Megophrys dringi

Oberhummer, Evelyne, Barten, Catherin, Schweizer, Manuel, Das, Indraneil, Haas, Alexander & Hertwig, Stefan T., 2014, Description of the tadpoles of three rare species of megophryid frogs (Amphibia: Anura: Megophryidae) from Gunung Mulu, Sarawak, Malaysia, Zootaxa 3835 (1), pp. 59-79 : 71-73

Megophrys dringi

Colour in life and preservation (stage 25)

The following description is based on four specimens at Stage 25 with maximum total lengths ranging from 23.3 to 37.6 mm ( Table 2 and 3 ).

The background colour of the body and tail of living specimens is semi-transparent grey (slightly lighter at the snout). The dorsal and lateral faces of the body and tail show a conspicuous pattern of intense dark brown and gold pigmentation ( Fig. 4 A and B). The dorsal face of the head and trunk are covered by a shiny golden pigmentation that reaches laterally to below the eye. Two diffuse bands of dark brown melanocytes are present dorsolaterally ( Fig. 4 C). Between the anterior edges of the eyes and the medial point of the upper lip a distinct, broadly V-shaped pattern consisting of small dark brown melanocytes is visible. The lateral tips of the lips show tiny golden irdiophores. The lips are light beige. The submarginal papillation of the oral disc is dark brown. The sclera of the eye is black with a light green line postero-dorsal to the pupil. The iris is dark golden yellow to orange sprinkled with black dots, comparable to the iris colouration in adults. The pupil is homogenously black and rounded. The spiraculum is translucent and unpigmented.

The dorsal face of the anterior part of the tail is covered by a marbled pattern of gold and brown pigmentation ( Fig. 4 C). On the posterior part of the tail, isolated, irregularly shaped spots formed by pale golden iridophores on the rich dark brown pigmentation are present. Laterally ( Fig. 4 A), the tail is pigmented dark brown, interspersed with pale golden iridophores which form short stripes on the anterior half of the tail and irregularly shaped spots on the posterior half. The fins are milky translucent. The anterior third of the dorsal fin exhibits golden pigmentation marbled with a pattern of dark brown melanocytes. The proximal half of the ventral fin is unpigmented, the rest of the fins exhibit diffuse brown pigmentation interspersed either with irregularly shaped spots formed by pale golden iridophores or with isolated iridophores of the same colour. In ventral view ( Fig. 4 B), the head, trunk and tail are milky translucent with a few irregularly shaped spots made up of pale golden iridophores. The gills and gut coils are visible in lateral and ventral view through the transparent skin.

In preserved specimens ( Fig. 4 F), the dark patterns fade and the skin turns transparent. The golden pigmentation of the dorsal face of the head and trunk becomes pale whitish, and the brown V-shaped pattern disappears. The tail muscles appear light cyan. The gut is visible. The iris is black, and the pupil dark grey ( Fig. 4 E).

External morphological features. The head and trunk are elongate ovoid ( Fig. 4 C). The head is only slightly broader than the trunk. The terminal oral disk is large and points upwards. The eyes are situated dorsolaterally, 29–37% of the distance between the anterior tip of the snout and the trunk-tail junction ( Table 2 and 3 ). The pupils are round. The dorsolateral nares are closer to the eyes than to the snout and situated 67% of the distance between the anterior tip of the snout and the eyes. The internarial distance ( IND) is 78% of the interorbital distance (IOD). The oval nares open laterally. The rims of the nares are slightly raised from the body wall and exhibit a short middorsal projection. The spiracle is sinistral and extends to a short siphon with a free round spiracular orifice. The opening of the spiracle is situated at 47–61% of the head trunk length and below the horizontal mid trunk line. The spiracular siphon is directed postero-dorsally at an angle of 45 relative to the horizontal line of the body ( Fig. 4 A). The tail accounts for 70% of overall body length ( Fig. 4 A). The dorsal fin inserts a short distance behind the trunktail junction. The ventral fin is connected to the trunk. The anal siphon opens medially. The dorsal edge of the fin is straight and the muscular tail makes up 71–85% of body depth. The width of the base of the tail is 58–63% of the maximal trunk width.

The mouth labia of the dorso-terminal, umbelliform oral disc form a surface-oriented funnel whose lateral corners point upwards when not fully extended ( Fig. 4 E). In preserved specimens, the width of the oral disc is 75–78% of the maximal width of the trunk. Marginal papillae are absent and the edges of the lips are smooth. The upper and lower lips bear numerous low, rounded or slightly elongated submarginal papillae. The lower lip is deeper than the upper lip and bears about four irregular rows of submarginal papillae formed by irregularly positioned tubercles. The first row is situated directly centripedal to the margin of the oral disc. A few finger-like papillae are present on both sides of the mouth-orifice. The submarginal papillae on the upper lip are smaller than those on the lower lip, and round. Submarginal papillae are pigmented brown contrast starkly with the light background colour of the lips, particularly in larger specimens ( Fig. 4 E). Keratodonts are absent. The jaw sheaths are thin, weakly keratinised and finely serrated. Both jaw sheaths are unpigmented except for a band of brown. The upper jaw sheath displays a median notch. The lower jaw sheath is thin and sickle-shaped.

Figures

FIGURE 4. Megophrys dringi. A) Tadpole at stage 25 in lateral view, golden pigment on the head, brown pigment on fin and in front of the eyes. B) Same individual in ventral view, only a small amount of pigmentation remains. C) Same individual in dorsal view, the tail is patterned golden / brown. D) Adult individual. E) Overview of the oral disc of Megophrys dringi in preservation at Stage 25. Numerous submarginal papillae are found directly below the lips. F) Preserved tadpole at Stage 25 in lateral view showing typically faded pigmentation in contrast to living specimens. G) Drawing of tadpole at Stage 25 in lateral view.