Gerrhopilus addisoni, 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 : 80-81

Gerrhopilus addisoni sp. nov.

Figs. 1 C, D

Typhlops depressiceps Wallach, 1996b: 110 .

Holotype. Adult female, USNM 195953 , collected on 24 March 1969 by H. Heatwole on Panaete Island, Deboyne Group (10.68° S, 152.35° E; 0–50 m a.s.l.), Milne Bay 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 (adult L/M = 58) species of Gerrhopilus having the unique combination of a rostrate snout with a transverse keel on the ventral margin of the rostral that extends ventral to the rictus, angle of pre-oral snout in lateral aspect horizontal to the body axis, a vestigial eye lacking a distinct pupil, preocular covering two-thirds of the eye in lateral view, longitudinal scale rows 24/22/20, transverse scale rows posterior to the rostral 627, supralabial imbrication pattern T-V, subocular scale one, presubocular scale absent, prefrontals and supraoculars larger than frontal and parietals and interparietal, subcaudal scales 26, L/W ratio 80, and tail spine oriented ventrally at an angle of 90˚ to axis of anteroventral surface of that terminal scale (and, hence, to body axis). Refer to Table 1 for additional diagnostic qualitative and quantitative features.

Comparisons. Gerrhopilus addisoni may be distinguished from all other members of Gerrhopilus except G. depressiceps and G. mcdowelli 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 four longitudinal scale rows from head to vent. Gerrhopilus addisoni may be distinguished from G. depressiceps by its vestigial eye lacking a distinct pupil (eye well-defined and with a pupil in G. depressiceps ); anterior two-thirds of eye covered by preocular in lateral view (vs. preocular barely touching anterior margin of eye in G. depressiceps ); convex posterior margin of the rostral (vs. concave in G. depressiceps ); narrower body (L/W = 80 in G. addisoni vs. 57–67 in G. depressiceps ); prefrontal and supraoculars larger than frontal, parietals, and interparietal; and tail spine pointed ventrally at 90° to axis of anteroventral surface of that terminal scale (vs. posteroventrally at 70° in G. depressiceps ). Gerrhopilus addisoni may be distinguished from G. mcdowelli by its greater length (304 mm vs. 94– 199 mm in G. mcdowelli ), greater number of mid-dorsal scale rows (627 vs. 431–464 in G. mcdowelli ), narrower body (L/W = 80 in G. addisoni vs. 44–53 in G. mcdowelli ), pre-oral snout oriented horizontally (vs. inclined at 30° from horizontal in G. mcdowelli ), and rostral keel pointing directly downward (vs. anteroventrally in G. mcdowelli ).

Description of the holotype. Female. L = 304 mm, SVL = 296 mm, TL = 8 mm, HW = 4.0 mm, NW = 3.9 mm, SN = 2.8 mm, SW = 3.6 mm, PSN = 1.6 mm, RW = 2.30 mm, EW = 0.40 mm, W = 3.8 mm, VW = 4.3 mm, TW = 4.0 mm, L/W 80, M = 5.25 g (in preservative). Snout acutely rounded, almost pointed 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 horizontal, parallel to body axis, with rostral keel extending ventral to rictus. Rostral large (0.57 head width), oval in shape, lateral margins convex, posterior border extending two-thirds way between eye and naris, posterior margin shallowly convex; ventral surface papillose, with sides slightly diverging anteriorly, slightly concave behind keel. Nasals separated dorsally by prefrontal ( Fig. 1 C); superior nasal large, with slightly sinuous posterior margin, crescentic dorsally, acutely rounded ventrally ( Fig. 1 D). External naris compressed, oval shaped, oriented obliquely, close to rostral; superior nasal suture complete, extending anteriorly horizontally from naris to rostral; inferior nasal suture complete, contacting second supralabial just posterior to latter’s contact with first supralabial. Prefrontal and supraoculars subequal in size, larger than parietals and interparietal, which are all subequal in size. Frontal fused with left parietal. Preocular large, triangular; larger than ocular but smaller than superior nasal. Ocular large, smaller than preocular, extending dorsally well above preocular, extending ventrally to ~2/3 depth of preocular, bordered posteroventrally by subocular of less than half its size. Eye obscure, with indistinct margin and no obvious pupil, situated at widest point of ocular and approximately midway along its height, anterior two-thirds covered by preocular plate in lateral view. 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 approximately square. 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 24 anteriorly, reduced to 22 within 30 mm behind rostal (I cannot determine exact location), and reduced to 20 ca. 30 mm anterior to vent; mid-dorsal scale rows between rostral and tail tip 627; subcaudals 26; dorsocaudals 22; apical region with transverse spine directed ventrally at 90˚ angle to axis of anteroventral surface of that terminal scale (and, hence, to body axis).

Rostral, superior nasals, and preoculars with head glands; not obvious on other scales. Gland numbers uncertain due to obscure margins and poor pigmentation around many of them.

In preservative, dorsum pale brown, venter gradually becoming slightly paler due to decrease in melanin; no sharp distinction between dorsal and ventral coloration; each scale darker anteriorly. Head glands unpigmented; rostral keel and tail spine dark brown. Eye gray, very obscure; pupil not obvious.

Etymology. The specific epithet is a genitive honorific for Addison Wynn of the United States National Museum in recognition of his work on scolecophidian snakes.

Distribution and natural history. Known only from Panaete Island in the Deboyne Group of the Louisiade Archipelago, Milne Bay Province, southeast of mainland New Guinea ( Fig. 2 ). It seems likely it will be found to occur on adjacent Panapompom Island, and may occur elsewhere in the Louisiade islands.

According to field notes, the holotype was collected under the bark of a tree 4.5 m above ground.

Figures

FIGURE 1. Dorsal (A) and lateral (B) views of the head of the holotype of Gerrhopilus depressiceps (MZB 23986); dorsal (C) and lateral (D) views of the head of the holotype of Gerrhopilus addisoni (USNM 195953); dorsal (E) and lateral (F) views of the head of the holotype of Gerrhopilus eurydice (MCZ 145954). Scale bars = 5 mm.

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.