Atractus echidna, Passos, Paulo, Mueses-Cisneros, Jonh Jairo, Lynch, John D. & Fernandes, Ronaldo, 2009

Passos, Paulo, Mueses-Cisneros, Jonh Jairo, Lynch, John D. & Fernandes, Ronaldo, 2009, Pacific lowland snakes of the genus Atractus (Serpentes: Dipsadidae), with description of three new species, Zootaxa 2293, pp. 1-34 : 8-10

Atractus echidna sp. nov.

Fig. 5

Holotype: Adult male, UV-C 7718, from estero San Antonio, Flor de la Briza, corregimiento Robles (01º42’N, 78º42’W, ca. 10 m), municipality of Tumaco, department of Nariño, Colombia.

Diagnosis: Atractus echidna is distinguished from all congeners by the combination of the following characters: (1) 15/15/15 smooth dorsals; (2) two postoculars; (3) long loreal; (4) temporals 1+2; (5) seven supralabials, third and fourth contacting orbit; (6) seven infralabials, first three contacting chinshields; (7) six maxillary teeth; (8) three gular scale rows; (9) three preventrals; (10) 127 ventrals in the single male; (11) 36 subcaudals; (12) dorsum light brown with irregular dark brown blotches decreasing in size posteriorly; (13) venter uniformly cream anteriorly and scattered with brown posteriorly; (14) small body size, male reaching 201 mm SVL; (15) tail long in male (23.4% of SVL).

Comparisons: Among all congeners, A. echidna and A. iridescens are the only species with fewer than 150 ventrals and more than 35 subcaudals in males, four or five prediastemal and two postdiastemal wellspaced teeth, and dorsum reddish brown with irregular pale-bordered dark blotches. Atractus echidna differs from A. iridescens by having 15 dorsal scale rows, very long tail (23.4% of SVL), and venter with irregular dark spots posteriorly (vs. 17 dorsal scale rows, tail 14–18.9% SVL in males, and venter with a median dark line along all body).

Description of holotype: Adult male, SVL 201 mm; CL 47 mm (23.4% SVL); head length 9.5 mm (4.7% SVL); head width 4.3 mm (45.3% head length); interorbital distance 3.4 mm; rostro-orbital distance 3.2 mm (0.95 times interorbital distance); naso-orbital distance 2.7 mm; head arched in lateral view, rounded in dorsal view; snout truncate in lateral view, rounded in dorsal view; canthus rostralis well marked in lateral view; cervical constriction indistinct; rostral sub-triangular in frontal view, 1.7 mm wide, 0.8 mm high, poorly visible in dorsal view; internasal 0.9 mm long, 0.7 mm wide; internasal suture sinistral with respect to prefrontal suture; prefrontal 2.1 mm long, 1.7 mm wide; supraocular sub-rectangular, 0.9 mm long, 0.5 mm wide; frontal sub-pentagonal, 2,6 mm long, 2,4 mm wide; parietal 4.0 mm long, twice as long as wide; nasal divided; nostril located between prenasal and postnasal; prenasal 0.7 mm high, about twice as high as long; postnasal 0.5 mm high, slightly higher than long; loreal 2.3 mm long, 0.4 mm high, contacting second and third supralabials; eye diameter 1.0 mm; pupil subelliptical; two postoculars; upper postocular 0.5 mm high and long, slightly longer than lower postocular; temporals 1+2; first temporal 1.5 mm long, about as long as high; upper posterior temporal elongate (3.2 mm), about three times as long as high; seven supralabials, third and fourth contacting orbit; second supralabial higher than first and smaller than third; sixth supralabial higher and seventh longer than remaining supralabials; symphisial semicircular, 1.3 mm wide, 0.4 mm long; seven infralabials, first three contacting chinshields; first pair of infralabials contacting behind chinshields; chinshields 2.4 mm long, 0.8 mm wide; three gular scale rows; three preventrals; 127 ventrals; 36 subcaudals; 15/15/15 smooth dorsal scale rows; dorsals lacking apical pits, supra-anal tubercles, and keels; eight dorsal scale rows at level of second subcaudal; body diameter 4.4 mm (2.2% of SVL); caudal spine large, conical, and acuminate.

Maxillary arch: Arched in dorsal view, with four prediastemal and two postdiastemal teeth; prediastemal teeth large, curved, well spaced, decreasing gradually in size posteriorly, angular in cross section, robust at base, narrower at apices; maxillary diastema moderately long; postdiastemal teeth half of the size of last prediastemal ones.

Colour in preservative of holotype: Dorsum of head uniformly brown; background of head uniformly brown to dorsal margin of supralabials, except for beige temporal region constituting a light temporal stripe; dorsal edge of supralabials forming a dark postocular stripe interrupted posteriorly by beige pigmentation; supralabials with diagonal invasion of brown pigment on posterior region of each scale, reaching lip margins; symphisial, infralabials, gular region, and preventrals cream with disperse brown dots; venter ground colour cream with diffuse brown spots concentrated on posterior region of body; tail light brown with irregular invasion of cream pigment anteriorly and uniformly brown posteriorly; dorsal ground colour light brown with irregular dark brown blotches decreasing in size posteriorly; anterior blotches large (four or five scales long and four to six scales wide), weakly distinct from ground colour; anterior blotches alternate and extending above first six dorsal scale rows; blotches decreasing progressively in size, posterior blotches (one scale long and wide); posterior blotches clearly distinct from dorsal ground colour, bordered by beige pigment, and disposed in two longitudinal series above fifth and sixth dorsal scale rows.

Etymology: The specific epithet “ echidna ” refers to the half woman–half snake monster goddess Echidna (Greek: ɩδνα) from Greek mythology. According to Greek legends, Echidna married the massive monster Typhon , becoming mother of all major monsters of Greek myths (e.g., Hydra, Cerberus). Her name is used herein in reference to the contrastasting anterior/posterior coloration pattern of the new species, alluding to Echidna’s hybrid nature.

Distribution: Known only from the municipality of Robles, on the southwestern portion of the department of Nariño, Pacific lowlands of Colombia. Atractus echidna apparently inhabits rainforest near sea level ( Fig. 6 ).

Remarks: On the basis of morphological similarity, A. echidna appears to be closely related to A. iridescens . In fact, most characters displayed in the holotype of A. echidna , except for some diagnostic features (see above), overlap the variation reported herein for A. iridescens . Although relative tail length, number of ventrals, and general colour pattern are susceptible to considerable intraspecific variation in Atractus , the occurance of both 15 and 17 dorsal scale rows within a single species is known only for one species (the Venezuelan A. erythromelas ) among more than 130 currently recognized in the genus. Furthermore, the two species differ in relative tail size of males, which is generally correlated with the length of the hemipenial lobes in Atractus (Passos 2008) .

Figures

FIGURE 5. Dorsal (A) and ventral (B) views of the holotype of Atractus echidna sp. nov. (UV-C 7718). SVL 201 mm, CL 47 mm.

FIGURE 6. Geographical distribution of the Atractus paucidens species group.