Atractus echidna

description

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 th

Pacific lowland snakes of the genus Atractus (Serpentes: Dipsadidae), with description of three new species

diagnosis

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 %

Pacific lowland snakes of the genus Atractus (Serpentes: Dipsadidae), with description of three new species

discussion

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).

Pacific lowland snakes of the genus Atractus (Serpentes: Dipsadidae), with description of three new species

distribution

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).

Pacific lowland snakes of the genus Atractus (Serpentes: Dipsadidae), with description of three new species