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Stegonotus aplini O’SHEA & RICHARDS, 2021

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Higher TaxaColubridae, Colubrinae, Colubroidea, Caenophidia, Alethinophidia, Serpentes, Squamata (snakes)
Common Names 
SynonymStegonotus aplini O’SHEA & RICHARDS 2021 
DistributionPapua New Guinea (Gulf Province)

Type locality: ca. 12 km NW of Orloli, Purari River basin, Gulf Province, PNG (7.3126°S, 145.1378°E, elevation ca. 20 m  
TypesHolotype. SAMA R71442 (field number SJR 15138), an adult male, collected by Ken Aplin on 22 June 2016.
Paratypes. PNGNM R25322 (field number SJR 15115), an adult male from ca. 6 km N of Orloli, Purari River basin, Gulf Province, PNG (7.3510°S, 145.1900°E, elevation ca. 30 m), collected by Ken Aplin on 11 February 2016; SAMA R71443 (field number SJR 15330), an adult male from ca. 1.6 km NW Muro Mission, Purari River basin, Gulf Province, PNG (7.7890°S, 145.2660°E, elevation ca. 5 m), collected by S. Richards and E. Nagombi on 12 July 2016; AMS R.13302, an adult male from the Kereru Range on the Abede River, Gulf Province, Papua New Guinea (ca. 7.0280°S, 144.4226°E, elevation uncertain) by geologist J. P. de Verteuil, probably in 1947 (collection date unavailable but catalogue entry dated 6 January 1948). 
DiagnosisDiagnosis. A species of Stegonotus that can be diagnosed from all congeners by the following combination of characters: dorsum of body immaculate snow-white anteriorly, with dark speckling that manifests as occasional brown-tipped scales by midbody and increases in frequency and density posteriorly; tail entirely dark brown with light pigment confined to lowest dorsal scale rows; venter and subcaudal scales off-white; head dorsally dark brown, contrasting with white anterior of the body, brown pigment extending posteriorly for 6–20 scales; dorsal scales rows 17-19-15 (75%) or 19-19-15 (25%), ventral scales 229–239, subcaudal scales 83–95, all divided; SL usually nine (75%), occasionally eight (25%), with SL4–SL5 contacting the orbit; and IL nine (75%), or eight (25%) with IL1–IL4 or IL1–IL5 contacting the anterior genials.

Colouration in life. The holotype and two paratypes were dorsally snow-white on the anterior and midbody regions, with infusions of black or very dark brown spots increasing in frequency from the midbody to posterior body. The dark pigment appears first on the posterior margins of the dorsal scales, gradually extending into the centres of each scale until by the tail the dorsum is primarily dark above, albeit still with large areas of white laterally. The venter is also immaculate white, with no dark pigmentation even posteriorly. The head is mid-brown dorsally, fading to light brown on the side of the head and on the neck. Although the colour in life of AMS R.13302 is unknown, its similarity in preservative to the remainder of the type series suggests a similar colouration in life.

Comparison with other species. Stegonotus aplini is a striking snake that can be immediately distinguished from all congeners with the exception of S. iridis by its colouration: at least the anterior third of the dorsal surfaces is snowy-white. All other congeners are unicolour grey, brown, or even black (S. borneensis Inger, 1967), or have white, yellow, pink or orange-red upward-pointing triangles anteriorly with a distinctly pale head laterally (S. batjanensis), or a reticulated pattern across the dorsum (S. reticulatus). Our new taxon most closely resembles S. iridis from the Raja Ampat Archipelago (Fig. 4), but the two species can be distinguished by the following characters (characters of S. aplini in parentheses): 17-19-15, 71%, or 17-17-15, 29%, dorsal scale rows (17-19-15 rows, 75%, or 19-19-15 rows, 25%); ventrals 198–211 (229–239); subcaudals 78–88 (83–95); SCR 0.28–0.31 (0.26–0.29); supralabials usually eight (86%), occasionally nine (14%) (usually nine, 75%, occasionally eight, 25%); infrabials ten, with IL1–IL5 contacting the anterior genials (usually nine, 75%, or eight, 25%, with IL1–IL4 or IL1–IL5 contacting anterior genials). The temporal scale arrangement of S. aplini (Figs. 3A–H) also differs from that of S. iridis (Figs. 3I–J). Both species exhibit elongate upper anterior and posterior temporals and whilst both species may occasionally exhibit fragmentation of these scales to form three upper temporals, fusion of these scales into a single elongate upper temporal, extending the entire length of the parietals, has only been observed in two of the S. aplini paratypes (PNGNM R25322; SAMA R71443). The lower anterior temporal in S. iridis is elongate, resulting in only two lower temporals contacting the upper anterior temporal, while three, occasionally four, squarish lower temporals contact the upper anterior temporal in S. aplini. Stegonotus iridis also appears to be a smaller species, with males not known to exceed 845 mm SVL (three of the four known males of S. aplini exceed 1000 mm SVL). A list of the major features of scalation that distinguish these two species is presented in Table 1, and a dichotomous key to the fourteen species of Stegonotus currently recognised on New Guinea and two additional species from adjacent areas that may occur in southern New Guinea, is provided below. 
EtymologyThe species epithet is a patronym to honour Dr. Ken Aplin (1958–2019), in recognition of his immense contributions to New Guinean herpetology, and in gratitude for his friendship and selfless collaboration with the junior author over many years. Ken’s many experiences in Melanesia have added significantly to our knowledge of the region’s vertebrate fauna, both living and fossil, and his recent passing has created a void that will be hard to fill. 
  • O’SHEA, M. & RICHARDS, S. J. 2021. A striking new species of Papuan groundsnake (Stegonotus: Colubridae) from southern Papua New Guinea, with a dichotomous key to the genus in New Guinea. Zootaxa, 4926(1): 26-42
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