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Higher TaxaColubridae (Dipsadinae), Colubroidea, Caenophidia, Alethinophidia, Serpentes, Squamata (snakes)
Common Names 
Atractus albuquerquei — ZAHER et al. 2005:32 (in part) 
DistributionBrazil (Mato Grosso: Parecis Plateau and adjacent areas)

Type locality: Bocaiúva (12°29’50’’S, 57°52’30’’W; ca. 312 m), Craveri River, municipality of Brasnorte, state of Mato Grosso, Brazil.  
TypesHolotype: MNRJ 26734 (formerly UFMT 8139), adult male, collected in 2009 by Universidade Federal de Mato Grosso team during the faunal rescue operation for the construction of a small hydroelectric plant; Paratypes: Nine specimens, all from the state of Mato Grosso, Brazil: UFMT 8137 (adult female), UFMT 8138 (adult male), UFMT 8140 (juvenile female), UFMT 8141 (juvenile male), UFMT 8142 (juvenile male) same data as the holotype; an adult female, UFMT 3949, collected by M. Carvalho on May 2004, specimen found in the stomach of a Pseudoboa coronata (UFMT 3726), from Continental Farm (11°30’06’’S, 55°12’18’’W; ca. 350 m), municipality of Claudia; an adult female, MNRJ 26735 (formerly UFMT 9024),collectedbyR.A ́vilaandR.Kawashita-Ribeiroon18 January 2011 at Vale de São Domingos (coordinates in paper; ca. 500 m), municipality of Jauru ́; a juvenile female, UFMT 9116, collected on 3 March 2011 by R. Kawashita-Ribeiro at Jurena River, Sa ̃o Nicolau Farm (098510S, 588140W; ca. 220 m); an adult female, MZUSP 20667, collected on 17 October 2012 by JGP Consultoria Ambiental team in the faunal rescue operation for the construction of a small hydroelectric plant at Segredo (coordinates in paper; ca. 500 m), Juruena River, municipality of Sapezal. 
DiagnosisDiagnosis: Atractus stygius can be distinguished from allcongenersbythefollowingcombinationofcharacters:(1) smooth dorsal scale rows 15/15/15; (2) postoculars two; (3) loreal moderately long; (4) temporal formula usually 1þ2; (5) supralabials seven, third, and fourth contacting eye; (6) infralabials seven, first four contacting chinshields; (7) maxillary teeth seven; (8) gular scale rows usually four; (9) preventrals usually four; (10) ventrals 178–192 in females, 170–176inmales;(11)subcaudals20–23infemales,25–28 in males; (12) in preservative, dorsum dark brown to black except for a conspicuous pale brown to beige parietal band; (13) in preservative, ventral surface of body cream, heavily pigmented with black marks, to mostly black; (14) maximum body size moderate in females (470 mm SVL) and males (390 mm SVL); (15) tail size small in females (8.0–9.7% SVL) and in males (8.1–10.4% SVL); (16) hemipenis moderately bilobed, semicapitate, and semicalyculate.

Comparisons: Among all congeners, Atractus stygius shares only with A. albuquerquei, A. caete, A. emmeli, and A. reticulatus the following combination of morphological characters: dorsal scales smooth, rows 15/15/15; frontal shield broader than long; nostril longer than prenasal; maxillary bone with a well-developed lateral process and no projection at the level of the last teeth; maxillary teeth six to eight; hemipenis moderately bilobed, semicapitate, and semicalyculate; dorsum ground color dark brown to uniformly black (see Discussion). Atractus stygius differs from A. albuquerquei and A. reticulatus by having a conspicuous pale parietal band in adult specimens, belly frequently heavily pigmented with black marks, usually seven upper and lower labial scales, absence of naked pocket on hemipenis, and 170–176 ventrals in males and 178–192 in females, 20– 23 subcaudals in females and 25–28 in males (vs. absence of parietal band in adult specimens [in A. reticulatus], venter frequently uniformly cream, usually six upper and lower labial scales, presence of naked pocket on the proximal region of hemipenis, and 192–211 ventrals in females and 170–184 in males, 27–38 subcaudals in females and 37–44 in males of A. albuquerquei; and venter uniformly cream, infralabials, 27–38 subcaudals in females and 37–44 in males of A. reticulatus). Atractus stygius differs from A. caete by having four gular scale rows and conspicuous parietal band (vs. three gular scale rows and absence of parietal band). Atractus stygius differs from A. emmeli in having 170–176 ventrals in males and 178–192 in females; CL/SVL 8.1– 10.4% in males, 8.0–9.7% in females; hemipenis moderately bilobed and centrolinearly oriented with shallow spinulate calyces, well-defined capitular groove, and narrow sulcus spermaticus (vs. 147–169 in males and 154–187 in females; CL/SVL 9.2–14.7 in males, 5.7–9.6% in females; organ with slightly bilobed and centrifugally oriented lobes covered with huge developed spinulate calyces, comprising deep projections, indistinct capitular groove, and laterally expanded sulcus spermaticus in A. emmeli).
Atractus stygius also differs from the other cis-Andean congeners with 15/15/15 dorsal scale rows, except A. occipitoalbus Jan 1862 and A. orcesi Savage 1955, by dorsum uniformly black in preservative (vs. dorsum in preservative cream to light brown with dark marks but never uniformly black in A. boimirim Passos, Prudente, and Lynch 2016; A. edioi Silva, Silva, Ribeiro, Souza, and Souza 2005; A. insipidus Roze 1961; A. paraguayensis Werner 1924; A. potschi Fernandes 1995; A. punctiventris Amaral 1933; A. tartarus Passos, Prudente, and Lynch 2016; or black with conspicuous paired white dots in A. avernus Passos, Chiesse, Torres-Carvajal, and Savage 2010 or beige spots or blotches in A. tamessari Kok 2006). Atractus stygius differs from A. occipitoalbus and A. orcesi by having seven suparalabials, two postoculars in females, and 170–176 ventrals in males and 178–192 in females and 25–28 in males, 20–23 subcaudals in females (vs. usually eight supralabials in both species; usually single postocular in females of A. occipitoalbus; 129–155 ventrals in males, 143–172 in females and 20–26 subcaudals in males, 9–17 in females of A. occipitoalbus; and 134–152 ventrals in males, 142–158 in females and 18–34 subcaudals in males, 13–22 in females). 
CommentSimilar species: Atractus albuquerquei; Possible misidentification: MZUSP 11157, 11242, fide Passos et al. 2019. 
EtymologyThe specific epithet stygius is a Latin adjective meaning of hell or the underworld. The word is also used in reference to something pernicious or tragic. We employed this name because of the secretive habits of the new species as well as an urgent alert for the absurd levels of deforestation that the Cerrado savannas have suffered in recent years, as a result of the indiscriminate expansion of soybean monoculture (Boerema et al. 2016). This scenario is even more worrisome for the conservation agenda given the growing disregard of Brazilian authorities regarding the preservation of natural environments, and considering the previously undetected high levels of herpetofaunal endemism recently reported for the Cerrado (Nogueira et al. 2011; Azevedo et al. 2016; Guedes et al. 2017). 
  • 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, Paulo; Josué A.R. Azevedo, Cristiano C. Nogueira, Ronaldo Fernandes, and Ricardo J. Sawaya 2019. An Integrated Approach to Delimit Species in the Puzzling Atractus emmeli Complex (Serpentes: Dipsadidae). Herpetological Monographs 33 (1): 1-25 - get paper here
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