A review on the cytogenetics of the tribe Oryzomyini (Rodentia: Cricetidae: Sigmodontinae), with the description of new karyotypes Author Moreira, Camila Do Nascimento Author Ventura, Karen Author Percequillo, Alexandre Reis 0000-0001-9490-5457 cmoreirabio@gmail.com Author Yonenaga-Yassuda, Yatiyo text Zootaxa 2020 2020-11-06 4876 1 1 111 journal article 7983 10.11646/zootaxa.4876.1.1 4ee8b608-7c73-4980-9e86-3e3719e91c7f 1175-5326 4423612 190EC586-E14B-4AEF-A5EF-3DA401656159 Euryoryzomys sp. nov. A new karyotype for the genus was described by Silva et al . (2000) . Karyotype: 2n = 76 and FN = 86. Autosomal complement: six metacentric pairs (two large and four small), and 31 acrocentric pairs decreasing in size from large to small. Sex chromosomes: X, a large subtelocentric; Y chromosome presented two different morphologies, a medium submetacentric (Ya), and a medium acrocentric (Yb). C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of all autosomes. The short arm of X and the entirely Y chromosome were heterochromatic. G-banding was also performed. Multiple NORs, varying from four to nine were localized at the telomeric regions of the short arms of small acrocentric chromosomes. FISH with telomeric sequences revealed signals exclusively at the ends of all chromosome arms and no interstitial signals were observed ( Silva et al . 2000 , pp. 220, Fig. 1 ). According to the authors, the karyotype of E. macconnelli (2n = 76, FN = 85) from Venezuela ( Musser et al . 1998 ) was different from Euryoryzomys sp. nov. , because in the former there was no large metacentric chromosomes, and there was five metacentric small pairs while in the latter karyotype, two large metacentrics was observed as well as four small metacentric pairs. Sex chromosomes was also distinctive between both karyotypes ( Silva et al . 2000 ). We present a different karyotype for the genus, here referred as Euryoryzomys sp. The cytogenetic analysis was performed for three males collected in Rio Japurá, Amazonas, Brazil ( Table 1 ).