Literature used for the morphologic assessments Aguiar, L.F.S. de; Di-Bernardo, M. (2005): Reproduction of the water snake Helicops infrataeniatus (Colubridae) in southern Brazil. In Amphibia-Reptilia 26 (4), pp. 527–533. DOI: https://doi.org/10.1163/156853805774806205. Amaral, A.d. (1921): Contribution towards the knowledge of snakes in Brazil - A. Part I: Four new species of Brazilian snakes. In Memórias do Instituto Butantan 1, pp. 39–44. Amaral, A.d. (1937): Estudo sobre ophidios neotropicos. 34. Novas notas sobre a fauna da Colombia e descripcao de uma especie nova de Colubrideo aglypho. In Memórias do Instituto Butantan 11, pp. 232–240. Barrio-Amoros, C.; Brewer-Carias, C. (2008): Herpetological results of the 2002 expedition to Sarisariñama, a tepui in Venezuelan Guayana, with the description of five new species. In Zootaxa 1942 (1), pp. 1–68. Boos, H. E. A. (2001): The snakes of Trinidad and Tobago. College Station: Texas A&M University Press. Boulenger, G. A. (1893): Catalogue of snakes in the British Museum. London: Order of the Trustees of the British Museum. Cope, E.D. (1868): Sixth contribution to the herpetology of tropical America. In Proceedings of the Academy of Natural Sciences of Philadelphia, pp. 305–313. Cope, E.D. (1877): Tenth contribution to the herpetology of tropical America. In Proceedings of the American Philosophical Society 17 (100), pp. 85–98. Cope, E.D. (1885): Twelfth contribution to the herpetology of tropical America. In Proceedings of the American Philosophical Society 22 (118), pp. 167–194. Cope, E.D. (1895): The classification of the Ophidia. In Transactions of the American Philosophical Society 18 (2), pp. 186–219. Costa, H.C.; Santana, D.J.; Leal, F.; Koroiva, R.; Garcia, P.C.A. (2016): A new species of Helicops (Serpentes: Dipsadidae: Hydropsini) from southeastern Brazil. In Herpetologica 72 (2), pp. 157–166. DOI: https://doi.org/10.1655/HERPETOLOGICA-D-15-00059 Cunha, O.R.d.; Nascimento, F.P.d. (1993): Ofídios da Amazônia. As cobras da região leste de Pará. In Boletim do Museu Paraense Emilio Goeldi, série Zoologia 9 (1). da Frota, J.G. (2005): New species of Helicops Wagler, 1830 (Serpentes, Colubridae) from Tapajós river, Amazon region, Brazil. In Phyllomedusa: Journal of Herpetology 4 (1), pp. 61–67. Deiques, C.H.; Cechin, S.Z. (1991): O status de Helicops carinicaudus (Wied, 1825)(Serpentes: Colubridae). In Acta Biológica Leopoldensia 12, pp. 313–326. Dixon, J. R.; Soini, P. (1986): The reptiles of the Upper Amazon Basin, Iquitos region, Peru. Rev. ed. Milwaukee, WI: Milwaukee Public Museum. Emsley, M.G. (1977): Snakes, and Trinidad and Tobago. In Bulletin of the Maryland Herpetological Society 13, pp. 201–306. Ford, N.B.; Ford, D.F. (2002): Notes on the ecology of the South American water snake Helicops angulatus (Squamata: Colubridae) in Nariva Swamp, Trinidad. In Caribbean Journal of Science 38 (1-2), pp. 129–131. França, F.G.R.; Mesquita, D.O.; Nogueira, C.C.; Araújo, A.F.B. (2008): Phylogeny and Ecology Determine Morphological Structure in a Snake Assemblage in the Central Brazilian Cerrado. In Copeia 2008 (1), pp. 23–38. DOI: https://doi.org/10.1643/CH-05-034. Gray, J. E. (1849): Catalogue of the Specimens of Snakes in the Collection of the British Museum. London: Order of the Trustees of the British Museum. Griffin, L. E. (1916): A catalog of the Ophidia from South America at present (June, 1916) contained in the Carnegie Museum, with descriptions of some new species. Pittsburgh: Carnegie Institute (Publications of the Carnegie Museum, serial, 92). Günther, A.C.L.G. (1861): On the ophidian genus Helicops. In The Annals and magazine of natural history; zoology, botany, and geology 7, pp. 425–428.Hagmann, G. (1910): Die Reptilien der Insel Mexiana, Amazonenstrom. In Zoologische Jahrbücher, Abteilung für Systematik, Geographie und Biologie der Tiere 28 (5), pp. 473–504. Hoge, A.R. (1952a): Notas erpetológicas. 1a. contribuição ao conhecimento dos ofidios do Brasil Central. In Memórias do Instituto Butantan 24 (2), pp. 179–214. Hoge, A.R. (1952b): Notas erpetologicas. 