Rhadinaea nuchalis, Garcia-Vazquez, Uri Omar, Pavon-Vazquez, Carlos J., Blancas-Hernandez, Jean Cristian, Blancas-Calva, Epifanio & Centenero-Alcala, Eric, 2018

Garcia-Vazquez, Uri Omar, Pavon-Vazquez, Carlos J., Blancas-Hernandez, Jean Cristian, Blancas-Calva, Epifanio & Centenero-Alcala, Eric, 2018, A new rare species of the Rhadinaeadecorata group from the Sierra Madre del Sur of Guerrero, Mexico (Squamata, Colubridae), ZooKeys 780, pp. 137-154 : 137

Rhadinaea nuchalis sp. n. Figs 1, 2, 3, 4, 5

Type material.

Holotype. MZFC-HE 22161, (original field number JCBH 015) an adult male, from 0.36 km SE of El Molote, municipality of Atoyac de Álvarez, Guerrero, México (17.4167°N; 100.1672°W), ca. 1720 m elevation, collected by J.C. Blancas-Hernández on July 19, 2006. Paratype. MZFC-HE 34958, (original field number CIG 1078) an adult male, from El Molote, municipality of Atoyac de Álvarez, Guerrero, México (17.4376°N; 100.1891°W), ca. 1680 m elevation, collected by Christoph I. Grünwald, Héctor Franz-Chávez, and Karen I. Morales-Flores on September 11, 2016.

Diagnosis.

A colubrid snake of the Rhadinaea decorata group (sensu Myers 1974) that may be distinguished from all other members of the genus Rhadinaea by the following combination of character states: eight supralabials; 149-151 ventrals in males; 63-77 subcaudals in males; presence of two large pale nuchal blotches, forming an incomplete collar that occupies two scales laterally and bissected along the dorsal midline; postocular pale marking consisting of a well-defined and narrow line beginning anteriorly behind the upper posterior margin of the eye and extending posteriorly nearly horizontally until connecting with the nuchal blotches; and ground color of the flanks extending to the lateral portion of the ventrals.

Comparison.

Rhadinaea nuchalis sp. n. may be distinguished from all other members of the genus Rhadinaea (except R. cuneata and some individuals of R. hesperia and R. omiltemana Günther, 1894) by the presence of two large pale nuchal blotches forming an incomplete collar that occupies two scales laterally and is bissected along the dorsal midline (pale nuchal marking one-scale long in R. laureata ( Günther, 1868) and R. marcellae , absent in the other species). Rhadinaea nuchalis can be further distinguished from the members of the R. flavilata group by the presence of eight supralabials (usually seven in the R. flavilata group). Additionally, it differs from R. calligaster (Cope, 1875), R. forbesi , R. hesperia , R. marcellae , R. macdougalli , and R. montana by the presence of a well-defined, pale postocular line beginning anteriorly behind the upper posterior margin of the eye and extending nearly horizontally posteriorly until connecting with the nuchal blotches (pale postocular line oblique in R. calligaster [if present], R. forbesi , R. macdougalli , and R. marcellae ; not connected with the pale post-cephalic markings in the other species [except for one side in one specimen of R. montana ]).

Furthermore, Rhadinaea nuchalis can be distinguished from members of the R. vermiculaticeps group by having more ventrals in males (149-151 vs. 117-124 ventrals in males of the R. vermiculaticeps group). Rhadinaea nuchalis differs from R. cuneata by having less subcaudals in males (63-77 vs. 106-115) and by having a narrow postocular pale marking in the form of a nearly horizontal line (postocular pale marking wedge-shaped in R. cuneata ). Specifically, R. nuchalis differs from other congeners that inhabit Guerrero except R. myersi by having fewer subcaudals in males (63-77 vs. 110-137 in R. hesperia ; 85-90 in R. omiltemana ; 91-121 in R. taeniata Peters, 1863). Additionally, it differs from R. myersi , R. omiltemana , and R. taeniata by having the dark ground color of the flanks extending to the lateral portion of the ventrals (dark ground color of the flanks not reaching ventrals in R. omiltemana , occasionally and faintly so in R. myersi and R. taeniata ).

