Gerrhopilus lestes, Kraus, 2017

Kraus, Fred, 2017, New Species of Blindsnakes (Squamata: Gerrhopilidae) from the offshore islands of Papua New Guinea, Zootaxa 4299 (1), pp. 75-94 : 89-90

Gerrhopilus lestes sp. nov.

Figs. 3 C, D

Holotype. Sex unknown (specimen undissected), BPBM 11904 (field number AA14090), collected by A. Allison on 18 January 1994 in Weitin River Valley , 13 km N, 10.5 km W of river mouth (4.5035° S, 152.9374° E, 240 m a.s.l.), New Ireland, New Ireland Province, Papua New Guinea.

Diagnosis. This species belongs to Gerrhopilus based on the presence of head glands in the centers of the anterior head shields in addition to their anterior margins ( McDowell 1974; Wallach 1996b). A relatively robust (L/ M = 76) species of Gerrhopilus having the unique combination of head glands dispersed among the rostral, superior nasal, preocular, ocular, and supraocular scales but absent from the frontal, prefrontal, and all supralabials, a rostrate snout with a transverse keel on the ventral margin of the rostral that lies dorsal to the rictus, angle of preoral snout in lateral aspect inclined at an approximately 10° angle from the horizontal, distinct pupil in the eye, longitudinal scale rows 26/24/20, transverse scale rows posterior to the rostral 722, supralabial imbrication pattern T-V, subocular scale one, presubocular scale absent, subcaudal scales 25, L/W ratio 55, and an unpigmented rostral followed sequentially by dark-brown head scales and then paler-brown body scales, giving the face a masked appearance. Refer to Table 1 for additional diagnostic qualitative and quantitative features.

Comparisons with other species. Gerrhopilus lestes may be distinguished from all other members of this genus except G. addisoni , G. depressiceps , G. eurydice , G. mcdowelli , and G. persephone in having a transverse keel on the ventral margin of the rostral, which gives the snout a beaked appearance in lateral aspect, and in having a posterior reduction of longitudinal scale rows from head to vent. It may be distinguished from G. addisoni , G. depressiceps , and G. eurydice in having 26 scale rows around the body just posterior to the head (vs. 24 in G. addisoni , G. depressiceps , and G. eurydice ) and having the snout angled at a ca. 10° angle from the horizontal, leaving the ventral keel of the rostral superior to the rictus. Gerrhopilus lestes differs from G. mcdowelli in having a much greater number of mid-dorsal scale rows (722 vs. 431–464 in G. mcdowelli ) and the rostral keel pointing directly downward (vs. pointing anteroventrally in G. mcdowelli ); and from G. persephone in its stouter habitus (L/ W = 55 vs. 82 in G. persephone ), lesser inclination of the pre-oral snout from the horizontal (ca. 10° angle vs. ca. 25° angle in G. persephone ), relatively smaller eye (L/E = 745 vs. 564 in G. persephone ), and relatively longer preoral snout (PSN/SNW = 0.68 vs. 0.44 in G. persephone ). The color pattern of an unpigmented rostral followed sequentially by dark-brown head scales and then paler-brown body scales immediately distinguishes G. lestes from all other Gerrhopilus species with a ventrally keeled rostral.

