Nactus sphaerodactylodes, Kraus, Fred, 2005

Kraus, Fred, 2005, The genus Nactus (Lacertilia: Gekkonidae): a phylogenetic analysis and description of two new species from the Papuan Region, Zootaxa 1061, pp. 1-28 : 8-17

Nactus sphaerodactylodes sp. nov.

Figs. 2–4 , 5A

Holotype: BPBM 20764 (field tag FK 9887), adult male, collected by local villagers at Araeda, Sudest Island, 11.43624 S, 153.43008 E, 1­20 m elevation, Milne Bay Province, Papua New Guinea, 28 April 2004.

Paratypes: BPBM 20760­63, 20765­75, 21692­96 (the last five to be repatriated to PNGNM), same data as holotype; BPBM 20757, same data as holotype except collected by F. Malesa 10 April 2004; BPBM 20758, same data as holotype except collected by F. Kraus 12 April 2004; BPBM 20759, same data as holotype except collected 13 April 2004; BPBM 20776­80, same data as holotype except collected 29 April 2004.

Referred specimens: BPBM 20756, collected by F. Malesa at Somusomuwa, Misima Island, 10.63791 S, 152.82821 E, Milne Bay Province, Papua New Guinea, 8 April 2004. BPBM 17707, collected by A. Allison at Guasopa, Woodlark Island, 9.2233 S, 152.9433 E, Milne Bay Province, Papua New Guinea, 24 January 2003.

Diagnosis: A small (SV = 20.4–26.0 mm, mean 24.2 mm) species of Nactus lacking dorsal tubercles; and having granular, largely tricarinate dorsal ( Fig. 2 ) and ventral scales; lamellate, unexpanded subdigital lamellae; 10­13 lamellae under the 4th toe; a single row of scales between the orbit and supralabials; claws lying within four scales; granular postmentals; elongate first infralabials; 4–5 supralabials to center of eye and 6–7 to rictus; 5–7 infralabials; enlarged postnasals; smooth scales on the tail; oval ear opening; relatively broad head (HW/HL = 0.71–0.79); short, broad snout (EN/SV = 0.070–0.086, IN/SV = 0.038–0.049, EN/IN = 1.5–2.1); large eye (EE/SV = 0.085–0.103) and interorbital distance (ID/SV = 0.063–0.083); relatively broad tail (TW/TL = 0.12–0.16); four sternal/ xiphisternal ribs; and dark brown dorsal color, usually with scattered, obscure darker and lighter brown punctations and irregular markings, these sometimes coalescing to form obscure, irregular chevrons.

Comparison with other species: Nactus sphaerodactylodes may be distinguished from all other members of the genus except N. coindemirensis in 1) lacking rows of enlarged tubercles on the body, 2) having the claws lie within four (vs. two or three) scales, 3) having short digits, with 10–13 lamellae under 4th toe (vs. 15–25); and 4) having elongate infralabials such that the mental extends no further posteriorly than the center of the first infralabials (vs. to or past suture with 2nd infralabial) and the suture between the first and second infralabials lies behind the center of the second supralabial (vs. at beginning of second supralabial). From N. coindemirensis , N. sphaerodactylodes differs in the last two characters above as well as in having granular (vs. imbricate) ventral scales, carinate (vs. smooth) dorsal and ventral scales, lamellate (vs. granular) distal subdigital scales, unexpanded (vs. expanded) proximal subdigital lamellae, and 5–7 (vs. 10–11) infralabials. From the closely related N. vankampeni , N. sphaerodactylodes further differs in having tricarinate (vs. multicarinate) dorsal and ventral keeling, one (vs. two) scale row between orbit and supralabials, and four (vs. five) sternal/xiphisternal ribs.

