Nactus pelagicus (Girard)

Zug, George R. & Fisher, Robert N., 2012, A preliminary assessment of the Nactus pelagicus species group (Squamata: Gekkonidae) in New Guinea and a new species from the Admiralty Islands, Zootaxa 3257, pp. 22-37 : 30-31

Nactus pelagicus (Girard) – Admiralty Islands

Description. The following description derives solely from the Admiralty sample of adults (n = 21). A moderatesized, unisexual Nactus with adults ranging from 49.1–61.1 mm SVL ( Table 2), 18.1–25.2 mm (mean 21.7 mm) TrunkL, 20.3–25.1 mm (24.0 mm) SnForel, 13.2–16.8 mm (15.3 mm) HeadL, 8.5–12.0 mm (10.9 mm) JawW, 5.2– 7.7 mm (6.9 mm) HeadH, 2.9–4.3 mm (3.7 mm) EyeD, 4.2–5.6 mm (4.9 m) NarEye, 3.4–5.1 mm (4.0 mm) Interorb, and 2.0– 2.5 mm (2.3 mm) SnW.

Body proportions are: 32–42% (29%) TrunkL/SVL, 37–46% (42%) SnForel, 25–30% (27%) HeadL/SVL, 16– 21% (19%) JawW/SVL, 57–78% (70%) JawW/HeadL, 6–8% (7%) EyeD/SVL, 17–29% (24%) EyeD/HeadL, 31– 34% (32%) NarEye/HeadL, 23–30% (26%) Interorb/HeadL, 13–17% (15%) SnW/HeadL.

Head scales small and granular except for enlarged scales bordering nares and mouth. Large horizontal trapezoidal rostral scale without middorsal notch, cleft on midline of middorsal half and distinctly depressed on its midposterior two-thirds; 3–4 large supralabials (Suplab) and 3 infralabials (Inflab) in front of anterior edge of orbit, first supralabial and second infralabial largest of respective series. Nasal scale contacts first supralabial, rostral, supranasal, and posteriorly 2–3 granular loreal scales, dorsalmost one largest (> 2X). Supranasals moderate sized, rectangular to semilunate in contact on midline. Scales on outer edge of eyelid slightly enlarge forming low crenate border. Chin with large trapezoidal mental and small to medium-sized postmentals (PostM = 8–18). Dorsum of neck and trunk with numerous rows of enlarged tubercles from nape unto tail; on trunk rows reach ventrolaterally to edge of venter, 12–19 entire rows (DorsTub), and only to mid-laterally on neck; tubercles in each row usually separated by one or two granular scale yielding 28–37 tubercles per row (TUBROW); 8–10 rows transversely between hindlimbs (TUBHIP). No tubercles on dorsal surface of forelimb; hindlimb with numerous tubercles (Tub- Hindl usually 2), and tubercles density low fore and aft (TubDens = 0). Tail base with tubercle rows dorsally and laterally. Tail covered with uniform small keeled scales dorsally and ventrally (Subcaud = 0). One or 2 cloacal spurs (CloacS); distal edge usually truncate (CST = 0). Ventral scales from chin to vent small, granular and variable surfaced, smooth to weakly bicarinate. Forefoot with narrow digits, their lengths typically 2≈3>4>1≈5; 18–21 lamellae beneath fourth digit (4FingLm), 6–7 scale rows between lamellae at base of first and fifth fingers (Palm). Hindfoot with narrow digits, their lengths usually 3>2≈4>5>1; 21–26 lamellae beneath fourth digit (4ToeLm); lamellae of first digit extend onto sole of foot to its heel as row of greatly enlarged scales.

In preservative, ground color medium brown with narrow dark brown transverse bars on neck to base of tail; bars usually bordered posteriorly by narrow beige bar. Venter uniform medium brown from chin to base of tail.

Comparison to Fijian Nactus pelagicus . With a sample (n = 21) composed entirely of females and collected by multiple collectors over several decades, we propose that the most abundant Admiralty Nactus is an alien species and, specifically, is N. pelagicus . The earliest collection for this morphotype in the Admiralties is 1969 (see below in following section).

Our comparison of the Admiralty sample is limited to a Fijian one. Fiji is the origin of the type series of N. pelagicus , roughly in the center of the N. pelagicus distribution, and has a morphology characteristic of N. pelagicus taxon ( Zug & Moon 1995). In mensural features ( Table 2), the Fijian and Admiralty samples are generally similar or identical in means. The proportions offer the easiest comparison and more readily reveal differences. TrunkL/SVL ( Fiji mean 42% vs. Admiralty 38%), EyeD/HeadL (28%, 23%), and Interorb/HeadL (31%, 26%) are the only proportional traits with means differing by more that 2%. These differences might suggest derivation of the two samples from different taxa; however, the number of similarities suggests otherwise, and the result is potentially due to sampling differences or measurement differences (Fijian sample measured in early 1990s, the Admiralty sample January 2011). While EyeD/SVL (7.5%, 6.5%) does not display a great difference in eye size, the EyeD and Interorb size relative to HeadL does indicate some difference in head morphology between the Fijian and Admiralty samples. This difference in comparison to the high similarity of the two samples seems inadequate to negate our hypothesis that the Admiralty ‘ pelagicus ’ is an introduction from Oceania.