Holotype: UFMT-R 8512, adult male, collected on 27 October 2009 by Carolina L. Cavlac.
Diagnosis. Helicops apiaka sp. nov. is distinguished from all congeners by the following combination of characters: (1) dorsal scales in 21/21/19 rows in males and 23/21/19 rows in females; (2) subcaudals 79–103 (n = 14; 95.1 +/- 5.8) in males and 80–84 (n 1⁄4 8; 82.4 6 1.3) in females; (3) ventrals 118–127 (n = 18, 121.2 +/- 2.2) in males and 124–132 (n = 8, 126.9 +/- 2.5) in females; (4) subcaudal keels present; (5) maxillary teeth 15–16 + 2; (6) infralabials 9–12/10–11; (7) dorsal scales strongly keeled; (8) banded dorsal color pattern; (9) ventral blotches 14–19 (n = 18, 15.9 +/- 1.4) in males and 16–19 (n=8, 17 +/- 0.9) in females.
Can be distinguished easily from H. danieli, H. hagmanni, H. leopardinus, H. pastazae, H. petersi, H. polylepis, H. scalaris, and H. yacu by having a banded (instead of spotted) dorsal color pattern and by the presence of subcaudal keels (absent in these species, except in H. scalaris and H. yacu; Rossman in Peters and Orejas–Miranda, 1970). Furthermore, the new species can be distinguished from H. danieli by a higher number of dorsal and subcaudal scales (19– 21/19–20/16–19 dorsal scales in males and females, 76–86 subcaudals in males, and 61– 70 subcaudals in females of H. danieli; Yuki, 1994; Rossman, 2002b) and by its ventral color pattern (cream venter with two rows of black semicircular markings in H. danieli; Rossman, 2002b). From H. hagmanni, H. pastazae, H. polylepis and H. yacu, the new species is further distinguished by a smaller number of dorsal scale rows (23–27/27–29/19–23 in males and 27/27/21 in females of H. hagmanni [Rossman, 1975]; 23/24/19 in H. pastazae [Rossman, 1976]; 23/23/19 in both sex of H. polylepis [Dixon and Soini, 1986]; 23–29/25– 28/18–20 in females of H. yacu [Rossman and Dixon, 1975; Rossman and Abe, 1979]). From H. leopardinus, the new species is also distinguished by a generally higher number of subcaudals (75.9 +/- 4.1, range 67–86, n = 52 in males and 62.7 +/- 4.9, range 53–76, n = 40 in females of H. leopardinus), and a smaller number of maxillary teeth (18 + 2 in both sexes of H. leopardinus). The new species lacks the three nuchal bands present in H. scalaris (Rossman, 2002a).
From H. carinicaudus, H. infrataeniatus, and H. trivittatus, the new species is distinguished by having a banded dorsal color pattern (instead of a striped pattern) and by the presence of subcaudal keels (absent in these species; Rossman in Peters and Orejas- Miranda, 1970; Cunha and Nascimento, 1978).
Helicops modestus and H. tapajonicus have a uniform dorsal coloration (dark olive in H. modestus and a uniformly dark green in H. tapajonicus; Frota, 2005) and lack subcaudal keels (instead of banded dorsal color pattern and presence of subcaudal keels in the new species). The new species can further be distinguished from H. tapajonicus by a higher number of dorsal scale rows (19/19/17 in both sexes of H. tapajonicus) and subcaudals (79 in a male and 67–76 in females of H. tapajonicus; Frota, 2005).
The new species shares a banded dorsal color pattern with H. angulatus and H. gomesi. The new species can be distinguished from H. angulatus by having a generally higher number of dorsal scale rows (19–21/19–20/17 in males and 19–21/19/17–19 in females of H. angulatus), of ventrals (111.2 +/- 3.4, range 105–123, n = 49 in males and 115.2 6 2.5 range 109–123, n = 62 in females of H. angulatus), and of subcaudals (87.1 +/- 5.1, range 75–96, n = 28 in males and 75.5 +/- 4.2, range 66–83, n = 38 in females of H. angulatus), and also by generally having fewer ventral blotches (20.5 +/- 2.1, range 15–25, n = 49 in males and 21 +/- 1.8, range 17–25, n = 63 in females of H. angulatus). Finally, Helicops apiaka can be distinguished from H. gomesi by having a higher number of dorsal scale rows (19 in both sexes in H. gomesi; Amaral, 1921).
Kawashita-Ribeiro, Ricardo Alexandre; Robson Waldemar Ávila, and Drausio Honorio Morais 2013. A New Snake of the Genus Helicops Wagler, 1830 (Dipsadidae, Xenodontinae) from Brazil. Herpetologica 69 (1): 80-90.