Oxyrhopus melanogenys (Tschudi)
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publication ID |
https://doi.org/ 10.1590/S0031-10492009003600001 |
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persistent identifier |
https://treatment.plazi.org/id/0608A176-FF9C-1745-3624-FEDFFB1B5568 |
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treatment provided by |
Felipe |
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scientific name |
Oxyrhopus melanogenys (Tschudi) |
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Oxyrhopus melanogenys (Tschudi) View in CoL
Taxonomic history
Oxyrhopus melanogenys was originally described from the southwestern Amazon region. This species has been confused with the similar-appearing O. trigeminus . Oxyrhopus melanogenys can be distinguished from O. trigeminus by its entirely black head (snout white with black spots in O. trigeminus ), by the outer black bands of the triads narrower than the central black band (all three black bands equal) and by the white bands of triads narrower than the black bands (equal to the black bands)( Table 2).
Historical reports of O. trigeminus in Guyana are based on two specimens ( BMNH 1990.19 and 1990.20) from “ Demerara ” (= Georgetown, Guyana) donated by Captain E. Sabine between 1818 and 1824. However, the “ Demerara ” locality must be regarded as highly dubious, because numerous specimens donated by Sabine to BMNH, purportedly from Demerara, are really from other localities ( Underwood, 1993; C. McCarthy, pers. comm.). Donnelly et al. (2005) reported a specimen of Oxyrhopus trigeminus from Iwokrama in central Guyana, but the specimen was re-identified as O. melanogenys by RDM and AL. Lancini (1979) and Kornacker (1999) mentioned O. trigeminus from Venezuela (photograph in Kornacker, 1999), but Zaher & Caramaschi (1992) demonstrated that these are really O. melanogenys . All other known specimens of O. trigeminus are from south of the Amazon River ( Zaher & Caramaschi, 1992).
Consequently, we exclude O. trigeminus from the fauna of Guyana and the Guiana Shield. Any reports of O. trigeminus from the region are actually of O. melanogenys . We include O. trigeminus in Table 2 only to point out differences between it and O. melanogenys .
A taxon identified as Oxyrhopus aff. melanogenys has been reported from the Guiana Shield ( Zaher & Caramaschi, 1992; Starace, 1998). There are no significant morphological differences between Oxyrhopus melanogenys and O. aff. melanogenys . The two taxa differ solely in the degree of fusion of anterior triads, a character that we feel insufficient to distinguish between species. We therefore consider O. aff. melanogenys to be O. melanogenys .
Material examined – Six males, five females and one juvenile (Appendix).
Morphology
Maximum total length in our sample is 810 mm; maximum reported length is 930 mm ( Starace, 1998). Lower labials 10; six in contact with shields. In AMNH 152279 and 152280 the uppermost posterior temporal on the left side is fused with the adjacent posterior scale to produce an elongate scale, equal in length to the parietal; temporals on the right side are normal. IRSNB 17940 has a similar scale fusion on both sides of the head. Measurements of adults are in Table 1. The single juvenile measures 183 mm SVL, tail 49 mm, with 190 ventrals and 82 subcaudal pairs. The tail of the juvenile is 21% of its total length, vs. 23-27% in adult males and 20-22% in adult females.
Colour and Pattern
Oxyrhopus melanogenys has a triad colour pattern (a triad is a repeating series of bands, black-whiteblack-white-black, separated by red or orange interspaces) ( Figs. 1D View FIGURE 1 , 3 View FIGURE 3 ). In all but one O. melanogenys examined (n = 10) the body bands anterior to the triads are symmetrical (nuchal red/orange, black, white, black, red/orange, then triads). In CSBD HR700 some of the body bands anterior to the triads are asymmetrical. In all other specimens, symmetry breaks down in the first triad; the anterior white band of this triad is symmetrical, but the posterior is not. In many individuals all subsequent triads, anterior to the vent region, are asymmetrical. The vent is in the central black band of a triad; this is the first symmetrical triad in all but two snakes; in these two individuals ( AMNH 140898 About AMNH , MAD 1368 View Materials ) the triad anterior to the triad that straddles the vent is also symmetrical. In three specimens, AMNH 8094 About AMNH , AMNH 98211 About AMNH and MAD 1368 View Materials , triads become symmetrical just posterior to the midpoint between snout and vent, then become asymmetrical again, then once again symmetrical at the vent triad or the triad anterior to it. Triads anterior to vent 15.5-20.5; triads on the tail are difficult to count because tails become very dark, with triads indicated by only a few light flecks ( Fig. 3 View FIGURE 3 ). In IRSNB 17941 View Materials and CSBD HR700 , the anterior colour pattern consists of white body bands on a dark background, with triads detectable only posteriorly (2.5 anterior to vent in IRSNB 17941 View Materials , 4.5 in CSBD HR700 ), when red interspaces become visible laterally. In AMNH 8094 About AMNH , AMNH 98211 About AMNH , MAD 1368 View Materials and ROM 39439 About ROM , the nuchal band is complete and symmetrical, broader laterally than middorsally. In AMNH 140898 About AMNH , 152279 About AMNH and 152280 the nuchal band and the next interspace are present laterally but incomplete dorsally. In AMNH 98211 About AMNH , AMNH 152279 About AMNH , AMNH 152280 About AMNH and ROM 39439 About ROM , the interspaces between the anteriormost triads do not extend up to the middorsal line. In IRSNB 17912 View Materials and IRSNB 17941 View Materials the nuchal band is incomplete, only barely distinguishable laterally. In IRSNB 17912 View Materials the next interspace is present, but red bands are then absent until slightly posterior to the midpoint between snout and vent. In IRSNB 17941 View Materials the next red interspace is absent, red bands are absent except at the very end of the body where two red bands are barely distinguishable laterally. The width of the interspaces between triads is variable, even within the same individual; in some cases they are equal to the outer black triad bands and in others they are wider, equal to the central black bands. In most specimens, dark pigment is present on outer edges of ventrals anteriorly, extending further onto ventrals posteriorly, often extending across ventrals that are immediately anterior to vent. In AMNH 8094 About AMNH and AMNH 140898 About AMNH the dark bands touch only the outer edges of ventrals .
In general, larger, presumably older, individuals have less prominent markings than do smaller, younger specimens. Partial melanism was reported by Starace (1998), who noted that the nuchal band is always present in partially melanistic individuals; similar melanism was observed in central French Guiana by PJRK (unpublished data).
Because of its triad colour pattern, Oxyrhopus melanogenys is considered a coral snake mimic. A summary of this mimicry is in Campbell & Lamar (2004). Photographs are in Zaher & Caramaschi (1992), Starace (1998), Kornacker (1999 [as O. trigeminus ]), Campbell & Lamar (2004) and MacCulloch & Lathrop (2009).
Distribution in the Guiana Shield
Zaher & Caramaschi (1992) map the distribution of Oxyrhopus melanogenys . Additional locations in the Guiana Shield, other than Guyana, are in Starace (1998) and Gorzula & Señaris (1999). Oxyrhopus melanogenys is a forest dweller; habitat description is in Donnelly et al. (2005) and Kok & Kalamandeen (2008). Distribution in Guyana is mapped in Fig. 2 View FIGURE 2 .
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.