Description of holotype

(Figs 1, 2). Male; adult; head length = 12.2 mm, snout-vent length (SVL) = 275 mm, tail length = 104 mm. Head distinct from neck; snout long, contained 2.5 times in head length, rounded from above, projecting anteriorly beyond lower jaw; rostral broader than high, portion visible from above 0.6 times as long as its distance from frontal, 0.5 times as long as internasal common suture, upper edge slightly above level of upper margin of nostrils; internasals broader than long (width / length = 1.5), rounded laterally, contacting anterior and posterior nasals laterally, length and common suture ca. 0.8 and 0.4 times as long as prefrontal common suture, respectively; prefrontal contacting postnasal and loreal laterally, length ca. 0.3 times length of snout, common suture ca. 0.5 times frontal length; frontal longer than broad (width / length = 3.6/2.3), angulate posteriorly; supraocular large, contacting prefrontal, frontal, parietal, and upper postocular broadly, length ca. 1.3 times length of horizontal diameter of eye, 1.3/1.3 times as long as loreal, ventral margin projecting anteriorly and posteriorly beyond margins of orbit; parietals 1.6 times longer than broad, length approximately 0.4 times head length, common suture as long as frontal; nasal divided; prenasal 1.3/1 times as long as postnasal; prenasal and postnasal combined length ca. 2.3 times loreal length; loreal as high as long, contained 1.1 times in snout length, 0.4 times as long as horizontal diameter of eye, dorsal margin nearly straight; preocular single, 1.8 times higher than long; subpreocular present, tiny, separating preocular and fourth supralabial; postoculars two; upper postocular 1.4 times higher than long, 2.3 times longer than lower postocular; lower postocular 2.25 times longer than high; eye large, contained 4.1 times in snout length, vertical diameter 2.0 times distance from lip; supralabials 8/8, first and second contacting postnasal, second and third contacting loreal, fourth and fifth entering orbit, seventh largest, contacting anterior temporal, eight contacting lower posterior temporal; temporals 1 + 2; anterior temporal separating sixth and seventh supralabials from parietal; upper posterior temporals separated posteriorly by five nuchals; lower posterior temporal contacting anterior temporal and seventh supralabial anteriorly, eight supralabial ventrally. Mental 1.5 times broader than long, rounded anteriorly, separated from chinshields by first infralabials; infralabials 10/10, first to third contacting anterior chinshields, fourth to sixth separated from chinshields by interstitial skin, seventh to tenth separated by other scales; anterior chinshields 3.3 times longer than broad, as long as posterior chinshields; posterior chinshields separated from each other by two midgular scales.

Transverse dorsal scale rows 17-17-17, smooth; apical pits absent; ventrals 151; cloacal scute divided; paired subcaudals 63.

Color (in life; Figs 3-4). Dorsum of head ochre, extending to rostral anteriorly, to third dorsal scale posterior to parietals posteriorly along the dorsal midline, narrowing occupying one dorsal scale laterally; extending to upper half of nasal, lateral portion of prefrontal, upper third of preocular, lateral edge of supraocular, uppermost portion of upper postocular, lateral portion of parietal, and ventral portion of upper secondary temporal and dorsal scale posterior to it ventrolaterally; irregular dark markings present, except on ventral border anteriorl to orbit (creating the appearance of a faint preocular line). Postocular pale marking consisting of a nearly horizontal, black-bordered, cream line; beginning anteriorly on rear upper fourth of orbit; passing along upper portion of upper postocular, lateral portion of parietal, and upper portion of primary temporal, connecting with nuchal blotches posteriorly. Lateral stripe dark brown, black-bordered; ventrally bordering faint preocular line and postocular pale marking; extending anteriorly to posterior nasal, eighth supralabial posteriorly; occupying upper border of supralabials 1-6, upper half of supralabial 7, and entire surface of supralabial 8 except for anteroventral corner. Ground coloration below dark lateral stripe white, interspaces between each scale bright pink; supralabials 1-7, mental, infralabials, and anterior chinshields with irregular dark markings.

Nuchal blotches brownish orange; separated dorsally by median dark line; one dorsal scale long dorsally, widening laterally to two dorsal scales; nearly immaculate dorsally, with abundant dark speckling at level of supralabials; connected to pale ventral coloration. First and second transverse dorsal scale rows posterior to nuchal blotches reddish brown, slightly darker than rest of body.

Coloration of rest of body and tail: median dark line dark brown, with darker spots on tip of each dorsal scale in vertebral row; extending to third mid-dorsal scale posterior to parietals anteriorly, to tip of tail posteriorly; narrower anteriorly and posteriorly (confined to vertebral dorsal scale row near head and to medial edges of innermost dorsal scale rows in tail), wider at midbody (occupying vertebral dorsal scale row entirely and dorsal edges of adjacent dorsal scale rows). Dorsolateral stripe ochre; failing to contact nuchal blotches anteriorly by two scales, extending to tip of tail posteriorly; extending between upper portion of fifth and lower portion of eighth longitudinal dorsal scale rows at level of mid-body, between upper portion of second and lower portion of third longitudinal dorsal scale rows at level of mid-tail. Scales on fifth longitudinal dorsal scale row at level of mid-body and second at level of mid-tail exhibiting prominent orange spots. Lateral dark line bordering dorsolateral stripe ventrally; contacting nuchal blotches anteriorly, extending to tip of tail posteriorly; occupying three longitudinal dorsal scale rows just posteriorly to head, upper portion of fourth and lower edge of fifth longitudinal dorsal scale rows at level of mid-body, upper edge of first and lower edge of second longitudinal dorsal scale rows at level of tail. Flanks dark ochre, slightly darker than dorsolateral stripes, presenting abundant dark speckling. Ground color of flanks extending ventrally onto lateral portions of ventrals and subcaudals. Lateral portion of ventrals with black spots posteriorly at level of ventral edge of color of flanks. Conspicuous dark line passing along lateral edge of subcaudals. Remaining surface of ventrals and subcaudals white, suffused lightly with bright pink from head to level of mid-body, with sparse tiny dark dots.