Description of holotype: An adult male with right lateral incision; part of liver removed. Animal small (SV = 22.0 mm, TrL = 9.3). Head relatively long (HL/SV = 0.27) and wide (HW/HL = 0.78), not depressed (HH/HL = 0.47), distinct from neck ( Fig. 3A ). Loreal and interorbital region slightly inflated; canthus rostralis absent. Snout relatively long (SN/HL = 0.41), much longer than eye diameter (SN/EY = 2.2) ( Fig. 3 B). Eye relatively large (EY/HL = 0.19); pupil vertical, with crenellated margins; supraciliaries small, conical, not well differentiated from adjacent granules. Ear opening small (Ear/HL = 0.068), oval, with long axis running posterodorsal to anteroventral; distance between ear and eye twice eye diameter. Rostral half (0.55 mm) as high as wide (1.1 mm), highest just medial to nares and depressed between these points; length (<0.5 mm) slightly less than height; partially divided dorsally by weak rostral groove. Two enlarged supranasals separated by three granular internasals. Rostral in contact with first supralabials, two supranasals, and three internasals. External nares oval, long dimension running anterodorsally to posteroventrally; each bordered by rostral, supranasal, first supralabial, and one nasal. First supralabial has an extension that reaches dorsally to behind the posteriormost limit of the naris. Nasal bordered posteriorly by two small granular scales. One row of small scales separates orbit from supralabials. Mental subtriangular, wider (1.3 mm) than long (1.1 mm). No enlarged postmentals ( Fig. 3 C); mental bordered posteriorly by nine tiny granules. Infralabials bordered by tiny granules, these somewhat larger posteriorly than anteriorly. Supralabials to mid­orbital position four on each side, to angle of jaw six on each side. Infralabials seven on right, six on left. Scale rows between center of orbits ~36.

Body rather slender (TrL/SV = 0.42), lacking ventrolateral folds ( Fig. 5A ). Dorsal scales on head, body, and limbs tiny, conical, juxtaposed granules; each wider than long and with three sharp keels; granules on neck also usually higher than long; granules on venter longer than wide or roughly circular; otherwise, granules quite homogeneous. Organs on posterior end of each scale 3. Enlarged tubercles absent on head, body, and limbs.

Precloacal pores in a shallow V­shaped series ( Fig 3 D), 16, asymmetrically distributed with 12 on right side of apex of V and 4 on left, followed by a gap of 8 (left) or 10 (right) rows of enlarged femoral scales lacking pores, followed by 4 femoral pores on each side. Granules anterior to precloacal pore series and those in anterior femoral region enlarged relative to those on abdomen; granules immediately posterior to pore series conspicuously smaller. No precloacal groove. Scales on palms and soles rounded, smooth.

Fore­ and hindlimbs relatively short, stout (FA/SV = 0.13, CS/SV = 0.17). Digits short, only modestly reflected at basal interphalangeal joints; all with robust, slightly recurved claws. Subdigital lamellae narrow, smooth, rounded, and slightly expanded distally. Lamellae on manus 4­7­8­8­6 on right, 5­6­9­9­7 on left; on pes 5­8­11­11­11 on right, 5­7­10­12­11 on left. Relative lengths of digits on manus I <V <II <III <IV; on pes I <II <V <III <IV. No interdigital webbing present on manus or pes.

Tail relatively short (TL/SV = 0.96), with moderately wide base (TW/TL = 0.12), tapering to a point, slightly constricted at base. Cloacal sacs well­developed, external orifices large, approximately 3 scales in width, situated near lateral margins of vent. Scales of tail large, flat, smooth, imbricate; a pair of enlarged, rounded postcloacal spurs on each side of tailbase, the dorsal smaller than the ventral.

Color in preservative: Dorsal granules brown, each granule with 0–8 small black spots; keels of granules frequently margined with dark brown but often not. Interstitial skin darker brown. A few scattered granules light gray. Overall appearance is of a uniformly drab brown color. Rostral and labials chocolate brown with wide unpigmented strips along margins. Granules of venter much like those on dorsum except that many more are light gray, imparting to the venter an overall salt­and­pepper appearance. Light scales on chin and throat typically clustered together, giving the impression of scattered light gray spots on a dark ground. Scales on tail lighter brown, margined and speckled with black, or not, with dark color predominating proximally and disappearing distally.

Color in life: Color pattern of BPBM 20756 was noted in life as: “Dorsum brown with mid­dorsal row of dark brown chevrons bordered laterally by single row of yellow­brown scales. Venter dark gray with regular series of light gray blotches/flecks, these blotches being elongated on chin and fewer on tail. Under tail charcoal gray. Iris red­orange.” Judging from a color image of this animal, the chevrons are relictual, not extending laterally very far beyond the mid­dorsal region, and are frequently margined with yellow scales behind. An irregular array of tiny yellow spots can be seen over much of the head, body, and limbs. Such dorsal pattern as exists fades distally on the tail, which also gradually assumes a more orange­brown hue than the body

