Leptolalax 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 : 69-71

Leptolalax dringi

Colour in life and preservation (stage 25)

The following description is based on three specimens at Stage 25 with total lengths of 14.4 mm, 31.3 mm and about 56.5 mm ( Table 2 and 3 ). In the larger specimen the distal part of the tail was removed for tissue sampling before preservation in formalin.

The skin is a milky translucent ash grey. The skin of the head and trunk has an intense bluish-white sheen. Head and trunk are pigmented brown, the tail is darker coffee brown. On the dorsal face of the head and trunk, the muscular part of the tail and the dorsal and ventral tail fins, scattered irregularly shaped azure blue iridophores are present ( Fig. 3 C), with those on the tail significantly larger. In lateral view ( Fig. 3 A), the pigmentation of the trunk decreases from dorsal to ventral so that the ventral third of the lateral faces is unpigmented. Around the nares and orbits, unpigmented areas are present. Pigmentation in the smaller specimen is less developed, resulting in a lighter, more transparent appearance. The melanocytes of the muscular part of the tail are assembled to form V-shaped lines along the myosepta of the musculature. The dorsal and ventral fins ( Fig. 3 A) are semitransparent and pigmented with melanocytes. Melanocytes are absent along the outer edges of the fins, with the unpigmented area broader on the ventral fin. In the smaller specimen the caudal fins are unpigmented. In ventral view ( Fig. 3 B), the skin of the head, trunk and tail is unpigmented and translucent with a bluish-white sheen. The red gill tufts, heart, liver, and gut are visible through the skin. Forelimbs are not visible. The gut coil is visible in lateral and ventral views.

After preservation the original brown pigmentation fades ( Fig. 3 G), resulting in pale yellow colouration, the intense bluish-white sheen of the ventral face of the head and trunk disappears. The skin becomes more transparent. Most of the iridophores of the head, trunk, fins and tail are no longer visible.

External morphological features. The body shape is oblong and depressed dorsoventrally ( Fig. 3 A). The dorsal face of the head and body exhibits a longitudinal medial groove where left and right muscle blocks meet. The anterior tip of the head and the snout profile are rounded. The subterminal oral disc protrudes antero-ventrally and is only visible in lateral or ventral view. The nares are round and open anterolaterally. The rim of the nares bears a distinct mid–dorsal projection. The spiracle is sinistral. The cylindrical spiracular tube protrudes from the abdominal wall in its distal part only. The orifice of the spiracle opens postero–laterally and is positioned at 46–47% of the head–trunk length. The tail makes up 73% of the total body length. The eyes are sunken and do not project beyond the body wall, the iris is uniformly black. They are positioned dorsolaterally ( Fig. 3 C) and are not visible in ventral view. The eyes are situated at 20–26% of the distance between the anterior tip of the snout and the trunk–tail junction. The nares are oriented anterolaterally and are closer to the snout than to the eyes. The internarial distance is 66–107% of the interorbital distance ( Table 2 and 3 ).

The dorsal and ventral fins rise slightly at the trunk–tail transition. The dorsal fin is flat/narrow in the proximal third of the tail. The edge of the dorsal fin is straight, while the ventral edge of the ventral fin is slightly convex. The muscular part of the tail makes up 46–54% of the maximum tail height. The upper and lower fins both contribute around 25% of the maximum tail height. The tip of the tail is rounded. The muscles are visible through the transparent skin of the tail. The width of the tail base is 69% of the maximal trunk width. The anal siphon is dextral.

The width of the cup-like oral disc makes up 44–50% of the maximal width of the trunk. The oral disk is anteriorly and posteriorly emarginated along the medial plane. Marginal papillation ( Fig. 3 D and E) is uniserial with a narrow anterior gap. Scattered submargical papillae are present posterior to the mouth. Papillae are short and rounded. The labial ridges bear uniserial rows of narrow, pointed and slightly curved keratodonts. In lateral view, there is a distinct hump on the distal third of the inner side of the keratodonts which separates the curved tip from the wider corpus. The size of the keratodonts decreases in the upper lip from anterior to posterior rows. In the lower lip their size decreases from posterior to anterior. The Labial Tooth Row Formula (LTRF) of the bigger specimen ( Fig. 3 D) is 5(2–5)/3(1–2). In the upper lip keratodont row A-1 is continuous and relatively narrow, four discontinuous rows follow caudally. Rows A-2 and A-3 have a medial divide, resulting in two lateral sections. Rows A-4 and A-5 are divided medially and again laterally, resulting in interrupted rows on both sides of the mouth. In the lower lip, rows P–1 and P–2 are divided medially, P–3 is undivided. The Labial Tooth Row Formula of the smaller specimen ( Fig. 3 E) is 4(2–4)/3(1–2). Rows A-2 to A-4 are only interrupted medially. The dark brown jaw sheaths are well–keratinized and robust. The upper beak lacks a medial notch and has small but sharp serrations. The serration of the lower beak is blunt. The upper jaw sheath is wide and arched. The lower jaw sheath is wide and V-shaped.

Figures

FIGURE 3. Leptolalax dringi. A) Tadpole at Stage 25 in lateral view showing the oblong body shape and protruding oral disks. B) Same individual in dorsal view, note the cylindrical spiracular tube that protrudes from the abdominal wall and opens posterolaterally. C) Same individual in ventral view, note the slender trunk and the sunken eyes. D) Mouth part in ventral view of the bigger specimen (LTRF 5 (2 – 5) / 3 (1 – 3 )). E) Mouthparts in ventral view of the smaller specimen (LTRF 4 (2 – 4) / 3 (1 – 2 )). F) Adult individual. G) Preserved tadpole at Stage 25 in lateral view showing typically faded pigmentation in contrast to living specimens. H) Drawing of tadpole at Stage 25 in lateral view.