Atractus attenuatus, MYERS & SCHARGEL, 2006

MYERS, CHARLES W & SCHARGEL, WALTER E, 2006, Morphological Extremes-Two New Snakes of the Genus Atractus from Northwestern South America (Colubridae: Dipsadinae), American Museum Novitates 3532 (1), pp. 1-16 : 2-8

Atractus attenuatus , new species

Figures 1–3 , Map 1

HOLOTYPE: AMNH R-19998, an adult male obtained by Hermano Nicéforo María on May 16, 1921, at Sabanalarga, on Cauca River, [6 ° 51 9 N, 75 ° 49 9 W, Department of Antioquia], Colombia. The type locality, Sabanalarga ( Nicéforo María, 1942: 87, map), lies on the east bank of the Río Cauca at an elevation of about 1000 m ( Paynter, 1997: 372), in the northern end of the Cordillera Central.

ETYMOLOGY: The species name attenuatus is the passive past participle of the Latin verb attenuo (to stretch or make thin), and also (as used here) a derived adjective meaning stretched out and slender.

DIAGNOSIS: Atractus attenuatus is distinguished by its exceptionally slender, drawnout habitus, combined with 17 scale rows, a high ventral + subcaudal count (226), and an extremely vague pattern of numerous, closely spaced, indistinct crossbars. The most relevant comparison is with Atractus sanguineus , which has fewer, more widely spaced crossbars that are distinctly darker than the ground color and that are connected by a vertebral dark line. In life, the dorsal ground color of A. attenuatus is probably brown, whereas A. sanguineus is red. See Comparisons.

DESCRIPTION OF HOLOTYPE

The specimen is a male judged to be adult because the hemipenial spines are mineralized. It is fairly well preserved, undissected except for the tail, and the stratum corneum is largely intact. See table 1 for detailed measurements.

PROPORTIONS AND SCUTELLATION: Total length 420 mm, tail length 66 mm (15.7% of total). Elongated and slenderly proportioned (fig. 1). Body slightly wider than high, round- ed ventrolaterally; greatest head width 70.1% of head length from snout to end of parietals and 57.3% of length from snout to end of mandible; head width and greatest body width each 1.7% of SVL. Dorsal scales smooth, lacking apical pits, in 17-17-17 rows. Ventrals 178, anal plate undivided, subcaudals in 48 pairs.

Head (fig. 2) barely wider than neck; snout bluntly rounded in dorsal view, rounded in profile; rostral wider than high, visible from above; internasals small, as wide as long, less

TABLE 1 Measurements a (in mm) of Holotypes of Atractus attenuatus and Atractus gigas than half (44%) the length of prefrontal suture; prefrontals large, longer than wide (greatest prefrontal width 80% of greatest length); prefrontal suture asymmetrical, noticeably dextral to the internasal suture; prefrontal suture 83% length of frontal plate; supraoculars large, nearly as broad as long; frontal as long as broad, roughly pentagonal in shape; interparietal suture slightly longer than prefrontal suture, 87% of frontal length.

Eye moderate, contained 1.4 times in loreal length, 2.8 times in snout length (sagittal); eye length slightly smaller (93%) than distance to lip; eye not protuberant to edge of lip and not visible from below. Nasal divided above and below naris, its greatest length 90% of loreal length; loreal long, 2 times longer than greatest height, well separated from internasal, entering eye; no preoculars; supralabials 7, 3rd and 4th each as wide as high and touching eye; 6th supralabial on right side separated from lip by an aberrant anteroventral projection of 7th labial; postoculars 2, subequal; temporals 1 + 2, the upper one in row 2 elongated, reaching past end of parietal.

Infralabials 7, first pair in contact behind mental, first three in contact with genials; single pair of large genials, 2.5 times longer than wide; three large median gulars or preventrals between genials and 1st ventral. Head plate tubercles tiny, inconspicuous, most concentrated on rostral plate, otherwise sparse.

