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Rhadinella donaji CAMPBELL, 2015

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Higher TaxaColubridae (Dipsadinae), Colubroidea, Caenophidia, Alethinophidia, Serpentes, Squamata (snakes) 
Subspecies 
Common NamesE: Donaji’s Slender Leaflitter Snake
S: Hojarasquera Delgada de Donaji 
SynonymRhadinella donaji CAMPBELL 2015 
DistributionMexico (Oaxaca)

Type locality: 13.6 km SW Villa Sola de Vega, 16.454873 N, -97.002701 W, 2195 m elevation [sometimes called San Miguel Sola de Vega], Oaxaca, Mexico  
Reproduction 
TypesHolotype: UTA R-4233, adult male (original field no. JAC 277), collected 8 June 1974 by Jonathan A. Campbell. The individual was found dead on the road during the early morning hours of an overcast day. 
DiagnosisDiagnosis: Small, gracile snake of the genus Rhadinella in which the head is only slightly distinct from neck. The head pattern alone is diagnostic from all other species of Rhadinella, consisting of a mostly pale dorsum with irregular head blotching followed by an immaculate pale collar (Fig. 1). Rhadinella donaji can easily be distinguished from most species of Rhadinella, such as R. hannsteini and R. kinkelini, which posses a distinct body pattern of longitudinal stripes. Rhadinella donaji can be most easily confused with R. schistosa, R. pilonaorum, and R. posadasi, all of which have a mostly dark dorsum, pale dashes on most dorsal scales, and often an indistinct dark vertebral line. Characteristics defining R. donaji include seven supralabials; third and fourth infralabials contacting posterior genials; 166 ventrals in single male; a mostly pale head with a relatively small amount of brown mottling; a pale collar that extends three scales posterior of the ultimate supralabial; an extremely faint dark vertebral stripe that involves only the vertebral scale row; no lateral stripe, but pale dashes that are less developed or absent on the third scale row; no dark pigment on lateral edges of ventrals; and only a very small amount of faint brown pigment on lateral edges of subcaudals, without darker pigment along subcaudal midline. Although the head proportions do not seem to vary significantly among species of Rhadinella, in R. donaji the frontal is slightly wider than long (2.6 w x 2.3 l), occupying 81.3% of the distance across the top of the head as measured from lateral edges of supraoculars, and the suproculars are relatively narrow (0.4 w x 1.3 l), whereas in R. pilonaorum, R. posadasi, and R. schistosa the frontal is longer than wide and the supraoculars are relatively broad.
Rhadinella donaji most closely resembles R. pilonaorum, but the latter taxon differs in having an auburn head cap heavily mottled in black (Fig. 2), followed by an pale orange collar; the fourth and fifth infralabials contact the posterior genials; there are eight supralabials (rarely seven), and males have 151–154 ventrals. The pale collar in R. pilonaorum extends no more than two scales posterior to the ultimate supralabial (vs. three); the posterior edges of supralabials are boldly edged with brown forming vertical barring; the parietals are heavily mottled with brown; the temporals are heavily edged with brown; dorsal color is dark, but a poorly defined vertebral stripe occupies the vertebral and adjacent half scale rows; an inconspicuous lateral stripe is present on adjacent halves of third and fourth scale rows; the lower edges of first scale row and lateral edges of ventrals distinctly edged with brown; and the lateral edges of ventrals are distinctly brown, with irregular pigment scattered along ventral midline of tail.
Rhadinella posadasi differs from the new species in having an almost uniformly dark head cap followed by a pale collar (Fig. 3); the fourth and fifth infralabials contact the posterior genials; 136–141 ventrals are present in males; a pale collar extending two scale rows posterior to ultimate supralabial; dorsal head plates, except posterior portion of parietals, including temporals mostly dark brown with small pale flecking; anterior supralabials to behind eye are mostly pale with no vertical barring, upper portion of these scales dark; posterior one and half to two supralabials dark; no trace of a lateral stripe; the lateral edges of ventrals and subcaudals with conspicuous brown pigment; and midventral surface of tail with almost continuous brown pigment along adjacent subcaudal sutures.
Rhadinella shistosa differs from the new species in having a dark head cap followed by a U-shaped collar that is often broken along the middorsal line; there 1+1 temporals (vs. 1+2); the tail is relatively short, accounting for only about 20% of total length; fourth and fifth infralabials contacting posterior genial; eight supralabials; 145–147 ventrals in males; supralabials mostly dark brown, but have a pale central spots or line; lateral edges of the ventrals and subcaudals are brown; and 16–17 maxillary teeth.
 
CommentHabitat: The type-locality is a heavily karstic region with many sharp rock ridges and pinnacles forming a honeycombed landscape that makes field work difficult. Pine-oak forest covers the landscape and in some areas a moderate accumulation of leaf litter may be found in rock crevices. 
EtymologyThis species is offered to the Princess Donají [pronounced softly in Zapotec as Donashi], who according to Zapotec legend was the beautiful granddaughter of King Cosijoeza, the last great king of the Zapotec civilization. She was taken hostage and subsequently decapitated by factions warring with the Zapotecs. Her head was lost, only to be discovered miraculously much later still in a fresh state by a shepherd digging up a flower. Her visage is represented on the coat of arms of the city of Oaxaca de Juárez. 
References
  • Ariano-Sánchez, D. y J. Campbell. 2018. A new species of Rhadinella (Serpentes: Dipsadidae) from the dry forest of Motagua Valley, Guatemala. Zootaxa 4442 (2): 338-344 - get paper here
  • CAMPBELL, JONATHAN A. 2015. A new species of Rhadinella (Serpentes: Colubridae) from the Pacific versant of Oaxaca, Mexico. Zootaxa 3918 (3): 397–405 - get paper here
  • CAMPILLO, GUSTAVO; LUIS FERNANDO DÁVILA-GALAVÍZ, OSCAR FLORES-VILLELA, JONATHAN A. CAMPBELL 2016. A new species of Rhadinella (Serpentes: Colubridae) from the Sierra Madre del Sur of Guerrero, Mexico Zootaxa 4103 (2): 165-173 - get paper here
  • Heimes, P. 2016. Snakes of Mexico. Chimaira, Frankfurt, 572 pp
  • Mata-Silva, Vicente, Jerry D. Johnson, Larry David Wilson and Elí García-Padilla. 2015. The herpetofauna of Oaxaca, Mexico: composition, physiographic distribution, and conservation status. Mesoamerican Herpetology 2 (1): 6–62 - get paper here
 
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