SOME NAIDID OLIGOCHAETES ESTABLISH COMMENSAL RELATIONSHIPS WITH SPECIES OF MOLLUSCS WORLDWIDE. IN THE PRESENT STUDY, WE REPORT THE FINDING OF CHAETOGASTER LIMNAEI IN ILLAPEL RIVER, NORTHERN CHILE. THIS WORM WAS FOUND INHABITING THE MANTLE CAVITY OF THE FRESHWATER GASTROPOD PHYSA ACUTA, AN INVASIVE SPECIES IN THIS COUNTRY. THE TAXONOMIC STATUS OF C. LIMNAEI WAS CONFIRMED BY MOLECULAR ANALYSIS BASED ON MITOCHONDRIAL 16S RIBOSOMAL RNA GENE. RESUMEN LOS OLIGOQUETOS NAIDIDAE PUEDEN ESTABLECER RELACIONES COMENSALES CON ESPECIES DE MOLUSCOS ALREDEDOR DEL MUNDO. EN EL PRESENTE ESTUDIO SE INFORMA EL HALLAZGO DEL OLIGOQUETO CHAETOGASTER LIMNAEI EN EL RÍO ILLAPEL, NORTE DE CHILE. LOS ANIMALES SE ENCONTRARON HABITANDO LA CAVIDAD DEL MANTO DEL GASTERÓPODO DE AGUA DULCE PHYSA ACUTA, UNA ESPECIE INVASORA EN ESTE PAÍS. EL ESTADO TAXONÓMICO DE C. LIMNAEI SE CONFIRMÓ MEDIANTE EL ANÁLISIS MOLECULAR BASADO EN SECUENCIAS DE ADN DEL GEN MITOCONDRIAL DEL ARN RIBOSOMAL 16S.

SPECIES DELIMITATION IN MINUTE FRESHWATER SNAILS IS OFTEN DIFFICULT TO PERFORM USING SOLELY SHELL MORPHOLOGY. THE PROBLEM INTENSIFIES WHEN INVASIVE SPECIES SPREAD WITHIN THE DISTRIBUTION RANGE OF MORPHOLOGICALLY SIMILAR NATIVE SPECIES. IN CHILE, THE TRUNCATELLOIDEAN SNAILS ARE REPRESENTED BY THE NATIVE GENERA HELEOBIA AND POTAMOLITHUS PLUS THE INVASIVE MUDSNAIL POTAMOPYRGUS ANTIPODARUM, WHICH CAN EASILY BE CONFUSED. USING AN INTEGRATIVE APPROACH, WE PERFORMED MOLECULAR PHYLOGENETIC ANALYSIS AND STUDIED REPRODUCTIVE AND MORPHOLOGICAL FEATURES TO IDENTIFY SUPERFICIALLY SIMILAR FORMS INHABITING THE CENTRAL AREA OF THE COUNTRY. TRUNCATELLOIDEAN SNAILS WERE IDENTIFIED IN 40 OF 51 LOCALITIES SAMPLED, 10 CONTAINING POTAMOPYRGUS ANTIPODARUM, 23 HELEOBIA AND 7 POTAMOLITHUS. BASED ON THESE RESULTS AND PREVIOUSLY PUBLISHED DATA, THE KNOWN DISTRIBUTION OF THE MUDSNAIL IN CHILE ENCOMPASSES 6 HYDROLOGICAL BASINS, INCLUDING 18 FRESHWATER ECOSYSTEMS. THE FINDING OF THE MUDSNAILS IN SEVERAL TYPE LOCALITIES OF NATIVE SPECIES/SUBSPECIES OF ""HELEOBIA"" THAT WERE NOT FIND IN SITU SUGGESTS SPECIES REPLACEMENT OR SIGNIFICANT EXTINCTION OF NATIVE FAUNA, A HYPOTHESIS SUPPORTED BY THE RESTUDY OF TYPE MATERIAL THAT SHOWS THAT ENDEMIC FORMS BELONG TO THE GENUS POTAMOLITHUS. THIS STUDY SHOWS THE USEFULNESS OF INTEGRATIVE TAXONOMY NOT ONLY RESOLVING COMPLEX TAXA WITH CRYPTIC MORPHOLOGY BUT ALSO MEASURING THE EXTENT OF AN ONGOING INVASION.

WALTER BIESE DESCRIBED LITTORIDINA SANTIAGENSIS BIESE, 1944 (COCHLIOPIDAE) FROM ESTERO DEHESA IN 1944 BASED EXCLUSIVELY ON EXTERNAL SHELL FEATURES AND A SECOND ALLOPATRIC POPULATION IN YESO SPRING THREE YEARS LATER. SINCE 2011 DIFFERENT SAMPLINGS HAVE BEEN CARRIED OUT AT THE TYPE LOCALITY AND HAVE ONLY PROVIDED SPECIMENS OF THE MORPHOLOGICALLY SIMILAR INVASIVE MUDSNAIL POTAMOPYRGUS ANTIPODARUM GRAY, 1843 (TATEIDAE), RAISING DOUBTS ABOUT THE IDENTITY OF THE SPECIES. THE RECENT FINDING OF TWO SNAIL MORPHOTYPES IN YESO SPRING, A THICK SHELLED FORM CONGRUENT WITH TYPE SPECIMENS OF L. SANTIAGENSIS AND A SLENDER ONE MORPHOLOGICALLY ASSOCIABLE TO P. ANTIPODARUM, ALLOWED COMPARATIVE STUDIES, INCLUDING THE TAXONOMIC ANALYSIS OF ADDITIONAL POPULATIONS WITH SIMILAR SHELL MORPHOLOGY OCCURRING IN CENTRAL CHILE. A DNA BARCODING (COI) APPROACH IDENTIFIED THE SLENDER FORM FROM YESO SPRING IN MAIPO BASIN AND A SECOND POPULATION FROM THE CONTIGUOUS RAPEL BASIN INDEED AS THE INVASIVE P. ANTIPODARUM; HOWEVER, L. SANTIAGENSIS WAS RECOVERED AMONG SPECIES OF POTAMOLITHUS PILSBRY, 1896 (TATEIDAE), JUSTIFYING THE POTAMOLITHUS SANTIAGENSIS (BIESE, 1944) COMB. NOV. BESIDES RECOGNITION OF THREE OTHER POPULATIONS AS BELONGING TO POTAMOLITHUS, THE MOLECULAR ANALYSIS ALSO SUGGESTS TRANS-ANDEAN DISPERSAL OF THIS GROUP OF SNAILS IN THE SOUTHERN CONE OF SOUTH AMERICA.