Atractus caxiuana Prudente & Santos-Costa, 2006

Passos, Paulo, Ramos, Luciana O., Pinna, Pedro H. & Prudente, Ana L. C., 2013, Morphological variation and affinities of the poorly known snake Atractus caxiuana (Serpentes: Dipsadidae), Zootaxa 3745 (1), pp. 35-48 : 36-42

Atractus caxiuana Prudente & Santos-Costa, 2006 ; Zootaxa 1285:22.

Figs. 1–3 , Tab. 1

Holotype. An adult male, MPEG 19964, from Estação Ecológica Ferreira Penna, Floresta Nacional de Caxiuanã (01°42’S, 51°32’W; ca. sea level), municipality of Melgaço, state of Pará, Brazil.

Paratypes. Two specimens from the same locality as the holotype. An adult female, MPEG 19657, collected by J. Bernardi at September 1999, and a poorly preserved adult male, MPEG 20128, collected by M.C. Santos- Costa at 27 January 2002.

Diagnosis. Atractus caxiuana is distinguished from all other congeners by the following combination of characters: loreal contacting the internasal (but see below); 17/17/17 dorsal scale rows with paired apical pits in both sexes and supra-anal tubercles present only in males; one or two postoculars; loreal moderately long; temporals 1+2; seven supralabials, third and fourth contacting orbit; seven infralabials, first three contacting chinshields; five or six maxillary teeth; four gular scale rows; four preventrals; 171–184 ventrals in females, 160– 162 in males; 18–24 subcaudals in females, 25–30 in males; dorsum mostly dark brown, except for dispersed beige blotches on snout, a creamy incomplete collar covering the parietal, occipital and temporal regions of the head, and two pale brown longitudinal stripes covering the centre of first two dorsal scale rows of the body; belly creamy with lateral portion of the ventral scales dark brown, forming paraventral stripes; small body size, females reaching 265 mm SVL, males 261 mm SVL; small tail length in females (9.0–9.2% SVL), moderately long in males (9.2– 13.2% SVL); hemipenis slightly bilobed, non-capitate and non-calyculate.

Variables MPEG 19964 MPEG 19657 MPEG 20128 MNRJ 3026 ICN 10114 ICN 10115 MZUSP 18892 Sex Male Female Male Male Male Female Female Tail dorsal rows 9 9 - 9 9 | 8 8 | 9 8

Ventral scales 162 171 - 162 160 184 171

Subcaudal scales 29 | 30 24 - 27 24 | 25 24 | 25 20

Postocular scales 2 | 2 2 | 2 1 | 1 2 | 2 2 | 2 2 | 2 2 | 2

SVL (mm) 261 265 - 208 165 223 101

CL (mm) 24 24 - 24 21 21 8. 5

Maxillary teeth 5 5 5 5 - 6 5

Comparisons. Atractus caxiuana is distinguished from all other congeners by usually having the internasal shields in contact with loreal scales. Occasionally, when the postnasal scale prevents this contact, there is an azygous scale between internasals modifying the orientation of the scales ( Fig. 1 ) or a slight separation between the internasal and loreal by increasing the height of the postnasal ( Fig. 2 C). Nonetheless, the lateral expansion and relative width of the internasals (with respect to the prefrontal shields) remains an autapomorphic character state of this species (see discussion). Besides the relative widening of the internasals, A. caxiuana shares a unique suite of morphological characters (e.g., presence of apical pits and supra-anal tubercles) only with A. collaris and allied species (see discussion). Atractus caxiuana differs from all of them (except A. surucucu ) in having an uniformly dark brown dorsum in adults and dark brown ventral side of the tail in juvenile and adult specimens. Atractus caxiuana differs from A. surucucu by having 171–184 ventral in females (vs. 200–207 in A. surucucu , known only from female specimens).

