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Arcanumophis problematicus (MYERS, 1986)

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Higher TaxaColubridae (Dipsadinae), Colubroidea, Caenophidia, Alethinophidia, Serpentes, Squamata (snakes)
Common NamesE: Problem Ground Snake 
SynonymLiophis problematicus MYERS 1986
Erythrolamprus problematicus — GRAZZIOTIN et al. 2012
Liophis problematicus — WALLACH et al. 2014: 385
Arcanumophis problematicus — SMAGA et al. 2019 
DistributionPeru (Puno)

Type locality: "at 1520 m above sea level at San Juan, Tambopata [Río], Sandia [Province of], Department of Puno, Peru. (=San Juan del Oro, about 30 km ENE of the town of Sandia, on the west bank of the Río Tambopata—at 14˚13' S, 69˚10' W.)" [given as 14.21667°S, 69.16667°W by Smaga et al. 2019]  
TypesHolotype: FMNH 64733, a 275 mm male (H.H. Heller, Nov. 22-Dec. 20, 1950). 
DiagnosisDiagnosis (genus). Arcanumophis gen. nov. differs from all other Xenodontini by the presence of a crease on the rostral scale, here interpreted as an autapomorphic condition. Molecular data support A. problematicus as an independent lineage, sister taxon to all other species of Xenodontini (see Discussion in Smaga et al. 2019).

DESCRIPTION: The holotype (fig. 1) is an adult male as determined by enlarged and convoluted vasa deferentia, enlarged segments of the kidney tubules, and hardening of the hemipenial spines. The specimen is in fair condition ex- cept for a slightly misshapen mouth border in the rostral region and front of the lower jaw, owing to desiccation. (Myers 1986)

PROPORTIONS AND SCUTELLATION:A small, slender, short-tailed snake, 275mm total length, 51mm tail length (tail 18.5%of total). Body higher than wide (roughly 6.5mm x 5.5 mm), rounded ventrolaterally. Head slightly wider than body; greatest head width (parietal region) 6.5 mm, head length 11.3 mm from tip of snout to level of end of man- dibles.Diameter of eye greater than distance from its anterior edge to anterior edge of naris, extending 1.5 times into length of snout. Dorsal scales smooth, lacking apical pits and anal ridges, in 19-17-17 rows; scale-row reduction from 19 to 17 rows by fusion of lat eral rows 3 + 4, on both sides, at level of 62nd ventral. Two preventrals (undivided gulars), 133 ventrals, divided anal plate, 36 pairs of subcaudals. Rostral plate visible from above, about 2.5 times wider than high, showing a blunt horizontal keel (fig. 2) that may be an artifact.3 Paired internasals, each wider than long, about three-fourths as long as prefrontals. Paired prefrontals, each wider than long, each in contact with its mate and with frontal, supraocular, preocular, loreal, nasal, and in ternasal (left prefrontal in contact with both left and right internasals). Frontal hexagonal (with small anterior apex), 2.0 times longer than its greatest width, 1.5 times longer than distance from its anterior edge to tip of snout. Supraoculars posteriorly more than one-half of frontal width, narrowed anteriorly. Parietals about 1.7 times longer than broad; in terparietal suture shorter than length of snout, about 60 percent length of frontal plate. Large nasal plate, in contact with first two supralabials, grooved apparently above and below naris; small loreal plate ovoid, separated from eye by the single high preocular (no subpreocular); two postoculars, the upper twice the size of lower. One large anterior temporal and upper and lower posterior temporals, be tween labials 5-7. Supralabials 7, second touching loreal, third and fourth bordering orbit. Infralabials 8, first pair in contact behind mental, 1-4 touching an anterior genial, 4-5 touching a posterior genial. Genials well developed; anterior pair slightly shorter than posterior pair but with longer intergenial suture. Inconspicuous tubercles (presumed sen sory organs) sparsely present on head plates. (Myers 1986)

COLORATION: Body light brown, with darker middorsal brown (gray) streak and lateral and ventrolateral blackish brown lines (fig. 3), as follows: (1) The middorsal streak is medium brown (gray after loss of stratum corneum) and extends from the nape to the end of the tail; this dark streak is five scales wide on the neck, three scales wide on the greater length of the body, and narrows grad ually on the tail. (2) The dark lateral line extends from the rear of the head to the tip of the tail, becoming darker (brown to black ish brown), more nearly continuous (broken at anterior end), and widening perceptibly from anterior to posterior. The lateral line lies on only the lower edge of scale row 6 anteriorly, then drops (because of scale row reduction) onto row 5 before midbody; it covers the lower half of row 5 at midbody, nearly all of row 5 toward the end of the body, and continues conspicuously along the side of the tail, where it narrows only toward the end. (3) Brown pigmentation extends from the lower sides onto the ventral and subcaudal plates before ending abruptly at a blackish brown ventrolateral line that extends from the head to the end of the tail. The median three-fifths of the ventral surface is immaculate white in preservative, and sharply set off by the dark ventrolateral line on either side. The head is brown (gray under stratum corneum) above, irregularly blotched with dark er brown, and set off posteriorly by several white markings (fig. 4) as follows: (1) A small white spot immediately behind the interparietal suture occupies less than half the area of the first dorsal scale. (2) A pair of obliquely arranged white nape spots lie one scale behind the parietal plates and are separated by the width of the brown vertebral scale row; each of the large nape spots occupies all or parts of 6-7 scales. (3) A rounded white spot, occupying parts of three scales, lies on each side of the neck immediately posterior to the last supralabial and narrowly separated from the nape spot above. There is no dark stripe through the eye. The supralabials bear three conspicuous white markings that are broadly edged in dark brown, as follows: There is a short horizontal white line across labials 1-3; a small subocular white area on labial 4; and a bold post ocular white stripe that originates on the low er postocular and extends obliquely across labials 5, 6, and lower corner of 7 to the edge of the mouth, where the line matches up with a white line on the anterior part of the last (8th) infralabial. The underside of the head is basically white, with brown blotches on the mental and on each of the infralabials and genials and on many of the gular scales. (Myers 1986)

