Bolitoglossa pygmaea, Bolaños, Federico & Wake, David B., 2009

Bolaños, Federico & Wake, David B., 2009, Two new species of montane web-footed salamanders (Plethodontidae: Bolitoglossa) from the Costa Rica-Panamá border region, Zootaxa 1981, pp. 57-68 : 58-61

Bolitoglossa pygmaea sp. nov.

Pygmy Web-footed Salamander Figure 1

Holotype. UCR 11788, an adult female from Fábrega Massif (coordinates 9°07’00” N, 82°52’40” W) at 3100 m elevation, Provincia de Bocas del Toro, Panamá, collected 1-10 March, 1984 by Luis Diego Gómez.

Paratypes. Twenty-five individuals with the same collecting and locality data as holotype: UCR 17789–11799, MVZ 222490–222503.

Diagnosis. A very small species of Bolitoglossa (subgenus Eladinea) with a short tail and moderately webbed hands and feet that differs from all other species in the genus in its pale coloration and its blackpigmented stomach and peritoneum, which are apparent through the largely depigmented skin. Assigned to Bolitoglossa because it lacks a sublingual fold.

Description. This diminutive species is in the small size-class category for the genus ( Wake & Brame 1972). Standard length ranges from 23.6-32.6 (mean 28.1) in fifteen male paratypes; SL is 23.5-36.8 (mean 29.8) in nine adult females. Tails are short and never exceed standard length; SL divided by tail length ranges from 1.25 to 1.54 in males and from 1.23 to 1.85 in females. The head is relatively broad ( Wake & Brame, 1972); SL divided by head width equals 5.5–6.6 in males and 5.6–6.5 in females. The snout is broadly rounded and of moderate length. Nostrils are large for this genus, although nasolabial protuberances are slight, better developed in males than in females. Eyes are relatively large and prominent and protrude beyond the lateral margins of the head and are visible in ventral view. Teeth are relatively large and well developed, and moderate in number (but relatively numerous in relation to body size). There are 2 or 3 premaxillary teeth (mean 2.1) in males and 3-6 (mean 4) in females. Maxillary teeth number 27–44 (mean 34.6) in males and 18–60 (mean 39) in females. Vomerine teeth number 14–20 (mean 16.3) in males and 15–25 (18.9) in females. Limbs are relatively short; limb interval ranges from 2.0 to 3.0 in males and from 2.5 to 4.5 in females. Hands and feet are relatively large; foot width ranges from 2.1 to 3 (mean 2.6) in males and from 1.9 to 3.5 (mean 2.5) in females. Digits are well differentiated but broadly pointed and more joined basally than webbed ( Fig. 2 A). The first digit of the manus and the first and fifth of the pes are very small. The longer digits of the larger specimens bear small subterminal pads. About one and one-half phalanges of the longest digits are free of the basal digital fusion (which constitutes the webbing in this species). Fingers, in order of decreasing length, are 3-4-2-1; toes are 3-4-2-5-1. Postiliac glands are obscure, but collections of unicellular glands are prominent behind the hind limbs on the lateral sides of the body anterior to the vent.

Measurements (in mm), limb interval and tooth counts of the female holotype. Head width 5.3; snout to gular fold (head length) 8.2; head depth at posterior angle of jaw 3.7; eyelid width 1.2; eyelid length 2.1; anterior rim of orbit to tip of snout 2.0; horizontal orbit diameter 1.7; interorbital distance between angle of eyes 2.9; interorbital distance between eyelids 3.2; snout to forelimb 10.3; distance separating external nares 1.3; snout projection beyond mandible 0.9; shoulder width 3.7; snout to posterior angle of vent (standard length) 33.7; snout to anterior angle of vent 30.5; axilla to groin 18.2; limb interval (number of costal interspaces between adpressed limbs) 2.5; tail length 18.2; tail width at base 1.6; tail depth at base 2.4; forelimb length (to tip of longest finger) 7.4; hind limb length 7.2; hand width 2.4; foot width 2.9; length of fifth toe 0.8; length of third toe 1.1. Numbers of teeth: premaxillary 3; maxillary 27-28; vomerine 10-12.

Coloration of the holotype in alcohol ( Fig. 1 ). Very pale general pigmentation, essentially transparent or translucent. Line of brown pigment from snout along canthus rostralis and through eye (one edge of eyelid) and behind eye in line over each shoulder, where it becomes a diffuse and irregular "line" that extends to the pelvic region. Pigment extends in a pair of weakly defined lines on tail nearly to tip. Scattering of brownish color on top of head, behind eye, and lightly on dorsum, but no evident ground color. Limb insertions, limbs, and hands and feet with lightly scattered brown pigment. Venter almost unpigmented with pale ventrolateral brownish color and some punctate melanophores thinly scattered over ventral surfaces. On the tail venter and behind hind limbs, transparent gland openings stand out as silvery circles. Internal black pigmentation in posterior abdomen and stomach shows through semitransparent ventral and lateral body wall, and heavily pigmented eyeball shows as very dark patch through eyelid. Iris dark brownish-black.