Description. Head twice as long as wide, slightly arched in lateral view, round in dorsal view; cervical constriction barely distinct; snout truncate in lateral view, round in dorsal view; rostral subtriangular in frontal view, wider than high, barely visible in dorsal view; internasal about twice as wide as long; posterior portion of internasal usually contacting loreal; occasionally postnasal preventing internasal/loreal contact; suture dextral or sinister with respect to prefrontal midline suture; prefrontal as wide as long; supraocular subtrapezoidal, slightly longer than wide; frontal subtriangular, as long as wide; parietal twice as long as wide; nasal completely divided; nostril situated between prenasal and postnasal; prenasal twice as high as postnasal; postnasal slightly higher than long, as long as prenasal; loreal moderately long, contacting second and third supralabials ventrally and internasal anteriorly; pupil round; usually two postoculars slightly higher than long; upper postocular generally higher and longer than lower postocular; temporals 1+2; first temporal three times as long as high; upper posterior temporals fused, about four times as long as wide; seven supralabials, third and fourth contacting orbit; first supralabial approximately half the height of second; second and third supralabials with similar height; second supralabial higher than seventh and longer than remaining supralabials; symphysial semi-circular, three or four times broader than long; usually seven infralabials, first three in contact with chinshields; first pair of infralabials in contact behind symphysial, preventing symphysial/chinshields contact; chinshields about four times longer than wide; four gular scale rows; four preventrals; 17/17/17 dorsal scale rows with paired apical pits in both sexes and supra-anal tubercles only in males; dorsal scales lacking keels; caudal spine long, conical and acuminated. Maxillary arch straight in dorsal view, with four to five prediastemal teeth and one postdiastemal tooth; prediastemal teeth decreasing in size and increasing the curvature angle posteriorly (approximately 40°); prediastemal teeth well spaced, angular in cross section, robust on their bases and narrower at apices; maxillary diastema moderately long; lateral process of maxillary bone well developed and projected posteriorly ( Fig. 1 ).

Juvenile coloration in life. Dorsum of head dark brown; snout region with creamish yellow blotches above internasals, prefrontals, and second and third supralabials; a beige blotch covering the fifth and eventually sixth supralabials; incomplete creamish yellow collar covering the temporal and occipital regions; dorsum of body, above second dorsal scale row, brown with a barely defined dark brown vertebral line (one scale wide) and paravertebral small blotches (half scale wide) on the sixth row of scales; first two rows of dorsal scales brownish gray, with the first series having posterior region cream; gular region and venter uniformly cream; ventral side of tail dark brown ( Fig. 2 ).

Adult coloration in preservative. Dorsum of head uniformly dark brown, except for snout region (internasals and prefrontals) with disperse creamy or beige (in melanistic specimens) blotches, and incomplete creamy or beige collar on neck (covering occipitals, temporals and latero-posterior region of parietals); nuchal collar (two scales long) interrupted near interparietal suture; cephalic-cap dark brown, except for creamy or beige areas covering ventral portions of second, third, fifth and sixth supralabials; seventh supralabial with posterior region creamy; infralabials and anterior third of chinshields dark brown; mid-posterior area of chinshields, gulars and preventrals creamish yellow; venter uniformly creamish yellow, except occasionally for a barely defined brown median line; lateral edge of ventral scales dark brown, forming two conspicuous paraventral lines; undersides of tail uniformly dark brown or black; dorsum of body dark brown, except for two pale brown longitudinal stripes, covering the centre of first two dorsal scale rows ( Fig. 3 ).

Hemipenial morphology (everted organ N = 2). Retracted organ (MNRJ 3026) bifurcates and extends to the level of eighth subcaudal. Fully everted and almost maximally expanded hemipenis ( Fig. 4 ) rendered a slightly bilobed, non-capitate and non-calyculate organ; lobes distinct and restricted to distal portion of hemipenial body; lobes conical, centrifugally oriented and uniformly scattered with moderate alary spines with a broad base, except for the tips of the lobes, which are covered by papillae; sulcus spermaticus divides at about half of hemipenial body; sulcus spermaticus branches with centrolinear orientation, reaching apices of lobes; margins of sulcus spermaticus stout and expanded laterally along sulcus spermaticus extension; sulcus spermaticus bordered by spinules from basal region to the tips of the organ; hemipenial body uniformly scattered with moderate hooked spines; basal naked pocket located at the right side and extending to basal region of hemipenial body; proximal region of hemipenis with longitudinal plicae and dispersed small spines. A further analysis on the hemipenis of the holotype (MPEG 19964; Fig. 3 in Prudente & Santos-Costa 2006), indicates that its lobes are not completely everted, presenting nearly flattened tips and an apparent asymmetry (the right lobe is slightly longer and wider than the left one). This organ also seems to be only partially expanded, mainly at the lobular crotch and at the bases of the lobes in its sulcate side, which hampers the observation of the spinules located at this region.