DENTITION: There are 15 (right side) or 16 (left) recurved subequal maxillary teeth, which are followed by a distinct diastema and two ungrooved fangs that are about 1 ½ times larger than the prediastemal teeth (fig. 5). The ultimate prediastemal socket on each side lies anterior to the front edge of the ectopterygoid process. The fangs have a rounded anterior surface, a flattened knifelike posterior edge, and are somewhat laterally compressed at the tips; the ultimate fang is offset slightly laterad. The numerous palatine-pterygoid teeth are not readily counted in situ. There are at least 26 teeth on the left dentary. (Myers 1986)

COMPARISONS: Externally, Liophis problematicus is quite different from its presump tive intragroup relatives, which are mostly much larger snakes. The species of Erythrolamprus are brightly ringed coral snake mim ics, whereas the usually crossbanded, heavy bodied Xenodon and Waglerophis resemble terrestrial vipers. The species of Lystrophis are crossbanded or blotched and have an upturned transversely keeled rostrum that is supported above by a longitudinal median keel. Umbrivaga is characterized by a low number of subcaudals as is Liophis problematicus, and one species is as small as prob lematicus; however, the species of Umbri vaga have stripes confined posteriorly on body and tail, with spots or bands anteriorly on the body, and pale supralabials. The preceding genera also differ from L. problematicus in various kinds of maxillary specialization. Some of the characters alluded to above (as well as characters not mentioned) are doubtlessly synapomorphic, and I find no grounds for assigning the new snake to any of the five considered genera. This leaves Liophis (sensu Dixon), which Dixon (1980, p. 26) recognized as the "most generalized genus of the group in its osteology, external morphology, habitat, and food preferences." As now constituted, Liophis is extraordinar ily diverse: The species range in habitus from slender to relatively robust; adult total length varies from small (e.g., <500 mm in L. williamsi) to large (e.g., >1 m in L. miliaris); the tail is short to long (tail/total length = 0.135-0.310 fide Dixon); color patterns in clude unicolor, speckled, banded, and several distinctive types of striping, including combined patterns such as anterior blotches and posterior stripes. The rather extreme diversity raises a suspicion that Liophis may be polyphyletic. Most of the dentitional and other osteological traits used by Dixon to distinguish Liophis from related genera seem to be plesiomorphic, and it is perhaps the one genus of the group that lacks obvious synapomorphies. [...]
Aspects of the color pattern of problematicus are distinctive among Liophis, few of which show any tendency toward pale nape spots or pale labial markings. The head pattern of Liophis problematicus is more similar to some species of Rhadinaea (e.g., compare fig. 3 with Myers, 1974, fig. 26) than to any Liophis. Most species of Liophis have the upper lip basically pale, although some have dusky labials owing to a suffusion of melanophores; only a few species have dark su pralabials with definite pale markings, which usually take the form of a horizontal stripe or line, in contrast to the oblique markings in problematicus. One such species characterized by a white labial line is Liophis williamsi, which, like Liophis problematicus, is a small snake that might also be (and has been) confused with Rhadinaea. (Myers 1986) 
CommentKnown from only 2 specimens.

Type species: Liophis problematicus MYERS 1986 is the type species of the genus Arcanumophis SMAGA et al. 2019.

Distribution: see map in Moraes et al. 2021 for localities. 
EtymologyNamed after the Greek problematikos (problematical),an adjective used in reference to uncertain kinship.

The genus was named after Latin arcanum, meaning mystery and Greek ophis, meaning serpent. 
  • Dixon, James R. 1989. A key and checklist to the neotropical snake genus Liophis with country lists and maps. Smithsonian Herp. Inf. Serv. (79): 1-40 - get paper here
  • Grazziotin, Felipe G.; Hussam Zaher, Robert W. Murphy, Gustavo Scrocchi, Marco A. Benavides, Ya-Ping Zhang and Sandro L. Bonatto 2012. Molecular phylogeny of the New World Dipsadidae (Serpentes: Colubroidea): a reappraisal. Cladistics DOI: 10.1111/j.1096-0031.2012.00393.x - get paper here
  • Moraes, Leandro J C L, Omar M Entiauspe-Neto, Rafael de Fraga, Igor Y Fernandes, and Fernanda P Werneck. 2021. Systematics of the Rare Amazonian Genus Eutrachelophis (Serpentes: Dipsadidae), with an Emended Diagnosis for Eutrachelophis Papilio. Zoologischer Anzeiger 295: 191–204 - get paper here
  • Myers, C W 1986. An enigmatic new snake from the Peruvian Andes, with notes on the Xenodontini (Colubridae: Xenodontinae). American Museum Novitates (2853): 1-12 - get paper here
  • SMAGA, CHRISTOPHER R.; ALEX TTITO, ALESSANDRO CATENAZZI 2019. Arcanumophis, a new genus and generic allocation for Erythrolamprus problematicus (Myers 1986), Xenodontinae (Colubridae) from the Cordillera de Carabaya, southern Peru. Zootaxa 4671 (1): 129–138 - get paper here
  • Wallach, Van; Kenneth L. Williams , Jeff Boundy 2014. Snakes of the World: A Catalogue of Living and Extinct Species. [type catalogue] Taylor and Francis, CRC Press, 1237 pp.
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