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

A study was performed on freshwater gastrotrichs living in the interstitial habitat of some lakes in Latium and of Lake Garda (Italy). Thirty-two chetonotids were collected, twenty-five of which could be identified. Four are new to science (Chaetonotus (Hystricochaetonotus) benacensis, Heterolepidoderma lamellatum, Ichthydium plicatum, l. squamigerum), and two are new to the Italian fauna (Heterolepidoderma macrops, H. majus). The faunistic composition of the lakes is compared with previous data. Interstitial gastrotrichs are less varied and abundant than those of epibenthos and periphyton, but often are of taxonomical and zoogeographical interest. The presence in the interstitial of some epibenthic and periphytic species demonstrates their capacity to colonize 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. Morphological analysis showed a prevalence of small sized animals, with poorly ornamentated cuticular covering and well developed locomotory ciliature, as probable adaptations to interstitial life.