Variation. Largest male 261 mm SVL, 24 mm CL, largest female 265 mm SVL, 24 mm CL; tail 9.2–13.2% SVL (x¯ = 11.1; SD = 2.7; n = 3) in males, 8.4–9.2% SVL (x¯ = 8.9; SD = 0.4; n = 3) in females; 160–162 (x¯ = 161.3; SD = 1.5; n = 3) ventrals in males, 171–184 (x¯ = 175.3; SD = 7.5; n = 3) in females; 25–30 (x¯ = 27; SD = 2.5; n = 3) subcaudals in males, 18–24 (x¯ = 20.7; SD = 3.0; n = 3) in females; 1 (n = 3 sides) or 2 (n = 11 sides) postoculars; 8 (n = 7) or 9 (n = 6) dorsal scales rows around tail in the level of second subcaudal; 5 (n = 9 sides) or 6 (n = 2 sides) maxillary teeth; 3.3–5.0 mm body diameter. Both paratypes have dextral internasal suture with respect to prefrontal suture, while the holotype and additional specimens reported here present sinistral orientation of the internasal suture with respect to prefrontal one. The paratype MPEG 19964 has first pair of infralabials shorter, allowing a slightly contact between symphysial and chinshields. The specimen MNRJ 3026 has an azygous scale located between internasals, promoting the re-orientation of postnasal that prevents contact between internasal and loreal ( Fig. 1 ). The specimen MZUSP 18892 has a post-nasal scale barely preventing the contact between loreal and internasals, lacking the azygous internasal ( Fig. 2 ).

Distribution. Atractus caxiuana is distributed from Taraira (00º30’N, 69º40’W), department of Vaupés, Colombia; southeast to Melgaço (01°42’S, 51°32’W), state of Pará, Brazil. Atractus caxiuana occurs in rainforest environments between 0–200 m above sea level. The species´range of distribution extends more than 2,000 Km (airline) with the new records presented here, including areas above Rio Amazonas in the east of Colombian Amazonia ( Fig. 5 ).

Remarks. With respect to the possible ontogenetic change of coloration in Atractus caxiuana ( Figs. 2–3 ), although the color pattern of MZUSP 18892 (juvenile) is still evident after preservation, this specimen was recently collected (2010), while adult specimens (which do not present the paravertebral blotches) were preserved a long time ago (between 1940–1980). Therefore, we cannot establish with certainty if only immature specimens display a barely defined vertebral line and paravertebral blotches or if these features are also present in adult specimens.

Figures

FIGURE 1. Dorsal (A), lateral (B) and ventral (C) views of the head of Atractus caxiuana from Vila Cachoeira do Samuel, municipality of Porto Velho, state of Rondônia, Brazil (MNRJ 3026). The arrow indicates the azygous scale located between the internasal shields. Scale bar = 5 mm.

FIGURE 2. Dorsal (A), dorsolateral (B) and lateral (C) views of a juvenile specimen of Atractus caxiuana in life from the right bank of the Rio Madeira, municipality of Porto Velho, state of Rondônia, Brazil (MZUSP 18892). Photos by Renato Gaiga.

FIGURE 3. Dorsal (A) and ventral (B) views of an adult preserved specimen of Atractus caxiuana from Taraira, department of Vaupés, Colombia (ICN 10114). Scale bar = 10 mm.

FIGURE 4. Sulcate (A) and asulcate (B) sides of the hemipenis of Atractus caxiuana from Vila Cachoeira do Samuel, municipality of Porto Velho, state of Rondônia, Brazil (MNRJ 3026). Scale bar = 1 mm.

FIGURE 5. Geographical distribution known for Atractus caxiuana. The white dot represents the type-locality of the species.