Atractus latifrons is a semi-fossorial snake diagnosed by the following set of characters: 17/17/17 smooth dorsal scales without apical fossae; five maxillary teeth; small eyes; frontal wider than long compared to supraocular; loreals large and wide; absence of preocular; postoculars (1/1); supralabials (6/6); entire anal plate; short tail. It occurs in tropical forests of Colombia, Venezuela, Peru, French Guiana, Suriname and in Brazil, in the following states: Amazonas, Acre, Rondônia, Manaus, Pará, Mato Grosso and western Maranhão. Although some authors have tried to explain the chromatic variation and possible mimicry of A. /atifrons with true coral species, information on this subject is still insufficient to understand the behavior and to know the chromatic patterns described for this species. In this context, the present work aims to analyze the morphological variations (external and internal characters) present in A. /atifrons, relating them to their chromatic and geographical variations, in addition to analyzing the mimetic behavior with some species of true corals of the genus Micrurus. We analyzed 59 specimens of A. /atifrons deposited in the herpetological collections of the Museu Paraense Emílio Goeldi (MPEG), Museu de Zoologia da Universidade de São Paulo (MZUSP) and Universidade Federal do Mato Grosso (UFMT). Four variations were identified for the Bicolor and Tricolor patterns of A./atifrons, being the following: Monadal bicolor, Monadal tricolor, Tricolor in dyads and Tricolor in triads. Such patterns mimic the following sympatric species of the genus Micrurus: Monadal bicolor: M. a/bicinctus; Monadal Tricolor: M. /angsdorffi, M. avery and M. ornatissimus and with Tricolor pattern in triads: M. fi/iformis, M. /emniscatus ssp., M. hemprichii ssp. The specimens analyzed showed significant sexual dimorphism for the number of subcaudal and ventral scales and tail length, where the mean number of ventral scales was higher for females, and the mean number of subcaudal scales and tail length were higher for males. Analysis of hemipenial morphology showed that there is a difference in lobe size between Tricolor patterns in dyads (longer lobes) and Monadal bicolor (smaller lobes).
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