Morphological examination of novel specimens of paruterinid cestodes from passerine birds from Brazil and Chile and of museum specimens from Paraguay revealed two new species: Anonchotaenia prolixa sp. n. from Elaenia albiceps chilensis Hellmayr from Chile, and Anonchotaenia vaslata sp. n. from Tyrannus melancholicus (Vieillot) (type host) and Myiodynastes maculatus (Statius Muller) from Paraguay. The generic diagnosis of Anonchotaenia Conn, 1900 is amended, prompted by the presence of the armed cirrus and the elongated cirrus sac of A. prolixa. Two species were redescribed: Anonchotaenia brasiliensis Fuhrmann, 1908 from Tachyphonus coronatus (Vieillot) and Thraupis cyanoptera (Vieillot) (new host records) from Brazil, and Thraupis sayaca (Linnaeus) and Volatinia jacarina (Linnaeus) from Paraguay (new host and geographic records); and Anonchotaenia macrocephala Fuhrmann, 1908 from Tachycineta leucorrhoa (Vieillot) (new host record) from Brazil, Tachycineta meyeni (Cabanis) from Chile (new host and geographic record) and Stelgidopteryx ruficollis (Vieillot) from Paraguay (new host and geographic record). Scanning electron microscopy of A. brasiliensis and A. macrocephala revealed less microthrix variation than has been reported for other cyclophyllidean taxa. Sequence data were generated for nuclear ssr-and lsr-DNA and mitochondrial rrnL and cox1 for A. prolixa, A. brasiliensis, and A. macrocephala. Maximum likelihood and Bayesian inference analyses supported each species as distinct, but revealed cryptic diversity among A. brasiliensis specimens from different host families. New host records of A. brasiliensis and A. macrocephala prompted a formal assessment of host specificity. Anonchotaenia prolixa was found to be oioxenous (HS S = 0), A. vaslata and A. macrocephala were found to be metastenoxenous (HS S = 3.000 and 3.302, respectively), whereas A. brasiliensis was found to be euryxenous (HS S = 5.876). Anonchotaenia brasiliensis has been found parasitising several species of different passerine families that participate in mixed-species foraging flocks in the Atlantic Forest. A diversity of species of other families join these flocks and are among the substantial number of South American passerine species yet to be examined for cestodes. South American Anonchotaenia species are poorly known, with only six species in total reported from the continent and all but two of these species described with brief treatments prior to 1909 (Fuhrmann 1901(Fuhrmann , 1908. As part of the present study, fieldwork conducted near the Comau Fjord, Chile in 2008 and near São Paulo, Brazil in 2011 led to the collection of cestode specimens from a diversity of avian orders, but predominantly Passeriformes. Examination of this material combined with the study of museum specimens resulted in the description of two new species of Anonchotaenia as well as the redescription of Anonchotaenia brasiliensis Fuhrmann, 1908 and Anonchotaenia macrocephala Fuhrmann, 1908. Anonchotaenia brasiliensis and A. macrocephala are the first ...
