Atractus medusa, 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 : 15-17

Atractus medusa sp. nov.

Figs. 10 , 11

Holotype: Adult male, IAvH 2981, from Playa Blanca, Gorgona Island (03º00’N, 78º12’W, ca. 0 m), municipality of Guapi, department of Cauca, Colombia, collected by J. V. Rueda (field number VR 1213).

Diagnosis: Atractus medusa is distinguished from all congeners by the combination of the following characters: (1) 17/17/17 smooth dorsal scale rows; (2) two postoculars; (3) loreal long; (4) temporals 1+2; (5) seven supralabials, third and fourth contacting orbit; (6) seven infralabials, first four contacting chinshields; (7) five maxillary teeth; (8) three gular scale rows; (9) two preventrals; (10) 133 ventrals in the single male; (11) 46 subcaudal; (12) dorsum beige with light occipital band and round dark brown blotches, decreasing in size posteriorly; (13) venter cream with diffuse dark brown dots concentrated posteriorly; (14) moderate body size, male with 325 mm SVL; (15) long tail (18.4% SVL); (16) hemipenis strongly bilobed, semicapitate, and semicalyculate.

Comparisons: Atractus medusa is distinguished from all congeners by having lobes twice as long as the hemipenial body. Additionally, A. medusa shares exclusively with A. boulengerii 17 dorsal scale rows, five or six maxillary teeth, large black band on neck, and rounded dorsal blotches decreasing in size posteriorly. Atractus medusa differs from A. boulengerii by having 133 ventrals in male, single postdiastemal tooth, and venter posteriorly black (vs. 180–189 ventrals in males, two postdiastemal teeth, and venter immaculate creamish white).

Description of holotype: Adult male, 325 mm SVL; 60 mm CL (18.4% of SVL); head length 10.5 mm (3.2% of SVL); head width 4.9 mm (47% of head length); head arched in lateral view, rounded in dorsal view; snout slightly acuminate in lateral view, rounded in dorsal view; cervical constriction barely distinct; rostral sub-triangular, 1.8 mm broad, 0.7 mm high, poorly visible in dorsal view; internasal 0.8 mm long, 0.3 mm wide; internasal suture sinistral with respect to prefrontal suture; prefrontal 2.2 mm long, 2.0 mm wide; supraocular sub-trapezoidal, 1.3 mm long, 0.6 mm wide; frontal sub-pentagonal, 2.6 mm long, 2.5 mm wide; parietal 4.1 mm long, 2.4 mm wide; nasal divided; nostril located between prenasal and postnasal; prenasal 0.6 mm long, twice as high as long; postnasal 0.3 mm high, as high as long; loreal 2.2 mm long, 0.5 mm high, contacting second and third supralabials; eye diameter 1.4 mm; pupil round; two postoculars with similar size; upper postocular 0.6 mm high, 0.4 mm long, slightly longer than lower postocular; temporals 1+2; first temporal 1.5 mm, slightly longer than high; upper posterior temporals elongate, 3.3 mm long, 0.8 mm wide; seven supralabials, third and fourth contacting orbit; second and third supralabials of similar size and higher than first supralabial; sixth higher and seventh longer than remaining supralabials; symphisial semicircular, four times broader than long; seven infralabials, first four contacting chinshields; first pair of infralabials in contact behind symphisial, preventing symphisial/chinshields contact; chinshields 2.9 mm long, 0.8 mm wide; three gular scale rows; two preventrals; 133 ventrals; 46 subcaudals; 17/17/17 smooth dorsal scale rows; dorsals lacking apical pits, supra-anal tubercles, and keels; body diameter 5.5 mm (1.7% of SVL); caudal spine moderate, conical, and slightly acuminate.

Maxillary arch: Arched in dorsal view, with five prediastemal and one postdiastemal teeth; prediastemal teeth large, well spaced, of similar size, curved posteriorly, angular in cross section, robust at base, slightly narrower at apices; maxillary diastema moderately long; postdiastemal tooth half the size of prediastemal ones.

Colour in preservative of holotype: Dorsum of head dark brown with invasion of beige pigment above latero-posterior portion of parietal, occipital, and temporal regions; background of head dark brown to the median region of supralabials, except for beige temporals; descending postocular stripe dark brown, covering postoculars, first temporal, and last two supralabials; first four supralabials with ventral margin creamins white, posterior and ventral margins of fifth supralabial marked by dark brown, sixth and seventh uniformly dark brown; infralabials, genials, and gular region predominantly creamish white, with dark brown spots above symphisial, first pair of infralabials, and anterior portion of genials; mental region cream, except for proximal region of second and third pair of infralabials dark brown; venter cream spotted diffusely with dark brown dots, concentrated on posterior third of body; tail dark brown, except for cream lateral borders of anterior subcaudals; dorsum of body with dark brown collar covering first seven scale rows; collar connected to cephalic cap; dorsal ground colour beige with 26 round black blotches alternate on the flanks; paired blotches decreasing gradually in size posteriorly; anterior blotches large (five scales long and wide), reaching paraventral region; midbody blotches (two scales long and wide), restricted to paravertebral region; posterior blotches (one scale long and wide), located above sixth scale row and scarcely distinct from the ground colour; tail dorsally uniformly beige.

Hemipenis morphology (everted organ n = 1): Organ strongly bilobed, semicapitate, and semycalyculate; lobes clearly distinct from capitulum and longer than hemipenial body; lobes attenuate, centrifugally oriented, and with flattened apices; lobes uniformly covered with concentrated spinulate calyces; capitular groove indistinct on the asulcate side and well marked on sulcate side of hemipenis; capitulum situated just above sulcus spermaticus bifurcation, longer than hemipenial body and shorter than lobes; intrasulcar region with large and narrow hooked spines; proximal area of capitulum with spinulate calyces and moderate alary spines; sulcus spermaticus bifurcates in the basal portion of hemipenial body; sulcus spermaticus branches crentrifugally oriented and running to apices of lobes; margins of sulcus spermaticus stout and moderately expanded, bordered by spinules along hemipenial body and papillae in the lobular region; hemipenial body subelliptical, broader than capitulum, covered with hooked spines; large spines concentrated laterally on basal portion of hemipenial body; basal naked pocket extending to first third of hemipenial body; proximal portion of the organ with longitudinal plicae and diffuse spinules.

Etymology: The specific epithet “ medusa ” refers to the female monster Medusa (Greek: µέδουσα) of Greek mythology. According to the Greek writer Hesiod, Medusa was one of the three Gorgons, daughters of the gods Phorcys and Ceto, their home being on the farthest side of the western ocean. Medusa had snakes for hair and her look could petrify anyone looking into her eyes, but was beheaded by the Greek hero Perseus. Herein the word alludes to the type locality of the species, Gorgona Island, an island on the western portion of the genus’ range.

Distribution: Known only from the continental Gorgona Island, municipality of Guapi, department of Cauca, Pacific region of Colombia ( Fig. 2 ).

Remarks: Despite the fact that A. medusa is described on the basis of a single specimen, it is apparently abundant on Gorgona Island (M. Rada, pers. commun.). The island is a national park of Colombia and, as a consequence, collecting is limited.

Figures

FIGURE 2. Geographic distribution of the Atractus multicinctus species group.

FIGURE 10. Dorsal (A) and ventral (B) views of the holotype of Atractus medusa sp. nov. (IAvH 2981). SVL 325 mm, CL 60 mm.

FIGURE 11. Lateral view of head of the holotype of Atractus medusa sp. nov. (IAvH 2981). Scale = 5 mm.