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Ctenidae represents one of the most representative spider families in the tropical forests of Brazil. Its largest genus,  Ctenus , has approximately 220 species out of the more than 520 Ctenidae species described, and several authors consider it polyphyletic. Chromosomal data are only available for four species of  Ctenus , representing a large gap in the cytogenetic knowledge about the group. This study provided cytogenetic data on two  Ctenus  species and one  Guasuctenus  (previously described as  Ctenus ). All showed 2n♂ = 28 (26+X 1 X 2 0).  Guasuctenus longipes  presented two chromosome pairs containing 18S rDNA genes and  C .  medius , however  C .  ornatus  showed only one chromosome pair with the 18S rDNA gene. Hybridization data using histone H3 probe indicated specific profiles: histone H3 genes were found in one chromosome pair in G.  longipes , in three pairs in  C .  medius , and in four pairs in  C .  ornatus . Furthermore, supernumerary chromosomes were identified in  C .  ornatus  presenting a meiotic behavior similar to that of sex chromosomes; and a trivalent was found in  C .  medius , formed by the association of one sex chromosome and an autosomal bivalent, indicating the importance of these events for the diversification of sex chromosomes in spiders. The C-banding pattern was similar between  C .  medius  and  C .  ornatus  with regard to the number and locations of heterochromatic bands, suggesting that heterochromatin amplification and dispersion, affect karyotypic evolution in the genus. Cytogenetic data showed similarity between  C .  medius  and  C .  ornatus , and differentiation of  G .  longipes  congruent with morphological data. Moreover, although more comparative analyses are needed to specify composition of the dispersed heterochromatin in  Ctenus , the mapping of heterochromatic bands provided insights about the evolution of the karyotypes in this genus.

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Insights on repetitive DNA behavior in two species of Ctenus Walckenaer, 1805 and Guasuctenus Polotow and Brescovit, 2019 (Araneae, Ctenidae): Evolutionary profile of H3 histone, 18S rRNA genes and heterochromatin distribution