COLOR PATTERN: The specimen in preservative (fig. 1) is medium brown dorsally, somewhat lighter on the lower two scale rows, with an extremely vague pattern of narrow dorsal crossbars. 3 The indefinite crossbars are narrow (about 2–3 scales wide) and closely spaced (about 1 scale apart), and extend to about the 4th or 5th scale row on each side. Although impossible to count accurately, there are an estimated 95 dorsal crossbands on the body; there are an indefinite two or three such markings on the base of the tail, which otherwise is patternless.

Top of head brown like body, vaguely mottled, becoming paler yellowish brown on lower three-fourths of supralabials and beneath head and neck. The venter becomes increasingly and irregularly blotched with light brown posteriorly; subcaudal surfaces nearly uniform light brown.

MAXILLO- PALATO- PTERYGOID ARCH: Some teeth on each side are broken; the left maxilla itself is broken, as is the right ectopterygoid. Description is of right side in situ. Maxilla rather robust, weakly arched, extending anteriorly to first supralabial, with 10 recurved

3 The crossbarred pattern is best visualized by the naked eye, with the specimen immersed in alcohol. The indefinite markings virtually disappear when the specimen is viewed under a dissecting microscope. The vagueness of this pattern does not seem to be the result of fading in preservative, and the pattern was probably indistinct in life.

19998), shown 1.5 times life size.

teeth, large anteriorly, decreasing in size posteriorly. Anterior 8 teeth closely to moderately spaced, not firmly ankylosed, with alternate teeth represented only by sockets; teeth rounded in cross section (lacking an angular edge on labial side). A gap between the small teeth (9–10), these posterior two teeth broken but apparently much smaller than those anteriorly. Maxilla extending posteriorly past small teeth as a short toothless process. An expanded curved flange on maxilla extending mediad and ventrad; anterior edge of flange adjacent to ultimate small tooth, with most of flange lying posterior to the small teeth. Ectopterygoid (broken; described from left side) weakly and shallowly bifurcated, the ventromedial branch being more robust; ectopterygoid fork braced against posterior half of flange on maxilla. Palatine lacking a maxillary process.

HEMIPENIS: Before removal, the left retracted hemipenis of the holotype bifurcated at the level of the middle of subcaudal 8 and terminated at the end of subcaudal 9, with the two slips of retractor muscle merging at the middle of subcaudal 11 and the muscle originating at the end of subcaudal 30. Although the lobes of this bifurcated hemipenis were equal in length and width, the dorsal lobe was noticeably higher than the ventral lobe, with a more massive appearance (the size differential was not noticeable after eversion); the lobes appear equal in the right hemipenis as examined in situ.

The left hemipenis was removed and the retractor muscle was severed across the insertion slips close to the lobes. The organ was immersed for 3.5 hours in a 2% solution of potassium hydroxide (KOH), after which it was moved to 3% KOH for another 3 hours to hasten the softening process. It was then everted with forceps; the tips of the lobes were pushed out using the round head of an insect pin. Finally, the organ was inflated with carmine-dyed petroleum jelly for study and illustration.

The manually everted left hemipenis (fig. 3) is 12.9 mm long, with lobes comprising about 30% of its length. The sulcus spermaticus divides about 8 mm (62%) above the base, with the branches extending in centrifugal orientation to the tips of the lobes. The organ is noncapitate.

The hemipenial lobes are completely covered by papillate calyces, which extend proximally between the sulcus branches to the fork. Two rows of small spines below the sulcus branches extend chevronlike to the sides of the organ; these rows do not retain their integrity on the asulcate side, which bears small spines immediately below the lobes. The midsection of the hemipenis is encircled by numerous mediumsized spines, which decrease in size proximally; no large spines. Except for being nude at the base, the proximal 30% of the organ is spinulate. A nude pocket is present on the basal side (dextral to sulcus spermaticus), extending distad nearly to the edge of the spines.

DISTRIBUTION: Atractus attenuatus is known only from its type locality in the Río Cauca drainage, about 1000 m elevation, on the western side of the northern end of the Cordillera Central (map 1) .