Osteology. The following account is based on radiographs of 12 paratypes, one of which (MVZ 222492) was cleared and stained. Although small, this species has a well developed, well articulated skull. The unpaired premaxilla is small but rather robust and is well articulated to the well-formed maxillary bones. An unpaired dorsal process rises from the dorsum of the tooth-bearing portion of the premaxillary between the enlarged, cartilaginous nasal capsules; at the point where the nasal capsules diverge laterally the process splits into a pair that embraces a relatively large internasal fontanelle. These processes, well articulated to the nasals on their lateral borders, are slender and unexpanded distally. They end about half-way along the length of the fontanelle, where they articulate with the enlarged anterior parts of the frontals. The frontals articulate with each other, and the dorsal fontanelle often found in tropical plethodontids between the frontal and parietal bones is virtually absent. While well formed and relatively large, nasals are not protuberant anteriorly. A small lateral evacuation of the nasals expands internally and marks the passage of the nasolacrimal duct. Septomaxillaries and prefrontals are absent and the nasals form the anterior rim of the orbit. The nasals also articulate with the frontals. No otic crests are present. The operculum lacks a columella but has a minute anteroventral projection that contacts the otic capsule. The preorbital processes of the vomer are long and well developed, and bear teeth nearly to their tips. A large fontanelle separates the bodies of the vomers from each other medially. The 14 trunk vertebrae are well formed and bear bicipital ribs on the first 13. There are two caudosacral vertebrae. Tails are short, and several specimens have lost the tail. Six males have from 22 to 25 (mean 23) caudal vertebrae; two females have 22 and 24 caudal vertebrae. The first caudal vertebra has relatively stout, dorsoventrally expanded, rather short transverse processes that arise at the anterior end of the vertebra and are frontally oriented, but not at an acute angle. The limbs of the cleared and stained individual are in poor condition, but eight mesopodial elements are present in both the manus and pes (distal tarsal 3 is separate from a combined distal tarsal 4+5). Only digit 5 is complete on one limb and it contains two phalanges. The radiographs do not always display phalanges clearly, but when evident the phalangeal formulas are 1-2-3-2 and 1-2-3-3-2. All mesopodials are cartilaginous. No tibial spur is present. The hyoid apparatus is well stained and entirely cartilaginous. The basibranchial is relatively stout (diameter at midpoint about 14% of length) and bears two short cornua at the broad anterior end. No lingual cartilage is present. The first ceratobranchial is extraordinarily slender (diameter 2.5% of length and apparently discontinuous; it is strongly bowed). The second ceratobranchial, in contrast, is short and stout, with a length of about 50% that of the basibranchial and about 75% that of the first ceratobranchial. Its diameter at midpoint is 27% of its length. The epibranchial is elongated and slender, tapering to a pointed tip; it is 2.3 times the length of the basibranchial, 3.4 times the length of the first ceratobranchial, and 4.5 times the length of the second ceratobranchial. The ceratohyals are relatively short and lack a slender anterior extension, and they are relatively narrow. There is no urohyal.

Habitat and range. The species is known only from a small region called the Fábrega Massif, a general plateau with a mean elevation above 3000 m. The main peak, Cerro Fábrega, is 3335 m high (9º 07' N, 82º 53' W) and 3.5 km north of the Costa Rican border on the continental divide (the peak here is Cerro Biné, Fig. 3 ). The plateau is mainly to the north of the peak, and according to the collector the salamanders were found among grass tussocks in an open area.

Etymology. This species name is derived from pygmaeus (L.) and pygmaios (Gr.), in allusion to its miniature size, perhaps the smallest of any member of this large genus.

Figures

FIGURE 1. Dorsal (A) and ventral (B) views of the adult female holotype (UCR 11788) of Bolitoglossa pygmaea, 33.7 mm SL.

FIGURE 2. Dorsal views of the left foot (width 2.9 mm) of the holotype of Bolitoglossa pygmaea (UCR 11788) (A), and of the right foot (width 7.4 mm) of the holotype of Bolitoglossa robinsoni (UCR 11216) (B).

FIGURE 3. The border region between Costa Rica and Panamá showing the six localities from which species described in this paper have been collected. The two species are sympatric on the Fábrega Massif. The 2400 m contour line is indicated. Elevations within this contour are as high as 3335 m.