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Toxicocalamus nigrescens KRAUS, 2017

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Higher TaxaElapidae (Hydrophiinae), Colubroidea, Caenophidia, Alethinophidia, Serpentes, Squamata (snakes)
Common Names 
SynonymToxicocalamus nigrescens KRAUS 2017 
DistributionPapua New Guinea (Milne Bay Province)

Type locality: S slope Oya Waka, 9.4562°S, 150.5596°E (WGS84), 980 m elevation, Fergusson Island, Milne Bay Province, Papua New Guinea  
TypesHolotype: BPBM 16545 (field tag FK 6388), collected by P. Robert on 10 September 2002. Paratype: BPBM 16544. Papua New Guinea: Milne Bay Province: Fergusson Island: Basima, 9.4683°S, 150.8315°E, 0–10 m elevation. 
DiagnosisDescription: A moderately sized species of Toxicocalamus having 15-15-15 scale rows, 182–193 ventrals, 35–42 paired subcaudals, preocular unfused with prefrontal, separated from internasal by prefrontal, in contact with nasal; prefrontal in contact with nasal; frontal unfused with supraoculars; internasals unfused; 1 postocular; 1–2 anterior temporals, 2 posterior temporals, unfused with supralabials; 6 supralabials, second in contact with nasal, excluding contact between third supralabial and nasal; divided anal plate; relatively long snout (adult EN/IN = 1.8); uniformly dark gray-brown to charcoal-gray dorsum; and ventrum changing ontogenetically from uniformly pale gray to gray with dark-gray bands across each ventral.
The new species differs from Toxicocalamus holopelturus in having divided (vs. entire) subcaudals; from Toxicocalamus buergersi, T. longissimus, T. mintoni, Toxicocalamus misimae, Toxicocalamus preussi, and Toxicocalamus stanleyanus in having the preocular separate from (vs. fused to) the prefrontal; from T. pachysomus by its slender habitus (vs. robust in T. pachysomus) and in having the internasal and prefrontal not in contact but separated by contact of the nasal with the prefrontal (vs. internasal and prefrontal in contact in T. pachysomus); and from Toxicocalamus ernstmayri, Toxicocalamus grandis, and Toxicocalamus spilolepidotus in its uniformly dark-gray dorsal color (vs. yellow-brown spotted with dark brown in T. ernstmayri, dark brown with whitish blotches in T. grandis, black with each scale containing a pale-yellow spot in T. spilolepidotus).
Toxicocalamus nigrescens is most similar to T. loriae but differs from that species in having adult size larger (adult SVL = 635 mm and 69.5 g vs. 348–446 mm, average 399 mm; and 11.5–32.7 g, average 22.9 g, in T. loriae); relatively longer snout (adult EN/ IN = 1.0–1.1 in T. loriae); dorsum dark charcoal gray (vs. paler gray in T. loriae, Fig. 1A vs. Fig. 1B); ventrum banded with dark gray (vs. uniformly bright lemon yellow in adult T. loriae); subcaudals uniformly charcoal gray (vs. lemon yellow margined in gray in T. loriae); and supralabials mostly gray suffused over pale yellow-white (vs. lower half or two-thirds of supralabials bright lemon yellow in T. loriae, Fig. 1A vs. Fig. 1B in Kraus 2017). 
CommentHabitat: primary foothill rain forest with a moderately tall canopy reaching ~30 m and a fairly dense understory. The area had sparse moss development on the ground.

Morphologically, T. nigrescens is most easily distinguished from T. loriae by size and color-pattern characteristics, but head shape also appears different in life, and this may be quantified by focusing on two features: T. nigrescens has a relatively longer snout and relatively smaller eye than does T. loriae (Fig. 4 in Kraus 2017). This gives the head of T. nigrescens a distinctly different appearance than that of T. loriae (Fig. 1A vs. 1B). I noted the difference in snout shape in the diagnosis for T. nigrescens, because adult ratios were nonoverlapping for that feature and easily summarized diagnostically. On the other hand, differences in both snout-shape and eye-size characters between the species are most evident when viewed ontogenetically, with the two species having diverging trajectories (Fig. 4). Snout shape is the more divergent of the two, but T. nigrescens also has a relatively smaller eye at any given size than does T. loriae (Fig. 4B), although this difference is most easily seen in a bivariate plot rather than expressed as a simple ratio. 
EtymologyThe name is a Latin nominative single-ending adjective meaning both ‘‘blackish’’ and ‘‘blackening,’’ the former describing the feature that most immediately distinguishes it from the related T. loriae and the latter reflecting its ontogenetic change in color. 
  • Kraus, Fred 2017. Two New Species of Toxicocalamus (Squamata: Elapidae) from Papua New Guinea. Journal of Herpetology 51 (4): 574-581 - get paper here
  • O’Shea, Mark; Allen Allison, Hinrich Kaiser 2018. The taxonomic history of the enigmatic Papuan snake genus Toxicocalamus (Elapidae: Hydrophiinae), with the description of a new species from the Managalas Plateau of Oro Province, Papua New Guinea, and a revised dichotomous key. Amphibia-Reptilia 39 (4): 403-433 - get paper here
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