Nectomys apicalis Karyotype: 2n = 42 and FN = 40. Autosomal complement: 20 acrocentric pairs large to very small decreasing in size (ten pairs large to medium-sized, and ten pairs small to very small). Sex chromosomes: X, a medium acrocentric; Y, a small acrocentric (Gardner & Patton 1976, pp. 13, Fig. 6C; Patton et al. 2000). The diploid numbers of 2n = 38 and 2n = 40 were also reported by Gardner & Patton (1976), and Bonvicino & Gardner (2001), respectively. Apparently, these difference in diploid number could be explained by the occurrence of one or two centric fusions. These variation in diploid number occurs in different populations of Brazil, Ecuador and Perú (Table 7, Fig. 11).

Published as part of Moreira, Camila Do Nascimento, Ventura, Karen, Percequillo, Alexandre Reis & Yonenaga-Yassuda, Yatiyo, 2020, A review on the cytogenetics of the tribe Oryzomyini (Rodentia: Cricetidae: Sigmodontinae), with the description of new karyotypes, pp. 1-111 in Zootaxa 4876 (1) on pages 38-39, DOI: 10.11646/zootaxa.4876.1.1, http://zenodo.org/record/4423612