Gerrhopilus eurydice, 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 : 81-84

Gerrhopilus eurydice sp. nov.

Figs. 1 E, F

Typhlops depressiceps Wallach, 1996b: 110 .

Holotype. Adult female, MCZ 145954 (field number MCZ FS-F 14319 ), collected by F. Parker in Trobriand Islands, Milne Bay Province, Papua New Guinea.

Paratype. AMNH 115054 , immature, collected by F. Parker in Trobriand Islands, Milne Bay Province, Papua New Guinea, 1971.

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 large, robust (adult L/M = 44) species of Gerrhopilus having the unique combination of a rostrate snout with a transverse keel on the ventral margin of the rostral that extends to the level of the rictus, angle of pre-oral snout in lateral aspect horizontal to the body axis, a distinct pupil in the eye, anterior 30–50% of eye covered by preocular in lateral view, longitudinal scale rows 24/22/22 or 24/22/20, transverse scale rows posterior to the rostral 601–647, supralabial imbrication pattern T-V, subocular scale one, presubocular scale absent, prefrontals and supraoculars larger than frontal and parietals and interparietal, flat or convex posterior margin of the rostral, subcaudal scales 23–25, L/W ratio 55–58, 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 eurydice may be distinguished from all other members of this genus except G. addisoni , 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 2–4 longitudinal scale rows from head to vent. Gerrhopilus eurydice may be distinguished from G. addisoni by its eye having a distinct pupil (vs. eye obscure, without a distinct pupil in G. addisoni ), more robust size (L/W = 55–58 vs. 80 in G. addisoni ), and anterior 30–50% of eye covered by preocular in lateral view (vs. 67% in G. addisoni ); from G. depressiceps by its much greater relative adult mass (adult L/M = 44 vs. 70 in G. depressiceps ), anterior 30–50% of eye covered by preocular in lateral view (vs. preocular barely touching anterior margin of eye in G. depressiceps ), flat or convex posterior margin of the rostral (vs. concave in G. depressiceps ), and tail spine pointed ventrally at 90° to body axis (vs. posteroventrally at 70° in G. depressiceps ); and from G. mcdowelli by its greater length (186–319 mm vs. 94–199 mm in G. mcdowelli ), snout profile rounded in dorsal view (vs. pointed 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 = 319 mm, SVL = 310 mm, TL = 9 mm, HW = 4.6 mm, NW = 4.3 mm, SN = 2.8 mm, SW = 4.1 mm, PSN = 1.5 mm, RW = 2.45 mm, EW = 0.40 mm, W = 5.6 mm, VW = 5.0 mm, TW = 4.7 mm, L/W 57, M = 7.3 g (in preservative). Snout acutely rounded in dorsal view, rounded but with ventrally directed transverse keel in lateral view, giving the rostral a beaked appearance; keel deepest medially, keratinized. Pre-oral snout horizontal, parallel to body axis, with rostral keel extending to level of rictus. Rostral large (0.53 head width), oval in shape, posterior border extending two-thirds way between eye and naris, posterior margin flat; ventral surface papillose, with sides slightly diverging anteriorly, slightly concave behind keel. Nasals separated dorsally by prefrontal ( Fig. 1 E); superior nasal large, with slightly sinuous posterior margin, crescentic dorsally, acutely rounded ventrally ( Fig. 1 F). External naris compressed, oval shaped, obliquely oriented, close to rostral; superior nasal suture complete, extending anterodorsally at ~45° angle 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 frontal, parietals, and interparietal, which are all subequal in size. 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 greater than two-thirds its size. Eye with distinct round pupil and iris, situated at widest point of ocular and approximately midway along its height, anterior third covered by preocular plate in lateral view. Four 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, reducing to 22 by ventrolateral loss of two rows ca 18 mm behind tip of rostral; mid-dorsal scale rows between rostral and tail tip 647; subcaudals 23; dorsocaudals 22; apical region with transverse spine oriented ventrally at 90˚ to axis of anteroventral surface of that terminal scale (and, hence, to body axis).

Rostral, superior nasals, preoculars, oculars, and subocular with head glands, but these uncountable due to their faint borders and poor pigmentation around some of these glands.

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. Ventral keel of rostral and tail spine dark brown. Iris black; pupil pale gray with black circle interior to that.

Variation. This immature specimen (AMNH 115054) has a weakly keratined rostral keel. The head glands are much clearer than in the holotype; they are present in the rostral, superior nasals, preoculars (n = 29 on left, not clearly countable on right), supraoculars (n = 3 on right, 2 on left), prefrontal (n = 1), and oculars (where much fainter). Three postoculars are present on each side. Longitudinal scale rows 24/22/20; mid-dorsal scale rows between rostral and tail tip 601; subcaudals 25; dorsocaudals 21. The contrast in intensity between dorsal and ventral coloration is more pronounced than in the holotype, but this change is still gradual, with no sharp demarcation. L = 186 mm, SVL = 181 mm, TL = 5 mm, HW = 2.3 mm, NW = 2.5 mm, SN = 1.7 mm, SW = 2.2 mm, PSN = 0.9 mm, RW = 1.35 mm, EW = 0.30 mm, W = 3.2 mm, VW = 3.2 mm, TW = 3.0 mm, L/W 58, M = 1.15 g (in preservative).

Etymology. The specific epithet is the name of the oak nymph who became the wife of Orpheus, died from a viper bite, and whom Orpheus unsuccessfully attempted to retrieve from the underworld. It is a proper noun in apposition.

Distribution. Known only from unspecified localities in the Trobriand Islands, Milne Bay Province, Papua New Guinea ( Fig. 2 ).

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.