastrotrichs living in the interst itial habitat of some lakes in Latium and of Lake Garda (Italy). Thirt y-two chetonotids were collected, twenty-five of which could be identi fied. Four are new to science (Chaetonotus (Hystricochaetonotus) benac ensis, Heterolepidoderma lamellatum, Ichthydium plicatum, l. squamiger um), and two are new to the Italian fauna (Heterolepidoderma macrops, H. majus). The faunistic composition of the lakes is compared with pre vious data. Interstitial gastrotrichs are less varied and abundant tha n those of epibenthos and periphyton, but often are of taxonomical and zoogeographical interest. The presence in the interstitial of some ep ibenthic and periphytic species demonstrates their capacity to coloniz e ecologically different habitats. The grain size of the substrate was not clearly correlated with faunal richness, but there was a possible influence of the amount of the organic detritus in the sediment. Morp hological analysis showed a prevalence of small sized animals, with po orly ornamentated cuticular covering and well developed locomotory cil iature, as probable adaptations to interstitial life.