COMPARISONS

Very few Atractus have such a strikingly slender habitus, the main exception we are aware of being Atractus sanguineus Prado (1944, 1946 ). This species also is known only from its holotype (a male 424 mm in total length), whose size and scutellation are comparable to A. attenuatus . 4 Each has a high ventral + subcaudal count (222 in sanguineus , 226 in attenuatus ), and sanguineus appears to be similarly attenuated based on a photograph published first with the original description ( Prado, 1944) and later reprinted ( Prado, 1946). The second printing was of better quality and is reproduced here as figure 4.

It is evident from comparisons of photographs (figs. 1, 4) that the dorsal crossbars are fewer, more widely spaced, and more pronounced in A. sanguineus , which also has these markings interconnected by a vertebral dark line that is lacking in A. attenuatus . Atractus attenuatus has a ground color of medium brown in preservative and presumably was similarly colored in life, 5 whereas the lighter ground color of the preserved specimen of A. sanguineus was described by Prado (1944, 1946) as vermelho-sanguinea (blood-red). Daniel (1949: 317) later also commented on the red color of the sanguineus holotype.

Atractus attenuatus and A. sanguineus are geographic neighbors in northern Colombia. Their type localities are only 46 km apart, but at different elevations and on opposite sides of the northern end of the Cordillera Central. Atractus sanguineus came from Yarumal (2300 m fide Paynter, 1997: 471) on the eastern side of the Central Andes, whereas A. attenuatus is from Sabanalarga, at a lower elevation (1000 m) on the western side.

4 Prado noted 3 infralabias em contacto com a mental, but, from his various descriptions of Atractus spp. , it is clear that he used the term ‘‘mental’’ for the paired genials. Atractus normally has on each side 3 or 4 infralabials in contact with the single pair of genials, with the 1st pair of infralabials usually in contact behind the azygous mental plate (e.g., fig. 7B).

5 Medium brown pigmentation usually changes relatively little in preservative unless faded in light.

Map 1. Type localities of the new species in the northern Andes. Atractus attenuatus in the northern end of the Cordillera Central, Río Cauca drainage, Colombia. Atractus gigas on the Pacific versant of western Ecuador. The symbol over the Atractus attenuatus locality nearly overlaps the type locality of A. sanguineus Prado , 46 km northeastward, at a higher elevation on the opposite side of the Cordillera Central.

Moreno interpreted as Sabanalarga at an elevation below 100 m in the Department of Atlántico, on the north coast of Colombia. However, the specimen and locality were provided by Brother Nicéforo María, who mapped his locality as being the Sabanalarga that is situated much higher in the Cauca Valley ( Nicéforo María, 1942: 87); Paynter (1997: 372) provided an elevation of 1000 m. Nicéforo María had sent to the American Museum unidentified specimens that were not included in his 1942 report, which recorded only Mastigodryas pleei (as Dryadophis ) and Bothrops atrox from Sabanalarga.

REMARKS

The holotype of Atractus attenuatus (AMNH R-19998) inexplicably was catalogued originally as ‘‘ Atractus major ’’, a reasonably well-known Amazonian snake. It remained under that suspect identification for decades, until curatorial attention was given to the AMNH Atractus collection. Pérez-Santos and Moreno (1988: 86) commented on the specimen as A. major without indicating that they had not examined it. 6 The catalogued locality was ‘‘Sabanalarga, on Cauca River’’, which Pérez-Santos and

6 Pérez-Santos’ visits to the American Museum were spent in copying geographic records; he unfortunately never got time to examine specimens and confirm names. It is a regrettable fact of life that all major museum collections have many specimens bearing identifications that are out of date or obviously wrong to begin with.

Figures

Fig. 1. Atractus attenuatus, new species. Dorsal and ventral views of the adult male holotype (AMNH R-

Fig. 2. Atractus attenuatus, new species. Head of holotype (AMNH R-19998), X5.

Fig. 3. Everted hemipenis of Atractus attenuatus, new species, in sulcate and asulcate views. Left organ of holotype (AMNH R-19998), X8.9. (Laboratory preparation from hemipenis preserved in retracted condition; fully everted but not necessarily completely expanded.)