Osteology: The following is based primarily on BPBM 20774, a cleared and doublestained specimen, supplemented by additional notes on similarly cleared and doublestained BPBM 20773 and 20776 and X­rays of BPBM 17707 and 20764. Frontal with a narrow supraorbital waist that is one­third as wide as its posterior margin and narrower than the parietals; supraorbital ridges absent; anterior margin strongly tridentate. Parietals paired, longer than wide. Nasals fused. Premaxillae fused, with 13 teeth loci. Maxillae extend posterior to mid­orbit, each with approximately 25 teeth loci; mandibles each with approximately 30 teeth loci. Quadrate long, narrow, slightly curved. Cranial vault filled with endolymphatic space as far forward as to include the posterior 20% of parietals; solid subtriangular endolymphatic sacs extend from just behind quadrate posteriorly to cover anterior half of suprascapulae and extend dorsally to tops of suprascapulae; ducts to endolymphatic space of cranial vault not obvious. Phalangeal formula 2­3­4­5­3 for manus, 2­3­4­5­4 for pes. Presacral vertebrae 26, three of which are cervical vertebrae lacking ribs; two sacral vertebrae; anteriormost four or five caudal vertebrae with lateral processes.

Hyoid largely cartilage except for ossified first ceratobranchials ( Fig. 4 ). Glossohyal long, extending forward to anterior end of orbits, continuous with basihyal and second ceratobranchials. Hypohyals and first ceratobranchials articulate at posterior end of basihyal. Ceratohyals followed by epihyals, extending posteriorly and dorsally to point just behind squamosal. First ceratobranchial long, tipped by cartilaginous first epibranchial, both extending posteriorly and dorsally to lie along the anterior face of the endolymphatic sacs. Second epibranchial separate from second ceratobranchial, recurved, with distal extremity lying anterior and deep to proximal extremity. Cricoid cartilage single, with lateral ala on each side, a large ventral foramen, a smaller anterodorsal foramen, and a pair of small posterodorsal foramina.

Scapula, coracoids, clavicles, and interclavicle ossified; sternum, epicoracoids, and suprascapulae cartilaginous. Scapula and coracoid separated from each other along approximately half their lengths, each articulating anteriorly with epicoracoid, which extends posteriorly to posterior extremity of coracoid. Ventral and separate from the epicoracoids lies the sternum, which is shield­shaped, with two anterior prongs, and four pairs of costal cartilages attaching along its posterior margin. Ventral to the anterior ends of the epicoracoids are two broad clavicles, each with a large fenestra near the point of articulation with interclavicle and each of which extends dorsolaterally in a long narrow arc to terminate at the base of the respective suprascapula. Interclavicle articulates deep to the clavicles anteriorly, is very narrow anteriorly, but broadens rapidly posteriorly to lie ventral to the epicoracoids.

Ischium wider than long; ischial cartilage extends posterior to ischium for a length greater than length of ischium. BPBM 20776 is a male but I could find no cloacal bones in the specimen. However, those elements do appear as tiny, thin bones in X­rays of BPBM 17707 and 20764.

Var ia t io n: Mensural variation is not great, nor is mensural sexual dimorphism apparent ( Table 2 ). Supralabials to mid­eye are either four or five, and total number of supralabials is either six or seven. No obvious trend in number is evident between the sexes. Number of infralabials varies from five to seven, with five being more common in my sample of females (n = 9/18 = 50% of individuals) than males (n = 2/11 = 18%). Number of lamellae under the fourth toe varies from 11–13 (mean = 11.6) in males and 10–13 (mean = 11.4) in females. In only two males is there a disparity in lamellae number between sides of the same animal as great as two. The large majority of animals have either the same number of lamellae on each fourth toe or only differ by one.

The clearest sexual dimorphism lies in the preanal and femoral pores, which are present in males and lacking in females. Male preanal pore number varies from 14–18 (mean = 16.0) and femoral pore number varies from 4–18 (mean = 7.2), with all except one thigh having no more than nine pores. Femoral pore disparity between thighs of the same animal varies from 1.00 (equal numbers on each thigh) to 2.00 (twice as many on one thigh as on the other). The mean disparity is 1.28.

Color and pattern are virtually identical among animals, with some animals in life showing only a bit more orange­brown wash on the tail than the mode.

Louisiade Archipelago, Papua New Guinea.

Ecology: All individuals were found just inland from the coast at elevations no greater than 40 m and inhabited disturbed forest or gardens in all cases. Animals were collected under rocks, logs, or rotted banana stumps on either moist or dry soil and would scamper into adjacent leaf litter when disturbed. One specimen was found adjacent (<1 m distance) to a stream but most were found away from the immediate vicinity of water. Specimens were not found in closed­canopy rainforest despite more search effort being conducted in that habitat. These geckos often attempted escape by jumping (for admittedly short distances) or wriggling.

