Revista Brasileira de Zoologia 21 (4): 897–903, dezembro 2004 Compared to other geographical regions, the diversity and distri- bution of continental turbellarians from the Neotropical Region are poorly known. Besides, most of these studies focused, how- ever, on macroturbellarians of the order Tricladida, suborders Paludicola and Terricola (see KAWAKATSU et al. 1992, SEITENFUS & LEAL-ZANCHET in press). Referring to freshwater Neotropical microturbellarians, the studies are scarcer, the MARCUS’ studies (1943, 1944, 1945a, b, 1946, 1949) being very important. More recently, PONCE DE LEÓN (1984, 1986), NOREÑA-JANSSEN (1995), NOREÑA- JANSSEN & FAUBEL (1996) and BRUSA et al. (2003), among others, have increased the knowledge on the diversity and distribution of this group in South-America as showed by NOREÑA et al. (2003). The main purpose of the present work is to report on the results of the first survey of freshwater microturbellarians from Southern Brazil (state of Rio Grande do Sul, Brazil). MATERIAL AND METHODS The sample sites (Fig. 1, Tab. I) were visited once between March and April 2003. Turbellarians were collected by means of a conical hand net (mesh width 335 μm), which was used to sweep through vegetation of the margins of the water bodies. In the laboratory, samples were examined and the micro- turbellarians were extracted for observations in vivo by the method of progressive squash (GAMO 1987a). If necessary for species determination, part of the material was fixed with neu- tral formaline or Bouin (ROMEIS 1989), embedded in Paraplast (Sigma) and sectioned at 5 μm. Sections were stained with Mallory/Cason (ROMEIS 1989). The material was determined based on the taxonomic keys of GAMO (1987b) and YOUNG (2001) as well as by compari- son with the material described by FARÍAS et al. (1995), GAMO & SCHWANK (1987), GAMO & NOREÑA-JANSSEN (1998), LUTHER (1955, 1960, 1963), MARCUS (1945a, b, 1946) and NOREÑA-JANSSEN (1995). RESULTS AND DISCUSSION All species herein reported are cited for the first time for the state of Rio Grande do Sul, Brasil. Two citations, Macrosto- mum johni Young, 1972 and Mesostoma productum (Schmidt, 1848), are the first ones for Brazil, the citation of M. johni be- ing also the first one for the Neotropical Region. Catenulida Meixner, 1924 Catenulidae Graff, 1905 Catenula lemnae Dugés, 1832 Numerous individuals (more than 100) formed by chains of up to 20 zooids (Fig. 2) were collected in one site only (Tab. II). The species was previously recorded by MARCUS (1945a) for the city of São Paulo and vicinities, state of São Paulo, and the vicinities of Curitiba, state of Paraná, Brazil, and by NOREÑA- JANSSEN (1995) for Santa Fé, Argentina. This is the fourth record for the Neotropical Region and the third one for Brazil. Freshw eshw eshw eshw eshwater micr ater micr ater micr ater micr ater microturbellar oturbellar oturbellar oturbellar oturbellarians (Platyhelminthes) fr ians (Platyhelminthes) fr ians (Platyhelminthes) fr ians (Platyhelminthes) fr ians (Platyhelminthes) from Rio Gr om Rio Gr om Rio Gr om Rio Gr om Rio Grande do Sul, ande do Sul, ande do Sul, ande do Sul, ande do Sul, Br Br Br Br Brazil azil azil azil azil Jacinto Gamo 1 & Ana Maria Leal-Zanchet 2 1 Departamento de Biología Animal, Universidad de Alcalá. Ctra. N-II, Km 33,6, 28871 Alcalá de Henares, Madrid, Spain. E-mail: jacinto.gamo@uah.es 2 Instituto de Pesquisas de Planárias, Universidade do Vale do Rio dos Sinos. Avenida Unisinos 950, 93022-000 São Leopol- do, Rio Grande do Sul, Brasil. E-mail: zanchet@bios.unisinos.br ABSTRACT. Ten species of freshwater microturbellarians of three ordens, Catenulida, Macrostomida and Rhabdocoela, were collected in seven sites situated in the Northeast region of Rio Grande do Sul, Brazil. Two species, Macrostomum johni Young, 1972 and Mesostoma productum (Schmidt, 1848), are cited for the first time for Brazil, the citation of M. johni being also the first one for the Neotropical Region. All species are cited for the first time for the state of Rio Grande do Sul. KEY WORDS. Neotropical, new records. RESUMO. Dez espécies de microturbelários dulciaqüícolas, pertencentes a três ordens, Catenulida, Macrostomida e Rhabdocoela, foram coletados em sete localidades situadas no Nordeste do estado do Rio Grande do Sul, Brasil. Duas dessas espécies, Macrostomum johni Young, 1972 e Mesostoma productum (Schmidt, 1848), são registradas pela primeira vez para o Brasil, sendo o registro de M. johni o primeiro também para a Região Neotropical. Todas as espécies são registradas pela primeira vez para o estado do Rio Grande do Sul. PALAVRAS CHAVE. Neotropical, novos registros.