Description of the holotype. Sex unknown; specimen undissected. L = 298 mm, SVL = 289 mm, TL = 9 mm, HW = 3.6 mm, NW = 3.4 mm, SN = 1.9 mm, SW = 1.9 mm, PSN = 1.3 mm, RW = 1.60 mm, EW = 0.40 mm, W = 5.4 mm, VW = 4.1 mm, TW = 3.3 mm, L/W 55, M = 3.9 g (in preservative). Snout acutely rounded in dorsal view, rounded but with ventrally directed transverse keel in lateral view, giving rostral a beaked appearance; keel deepest medially, keratinized. Pre-oral snout inclined at 10° angle from horizontal; keel lying dorsal to rictus. Rostral large (0.44 head width), oval in shape but with dorsal sides largely parallel, posterior border extending two-thirds of distance between eye and naris, posterior margin convex; ventral surface papillose, with parallel sides, slightly concave behind keel. Nasals separated dorsally by prefrontal ( Fig. 3 C); superior nasal large, with slightly sinuous posterior margin, crescentic dorsally, acutely rounded ventrally ( Fig. 3 D). External naris compressed, oval shaped, oriented obliquely, close to rostral; superior nasal suture complete, extending horizontally from naris to rostral; inferior nasal suture complete, contacting second supralabial posterior to latter’s contact with first supralabial. Prefrontal, frontal, and interparietal all subequal in size, smaller than supraoculars and parietals, which are subequal in size; intercalary scale present between interparietal and left parietal. Preocular large, triangular; larger than ocular but smaller than superior nasal. Ocular large, smaller than preocular, extending dorsally above preocular, extending ventrally to ca. 2/3 depth of preocular, bordered posteroventrally by a subocular of less than half its size. Eye with distinct round pupil and iris, situated at widest point of ocular and approximately midway along its height, anterior 30–40% covered by preocular plate in lateral view. Supraocular barely touches eye when viewed from above. Three postoculars bordering ocular and subocular between parietal and fourth supralabial. Four supralabials, third the largest, all except first with long axis oblique to long axis of body, first an irregular tetrahedron. Supralabial imbrication pattern T-V, posterior border of second supralabial overlaps anteroventral margin of preocular, that of third supralabial overlaps anteroventral margin of subocular. Mental hexagonal, wider than long, projecting slightly beyond curve of lower jaw and fitting into notch on upper lip when mouth is closed. Infralabials two on each side.

Longitudinal scale rows 26 anteriorly, reducing to 24 by loss of two rows ca 40 mm behind tip of rostral, and reducing to 20 ca. 15 mm anterior to vent; mid-dorsal scale rows between rostral and tail tip 722; subcaudals 25; dorsocaudals 24; apical region with transverse spine directed ventrally at 90° to axis of anteroventral surface of that terminal scale (and, hence, to body axis).

Rostral, superior nasals, preoculars, oculars, and supraoculars with head glands; central glands in these shields restricted to one on each supraocular, one (left) or three (right) glands on oculars posteroventral to eyes, but otherwise arrayed along both anterior margins and throughout centers of the other scales. Glands evident only on posterior half of superior nasals because the anterior portion of those scales is unpigmented, and the glands cannot be discerned; ca. 60 glands evident on right superior nasal, ca. 50 on left. Preoculars with ca. 40 (right) and ca. 35 (left) glands in their centers. Glands elsewhere on these various scales uncountable because of fusion or blending with surrounding unpigmented areas.

In preservative, dorsum pale brown, slightly darker than ventral surfaces but no sharp demarcation between these due to gradual loss of melanin ventrally; each scale darker anteriorly. Head glands, rostral, supralabials, and lower jaw and chin unpigmented (appearing pale straw yellow under magnification). Head scales between rostral and body scales (i.e., from prefrontal to occipitals) darker brown than remainder of body, imparting to the naked eye the appearance of a mask around the eyes extending between the pale-whitish rostral and the pale-brown body ( Fig. 3 C, D). Ventral keel of rostral and tail spine dark brown. Iris black, pupil pale gray.

Etymology. The trivial epithet is a masculine Greek noun in apposition meaning “thief,” an allusion to the mask-like color pattern across the head.

Distribution. Known only from the type locality ( Fig. 2 ). The low elevation of the type locality suggests that this species is likely to occur across much of New Ireland.

Figures

FIGURE 2. Map of Papua New Guinea, showing the two known localities for Gerrhopilus depressiceps (circles) and type localities for Gerrhopilus addisoni (triangle), Gerrhopilus eurydice (square), Gerrhopilus persephone (star), and Gerrhopilus lestes (diamond). The demarcated northern portion of Papua New Guinea is the former German New Guinea from which the holotype of Typhlops depressiceps presumably came; the irregular solid line running through northwestern Papua New Guinea shows the course of the Sepik River, along which the holotype of Typhlops monochrus was presumably obtained.

FIGURE 3. Dorsal (A) and lateral (B) views of the head of the holotype of Gerrhopilus persephone holotype (UMMZ 242536); dorsal (C) and lateral (D) views of the head of the holotype of Gerrhopilus lestes holotype (BPBM 11904) showing the collar of dark color across the head. Scale bars = 2 mm.