Hemipenes (Figure 5). Hemipenes unilobed, unicapitate, length ≈ 5 mm. Sulcus spermaticus centripetal basally, centrolineal distally; bifurcating at level of distal end of basal third of capitulum, terminating distally at level of basal end of distal third of capitulum; sulcus spermaticus walls smooth, well-defined; intrasulcar region nude. Capitulum calyculate, longer on sulcate side (≈ 2.5 mm, vs. ≈ 1.2 mm on asulcate side); calyces papillate in most of capitulum, spinulate near base of capitulum. Hemipenial body covered in spines distally; enlarged spines 30, slightly curved, larger and more abundant on lateral surfaces of hemipenial body and asulcate side than on sulcate side; area of hemipenial body below spinose section covered in small spinules; spinules surrounding sulcus spermaticus walls, covering larger area on sulcate and asulcate sides than on lateral surfaces of hemipenial body, separated from enlarged spines by triangular nude patch on asulcate side. Basal-most portion of hemipenial body nude.

Variation.

The paratype differs from the holotype by having the upper posterior temporal divided into two small scales on the right side, 10/9 infralabials, the posterior chinshields separated from first ventral by two rows of small scales, 149 ventrals, and 77 subcaudals. No remarkable differences in color pattern are present in the paratype with respect to the holotype.

Etymology.

The specific name nuchalis comes from the Latin nucha, meaning nape. It makes reference to the large nuchal blotches present in the new species.

Distribution and ecology.

Rhadinaea nuchalis sp. n. is known only at intermediate elevations from the vicinity of El Molote in the western portion of the Sierra Madre del Sur of Guerrero. The species appears to be allopatric with the other species of the R. decorata group. The closest Rhadinaea record to R. nuchalis is that of R. omiltemana from El Tambor, Coyuca de Benítez, Guerrero, approximately 8 km E in straight line from the type locality of R. nuchalis ( Palacios-Aguilar et al. 2016). The second closest record is that of R. taeniata from 1.5 mi N San Vicente de Jesus, Guerrero, about 18 km SSW in straight line from the type locality of R. nuchalis ( Myers 1974). Other close records are those of R. omiltemana from Omiltemi and Asoleadero, R. hesperia from Acahuizotla and Chilpancingo, and R. taeniata from Chilpancingo, all in Guerrero (Fig. 6). All the three are about 72 km, straight line, from the type locality of R. nuchalis The closest records of species in the R. decorata group, excluding those of R. hesperia , to the type locality of R. nuchalis are those of R. myersi from Malinaltepec, Guerrero, and southwestern Oaxaca ( García-Vázquez et al. 2006); and those of R. macdougalli and R. bogertorum from northern Oaxaca ( Myers 1974, Ramírez-Bautista et al. 1998).

The region of El Molote is characterized by rugged topography and the presence of numerous permanent streams that flow into the Atoyac and Coyuca rivers, whose basins belong to the Costa Grande hydrologic region ( Lozada et al. 2003). Additional descriptions of the climate and other ecological aspects of El Molote can be found in Meza and López (1997) and Pavón-Vázquez et al. (2011). Coffee plantations have replaced most of the original cloud forest. The forest is dense and tall in undisturbed places, with the canopy reaching 25-30 m in height (Fig. 7). Pinus ayacahuite , P. strobus var. chiapensis , and Ulmus mexicana are emergent species, and Alfaroa costaricensis , Sloanea sp., Quercus salicifolia , Cojoba arborea , Magnolia schiedeana , and Zanthoxylum melanostictum are dominant species ( Lozada et al. 2003).

Identification key

An identification key to the species of Rhadinaea was included in Myers’s (1974) revision of the genus. Examination of the known specimens of R. nuchalis would lead to couplet number 40 in Myers’s (1974) key for North American species. Modifying number 40 as follows would allow the identification of R. nuchalis :

Former number 40, a bracket including R. bogertorum and R. myersi , would become number 41.