2a. contribuicao ao conhecimento dos ofidios do Brasil central. In Memórias do Instituto Butantan 24 (2), pp. 215–224. Hoge, A.R.; Nina, A.C. (1969): Serpentes coletadas pelo Instituto nacional de Pesquisas da Amazônia. In Memórias do Instituto Butantan 30, pp. 71–96. Jan, G. (1865): Enumerazione sistematica degli ofidi appartenenti al gruppo Potamophilidae. In Archivo per la Zoologia, l’Anatomia e la Fisiologia 3, pp. 201–265. Kawashita-Ribeiro, R.A. (2019): Coloration of Helicops apiaka. E-Mail to Yannis Schöneberg, 12.09.2019. Kawashita-Ribeiro, R.A.; Ávila, R.W.; Morais, D.H. (2013): A new snake of the genus Helicops Wagler, 1830 (Dipsadidae, Xenodontinae) from Brazil. In Herpetologica 69 (1), pp. 80–90. DOI: https://doi.org/10.1655/HERPETOLOGICA-D-12-00013. Lancini, A. R.; Kornacker, P. M. (1989): Die Schlangen von Venezuela. Dt., übers., ergänzte sowie völlig neu überarb. u. gestaltete Fassung. Caracas: Armitano. Maia, D.C.; Silva, A.G.D.; Travaglia-Cardoso, S.R. (2015): Helicops modestus (Ophidia: Dipsadidae): Reproduction. In Acta zoológica mexicana 31 (2), pp. 333–334. Marques, O. A. V.; Eterovic, A.; Sazima, I. (2001): Serpentes da Mata Atlântica: guia ilustrado para a Serra do Mar. Ribeirão Preto: Holos. Marques, O. A. V.; Eterovic, A.; Strüssmann, C.; Sazima, I. (2005): Serpentes do pantanal. Guia ilustrado. Ribeirão Preto: Holos. Marques, O.A.V.; Sazima, I. (2004): Historia natural dos repteis da Estacao Ecologica Jureia-Itatins. In Otávio Augusto Vuolo Marques (Ed.): Estação Ecológica Juréia-Itatins. Ambiente físico, flora e fauna. Ribeirão Preto, SP: Holos Editora, pp. 257–277. Martins, M.; Oliveira, M.E. (1998): Natural history of snakes in forests of the Manaus region, Central Amazonia, Brazil. In Herpetological Natural History 6 (2), pp. 78–150. Mole, R.R. (1924): The Trinidad Snakes. In Proceedings of the Zoological Society of London 94 (1), pp. 235–278. DOI: https://doi.org/10.1111/j.1096-3642.1924.tb01500.x. Moraes-da-Silva, A.; Amaro, R.C.; Nunes, P.M.S.; Rodrigues, M.T.; Curcio, F.F. (2021): Long known, brand new, and possibly threatened: a new species of watersnake of the genus Helicops Wagler, 1828 (Serpentes; Xenodontinae) from the Tocantins-Araguaia River Basin, Brazil. In Zootaxa 4903 (2), pp. 217–241. DOI: https://doi.org/10.11646/zootaxa.4903.2.3. Moraes-da-Silva, A.; Amaro, R.C.; Nunes Sales, P.M.; Strüssmann, C.; Teixeira Junior, M.; Andrade, A., J.; Sudre, V.; Recoder, R. et al. (2019): Chance, luck and a fortunate finding: a new species of watersnake of the genus Helicops Wagler, 1828 (Serpentes: Xenodontinae), from the Brazilian Pantanal wetlands. In Zootaxa 4651 (3), pp. 445–470. DOI: https://doi.org/10.11646/zootaxa.4651.3.3. Murphy, J. C. (1997): Amphibians and reptiles of Trinidad and Tobago. Malabar: Krieger Publishing Company. Paolillo, A. (1986): Geographic distribution: Helicops hagmanni (mapanare de agua). In Herpetological Review 17 (2), p. 49. Pérez-Santos, C.; Moreno, A. G. (1991): Serpientes de Ecuador. Torino: Museo Regionale di Scienze Naturali (Monografie, 11). Peters, J. A.; Orejas-Miranda, B.; Donoso-Barros, R.; Vanzolini, P. E. (1986): Catalogue of the neotropical squamata. Rev. ed. Washington, D.C.: Smithsonian Institution Press. Roze, J.A. (1957): Notas sobre Hydrops lehmanni Dunn, 1944, y los géneros neotropicales: Pseudoeryx, Hydrops y Helicops (Colubridae). In Acta Biológica Venezuelica 2, pp. 17–26. Rossman, D.A. (1975): Redescription of the South American colubrid snake Helicops hagmanni Roux. In Herpetologica 31 (4), pp. 414–418. Rossman, D.A. (1976): Revision of the South American colubrid snakes of the Helicops pastazae complex. In Occasional Papers of the Museum of Zoology (50). Rossman, D.A. (2002a): Morphological variation in the endemic Colombian water snake, Helicops danieli Amaral, 1937 (Serpentes: Xenodontidae). In Revista de la Academia Colombiana de Ciencias 26 (101), pp. 589–594. Rossman, D.A. (2002b): Variation in the