To avoid damaging the specimens, no attempt was made to investigate reproductive status of the entire type series. However, two examined males (BPBM 20762, 21692) had swollen testes and epididymes and three females (BPBM 20765, 20772, 21695) had single large eggs occupying most of their posterior abdominal cavities. Hence, reproduction occurs in at least some specimens during April.

Etymology: The name is a combination of the genus name “ Sphaerodactylus ” and the Greek suffix “­odes”, meaning “like”, in reference to the superficial resemblance of the new species to geckos of that American genus.

Range: Known from Sudest, Misima, and Woodlark islands ( Fig. 7 ). Likely to occur on the smaller Louisiades lying between Sudest and Misima, which apparently have yet to be explored by herpetologists.

Remarks: The single known specimen from Woodlark Island (BPBM 17707) differs from the Sudest and Misima specimens in the distribution of its femoral and preanal pores. Most specimens of Nactus sphaerodactylodes have 24–33 preanal­femoral pores arrayed in three clusters, with generally 4–9 pores in each femoral patch. In contrast, the Woodlark specimen has 46 pores, with 14 arrayed in each femoral patch. This is a striking difference and might suggest the presence of a sibling species on Woodlark. However, a single Sudest specimen also has a large number of femoral pores, with 41 pores in total and 9 of these in one femoral patch, with 18 in the other. Hence, the increase in numbers of femoral pores may be an uncommon variant within N. sphaerodactylodes . Given the observed variation in this character within Sudest specimens and the fact that I can find no other feature to distinguish the sole Woodlark specimen from the Sudest and Misima lizards, I assign the Woodlark animal to N. sphaerodactylodes but note that further research might alter that conclusion.

Figures

FIGURE 2. Carination pattern of dorsal scales for holotype of Nactus sphaerodactylodes, BPBM 20764.

FIGURE 3. A) Dorsal, B) lateral, and C) ventral views of head, and D) ventral view of pre­cloacal region showing pores for holotype of Nactus sphaerodactylodes, BPBM 20764.

FIGURE 4. Hyoid of Nactus sphaerodactylodes, BPBM 20774. Clear areas are ossified; lightly stippled areas are partly ossified; heavily stippled areas are cartilaginous. Scale bar is 5 mm.

FIGURE 7. Map of the offshore islands of Milne Bay Province, Papua New Guinea, showing the known locations for Nactus sphaerodactylodes and N. acutus. Closed circle is type locality for N. sphaerodactylodes; open circles are other locations for N. sphaerodactylodes; closed square is type locality for N. acutus.

FIGURE 5. A) Nactus sphaerodactylodes, Sudest Island, photo by G. Shea, and B) Nactus acutus, Rossel Island, photo by F. Kraus, in life, showing distinctive appearance of each.

Tables

TABLE 2. Mensural variation in the type series of Nactus sphaerodactylodes from Sudest Island,

Character	Males (n = 11)	Females (n = 18)
	mean range	mean range
SV (mm)	23.6 21.3–25.4	24.6 20.4–26.0
TrL/SV	0.43 0.42–0.46	0.44 0.39–0.48
CS/SV	0.16 0.15–0.17	0.16 0.15–0.18
TL/SV	0.82 0.65–0.96	0.84 0.68–0.98
TW/SV	0.11 0.10–0.12	0.11 0.10–0.13
HL/SV	0.26 0.25–0.27	0.26 0.25–0.28
HW/SV	0.20 0.19–0.21	0.20 0.18–0.20
HH/SV	0.12 0.11–0.14	0.13 0.10–0.15
FA/ SV	0.13 0.12–0.14	0.13 0.11–0.14
EY/SV	0.051 0.047–0.054	0.050 0.046–0.054
EN/SV	0.078 0.070–0.084	0.077 0.073–0.086
IN/SV	0.043 0.038–0.049	0.043 0.038–0.049
SN/SV	0.11 0.09–0.11	0.11 0.10–0.12
EE/SV	0.091 0.085–0.100	0.093 0.074–0.103
IO/SV	0.072 0.068–0.077	0.074 0.063–0.083
TW/TL	0.14 0.12–0.16	0.13 0.12–0.17
HW/HL	0.75 0.71–0.79	0.75 0.71–0.82
EY/EN	0.65 0.60–0.76	0.65 0.58–0.74
EN/IN	1.8 1.5–2.1	1.8 1.6–2.0
SN/HL	0.40 0.34–0.42	0.41 0.40–0.43
HH/HL	0.47 0.41–0.56	0.49 0.39–0.59