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Atractus natans HOOGMOED & PRUDENTE, 2003

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Higher TaxaColubridae (Dipsadinae), Colubroidea, Caenophidia, Alethinophidia, Serpentes, Squamata (snakes)
Common Names 
SynonymAtractus natans HOOGMOED & PRUDENTE 2003
Atractus emersoni SILVA HAAD 2004
Atractus emersoni — PASSOS et al. 2007
Atractus natans — PASSOS et al. 2007
Atractus natans — WALLACH et al. 2014: 77
Atractus natans — NOGUEIRA et al. 2019 
DistributionBrazil (Amazonas, Pará), Peru (Loreto)

Type locality: near flutuante at confluence of Paraná Apara and Rio Mamirauá, Estação Ecológica de Mamirauá, Município de Uarini, Amazonas, Brazil, 3°02’57.2”S 64°50’59.7”W, 50 m elevation.

emersoni: Colombia (Amazonas), Brazil; Type locality: Boa Vista-Brasil. Municipio de Benjamín Constant, en la rivera del río Solimoes, situada a 4º, 25’ de latitud sur y a 70º de longitud oeste.  
TypesHolotype: MPEG 18836
Holotype: ICN-MHN = ICN 10097 [emersoni] 
DiagnosisDescription: is small (maximum total length 308 mm) with a coniform head, has 17-17-17 smooth dorsals, without apical pits, male lacking pre-anal keels, ventrals 136-162, caudals 19-25, anal undivided. One or two postoculars, loreal 1.6 –2.8 times as long as high, frontal triangular, wider than long. Maxillary teeth 5-6. The hemipenis is bilobed, with bifurcated sulcus spematicus, capitulum with calyces covered by very small spines, body covered by spines of different size. The back is (dark) brown without a distinct pattern, although on the flanks small darker spots more or less in longitudinal rows are present, a light collar on the posterior part of the head, (indications of) a light area on the snout, throat with black spots sometimes arranged in oblique lines, a wide median black band on the white (in life partly brick red) belly, and underside of tail dark with light spots (brick red in life) at the posterior end of the scales.

Diagnosis.- A small species of Atractus (maximum svl 283 mm in females, 221 mm in the male, tail length 25 mm in females, 32 mm in the male) with a narrow, distinctly coniform head, with 17-17-17 smooth dorsal scales without pits, 153-162 ventrals in females, 136 in the single male, 19-21 pairs of subcaudals in females, 25 in the single male, a frontal that is wider than long to as wide as long, loreal 1.6-2.8 times as long as high, no preocular, one (rarely) or two (mostly) postoculars, a small anterior and a long upper posterior temporal scale which is bordered ventrally by three lower posterior temporals. A wide and very narrow, small mental. Snout light, more so in the juvenile than in adults. A light collar on the back of the head and a wide black median ventral band of varying width on a white (or orange in life) background, underside of tail black, but with light edges or white (orange in life) spots on the scales. The new species can be distinguished from other species of Atractus in the region by the following combination of characters: its colour pattern, frontal as wide as long or wider, 136 (male) or 153-162 (females) ventrals, low number of subcaudals (females: 19-21, male: 25), no apical pits and very short tail (8.1-8.5% of total length in females, 12.6% in the male). A. albuquerquei, A. elaps, A. insipidus, A. poeppigi and A. trilineatus can be distinguished from A. natans by only having 15 dorsal scale rows. A. favae is easily distinguished from all other Atractus in the region (or any other Atractus for that matter), including A. natans, by having the mental in contact with the single pair of chin shields, by having a tail that is about 25% of the total length and having a very high number of subcaudal scales ( 57-67). Adult A. natans are much smaller than A. badius, A. flammigerus, A. latifrons, A. major, A. snethlagae and A. torquatus, who also have 17 dorsals. From A. alphonsehogei, A. schach and A. zidoki it can be distinguished on the basis of dorsal and ventral patterns, the lighter snout and wide light band on the back of the head, and from A. alphonsehogei and A. zidoki also by lacking apical pits and (in males) lacking keels on the scales of the flanks in the anal region (from HOOGMOED & PRUDENTE 2003). Updated diagnosis in Passos et al. 2012: 385.

Diagnosis (emersoni): “Especie de tamaño mediano, coloración rojo oscuro de fondo, ornado con manchitas negras, algunas triangulares, otras cuadradas o circulares, ocupan una o dos escamas dorsales en las caras superiores y laterales del cuerpo. Vientre con franjas transversales, color marrón o castaño oscuro localizadas en cada una de las gastrotegas. Regiones laterales del abdomen, anaranjado; ventrales 156, subcaudales 25, supralabiales 7-7, infralabiales 6-6.” 
CommentSynonymy: Passos et al (2012) synonymized A. emersoni with A. natans. 
EtymologyNamed after Latin “natans” = floating, in loose reference to the fact that all specimens collected in Mamirauá (the majority of the type series) were found in floating rotten logs in flooded forest.

Etymology (emersoni): “Dedicada en homenaje al Dr. Helio Emerson Belluomini, del Instituto Butantan, en reconocimiento a su valiosa contribución al estudio de las serpientes venenosas del Brasil, a la producción media de veneno y la determinación de la potencia letal de éstos, en animales domésticos.” 
  • Hoogmoed, M. S.; Prudente, A. L. C. 2003. A new species of Atractus (Reptilia: Ophidia: Colubridae: Dipsadinae) from the Amazon forest region in Brazil. Zoologische Mededelingen 77 (15/36): 425-440 - get paper here
  • Nogueira, Cristiano C.; Antonio J.S. Argôlo, Vanesa Arzamendia, Josué A. Azevedo, Fausto E. Barbo, Renato S. Bérnils, Bruna E. Bolochio, Marcio Borges-Martins, Marcela Brasil-Godinho, Henrique Braz, Marcus A. Buononato, Diego F. Cisneros-Heredia, 2019. Atlas of Brazilian snakes: verified point-locality maps to mitigate the Wallacean shortfall in a megadiverse snake fauna. South American J. Herp. 14 (Special Issue 1):1-274 - get paper here
  • Passos, P. & Fernandes, R. 2008. A new species of the colubrid snake genus Atractus (Reptilia: Serpentes) from the central Amazon of Brazil. Zootaxa 1849: 59–66 - get paper here
  • Passos, P., R. Fernandes and Borges-Nojosa, D.M. 2007. A New Species of Atractus (Serpentes: Dipsadinae) from a Relictual Forest in Northeastern Brazil. Copeia 2007 (4): 788–797 - get paper here
  • Passos, Paulo; Diego Cisneros-Heredia, Dani Enrique Rivera, Cesar Aguilar, and Walter E Schargel 2012. Rediscovery of Atractus microrhynchus and Reappraisal of the Taxonomic Status of A. emersoni and A. natans (Serpentes: Dipsadidae). Herpetologica 68 (3): 375-392. - get paper here
  • Silva Haad, J.J. 2004. Las serpientes del género Atractus Wagler, 1828 (Colubridae; Xenodontinae) en la Amazonia colombiana. [The snakes of the genus Atractus Wagler, 1828 (Colubridae; Xenodontinae) in the colombian Amazonia.]. Revista de la Academia Colombiana de Ciencias Exactas, Físicas y Naturales (108): 409-446
  • Wallach, Van; Kenneth L. Williams , Jeff Boundy 2014. Snakes of the World: A Catalogue of Living and Extinct Species. [type catalogue] Taylor and Francis, CRC Press, 1237 pp.
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