xenodontid water snake Helicops scalaris Jan, and the status of H. hogei Lancini. In Occasional Papers of the Museum of Natural Science 78, pp. 1–18. Rossman, D.A. (2010): Morphological variation in the striped water snake Helicops trivittatus (Gray, 1849)(Reptilia: Serpentes: Xenodontidae) of eastern Amazonia. In Boletim do Museu Paraense Emílio Goeldi Ciências Naturais 5 (3), pp. 271–278. Rossman, D.A.; Abe, A.S. (1979): Comments on the taxonomic status of Helicops yacu (Serpentes: Colubridae). In Proceedings of the Louisiana Academy of Sciences 42, pp. 7–9. Rossman, D.A.; Dixon, J.R. (1975): A new colubrid snake of the genus Helicops from Peru. In Herpetologica 31 (4), pp. 412–414. Roux, J. (1910): Eine neue Helicops-Art aus Brasilien. In Zoologisher Anzeiger 36, pp. 439–440. Roveri Scartozzoni, R.; Almeida-Santos, S.M. de (2006): Helicops leopardinus (Water snake): reproduction. In Herpetological bulletin (97), pp. 39–40. Santos-Jr, A.P.; Ribeiro, F.R. (2005): Dimorfismo sexual em uma prole da cobrad’água Helicops polylepis Gunther, 1861 (Serpentes: Colubridae) do oeste do estado do Pará, Brasil, com comentários sobre o período reprodutivo. In Comunicações do Museu de Ciências e Tecnologia da PUCRS, série Zoologia 18 (1), pp. 67–71. Schmidt, K. P.; Walker, W. F. (1943): Peruvian snakes from the University of Arequipa. Chicago: Field Museum of Natural History (Zoological Series). Shaw, G.; Griffith; Heath, C.; Stephens, J. F. (1802): General zoology, or Systematic natural history. London: Printed for G. Kearsley (v.3:pt.2 (1802)). Shreve, B. (1934): Notes on Ecuadorian snakes. In Occasional Papers of the Boston Society of Natural History 8, pp. 125–132. Silva Jr, N.J. (1993): The snakes from Samuel hydroelectric power plant and vicinity, Rondônia, Brazil. In Herpetological Natural History 1 (1), pp. 37–86. Strussmann, C.; Sazima, I. (1993): The snake assemblage of the Pantanal at Poconé, Western Brazil: Faunal composition and ecological summary. In Studies on Neotropical Fauna and Environment 28 (3), pp. 157–168. DOI: https://doi.org/10.1080/01650529309360900. Vanzolini, P. E.; Ramos-Costa, A. M. M.; Vitt, L. J. (1980): Répteis das caatingas: Academia Brasileira de Ciências. Werner, F. (1897): Ueber einige neue und seltene Reptilien und Frösche der zoologischen Sammlung des bayrischen Staates in München. In Sitzungsberichte der Bayerischen Akademie der Wissenschaften zu München, Mathematisch-Physikalische Klasse 27 (2), pp. 203–220. Whitworth, A.; Beirne, C. (2011): Reptiles of the Yachana Reserve. Exeter: Global Vision International. Wied-Neuwied, M.z. (1824): Verzeichnis der Amphibien welche in zweiten Bande der Naturgeschichte Brasiliens von Prinz Max von Neuwied werden beschreiben werden. In Isis von Oken 14, pp. 661–673. Williams, J.D.; Scrocchi, G.J. (1994): Ofidios de agua dulce de la República Argentina. In Raúl Adolfo Ringuelet (Ed.): Fauna de agua dulce de la República Argentina, vol. 42. Buenos Aires, pp. 1–55. Yuki, R.N. (1994): Regarding Helicops danieli Amaral, 1937, with a description of the hemipenis (Serpentes, Colubridae, Xenodontinae). In Boletim do Museu Paraense Emilio Goeldi, série Zoologia 10 (2), pp. 203–209. Yuki, R.N.; Lema, T. (2005): Análise comparativa entre as cobras d’água meridionais (Helicops carinicaudus (Wied, 1825) e Helicops infrataeniatus Jan, 1865), com a descrição do crânio e hemipênis (Serpentes: Colubridae: Xenodontinae). In Comunicações do Museu de Ciência e Tecnologia da PUCRS, Série Zoologia 18, pp. 85–128. Yuki, R.N.; Santos, R.d. (1996): Snakes from Marajó and Mexiana islands, Pará state, Brazil. In Boletim do Museu Paraense Emílio Goeldi 12 (1), pp. 41–53. Zaher, H. (1999): Hemipenial morphology of the South American xenodontine snakes : with a proposal for a monophyletic Xenodontinae and a reappraisal of colubroid hemipenes. In Bulletin of the American Museum of Natural History 240, pp. 1–168. Available online at http://digitallibrary.amnh.org/bitstream/2246/1646/1//v2/dspace/ingest/pdfSource/bul/B240a01.pdf.