Ansonia platysoma

Haas, Alexander, Wolter, Johanna, Hertwig, Stefan T. & Das, Indraneil, 2009, Larval morphologies of three species of stream toads, genus Ansonia (Amphibia: Bufonidae) from East Malaysia (Borneo), with a key to known Bornean Ansonia tadpoles, Zootaxa 2302, pp. 1-18 : 13

Ansonia platysoma

Colour in life ( Fig. 8 ). The background colour of the dorsum is brown with some darkened areas: the roof of the braincase between the eyes and the area dorsal to the vertebral column are densely pigmented. Also a diffuse, dark, broad band stretches from flank to flank forming a saddle. Loosely scattered, small golden pigment cells are found below the eye, on the dorsum, and laterally at the flank-venter transition ( Fig. 8 a). At the level of maximum width the edge of the snout has reduced densities of melanocytes (light areas in Fig. 8 a). The dense pigmentation of the dorsum extends onto the muscular part of the tail and becomes very dense (black) in the distal 40% of the tail ( Fig. 8 c). The ventral side of the tail muscle lacks pigmentation and the vena caudalis ventralis is visible in living specimens. The tail fins and their vascularization are mostly unpigmented, except for the fin edges where dense melanocytes form dark margins ( Fig. 8 c). The iris is black with a clear golden ring around the pupil.

Epidermal melanocytes are small, circular in shape, with irregular fringes. The venter and oral disc are mostly unpigmented and translucent, except for the lateral parts of the abdominal cavity ( Fig. 8 b). The gills and the heart shine through the ventral skin in red; developing front limbs are visible. Some pigmentation is located at the pericard. The gut coils in a spiral that is clearly visible in ventral view ( Fig. 8 b).

The colour in preservation is similar to colouration in life, just lighter. The golden cells of the skin and the golden rim of the iris disappears in preservation.

External morphological features. Ansonia platysoma is a small tadpole. Maximum total length in our sample was 22.10 mm (stage 41; Tab. 2); relative tail length is 64–69%. In dorsal view the body contour is pear shaped with a slight constriction behind the level of the eye ( Fig. 8 b). The body is widest anterior to the eyes, approximately at the level of the nares. The body is clearly dorsoventrally depressed. The snout is greatly expanded bearing a large sucker (oral disc) ventrally. In life, and adhering to the substrate, the snout profile is convex ( Fig. 8 c). The tail fins start in the proximal tail part and increase in height only slightly in the proximal 50% of the tail. Dorsal and ventral tail fins are of similar heights. The fins taper with mild convexity into an acuminate tip. The anal siphon is located medially. The tail musculature is strong and almost as high as the trunk (lateral view) at the trunk-tail junction. In the middle part of the tail, the muscular part significantly tapers and the fins increase in height. The eyes are located dorsally, clearly away from the body contour in dorsal view.

The external nares are much closer to the eyes than to the snout ( Fig. 8 a). The nares have a smooth rim without projections. The interorbital distance is 1.27±0.06 (mean±SD) times the internarinal distance. The spiracle is sinistral and the spiracular orifice is attached to the body wall medially. The spiracle is low on the flank in lateral view when the tadpole is attached to the substrate. The spiracle is directed posterodorsally.

The oral disc is ventral and as wide as the snout in adhesion ( Fig. 7 b). The lower lip of the oral disc bears an uniserial row of marginal papillation; the margin of the upper lip is devoid of free papillae ( Fig. 4 c). The oral disc margin is only mildly indented at the end of the papillae row. Papillae are short, blunt and adjoining. Flat, rounded submarginal papillae are present on the lower lip: The posterior (distal) row is complete (15–16 papillae). A second, anterior submarginal row is reduced to only 1–3 papilla at the far lateral part of the lower lip or is absent. The keratodont rows are uniserial ( Fig. 9 ). The Labial Tooth Row Formula (LTRF) is 2/3. The upper lip keratodont rows caudally reach the level of the lower lip keratodont rows ( Fig. 3 b). Keratodont shape is differentiated according to rows: keratodonts are relatively more finely serrated on the anterior than on the posterior lower lip rows ( Fig. 9 ). The upper beak comprises two short, widely spaced serrated edges; the gap is 2.0–2.6x the length of one beak edge. The lower beak has the shape of a flat V and is serrated along its edge.

Variation. The described pigmentation features did not vary among specimens examined, however, our sample comprised tadpoles of similar mid-larval stages, not excluding ontogenetic variation in colouration. Metric variation is summarized in Tab. 2.

Ecological notes. Ansonia platysoma tadpoles live on rock faces in strong current (presumably high energy) within cascades in mountain streams. Only if disturbed they escape temporarily to areas with moderate currents into pools between the cascades. Thus, when occurring in the same river with A. longidigita , microhabitat choices are clearly distinct between the two species.

Figures

FIGURE 3. Colouration in life of larval Ansonia longidigita (two specimens): (a) dorsal view (stage 26); (b) ventral view (stage 36); (c) lateral view, showing full extend of colouration; note slightly damaged tail tip.

FIGURE 4. External morphology of the three Ansonia species described herein. Each species is shown in lateral (above) and dorsal (below) views and close-up of oral disc (right). Tadpoles were drawn to the same scale to show differences in relative size, however, oral discs not drawn to scale. All scale bars 1 mm. (a) A. longidigita (ZMH A 09368), (b) A. minuta (ZMH A 10003), (c) A. platysoma (ZMH A 10008).

FIGURE 7. SEM images of keratodont rows of Ansonia minuta (ZMH A 10003). Size, shape and serration differentiation of keratodonts varies from row to row. (a) – (e) keratodont rows from anterior to posterior; not to scale.

FIGURE 8. Colouration in life of a Ansonia platysoma tadpole (stage 28). (a) dorsal view; (b) ventral view; (c) lateral view.

FIGURE 9. SEM images of keratodont rows of Ansonia platysoma (ZMH A 10009). Size, shape and serration differentiation of keratodonts varies from row to row. (a) – (d) keratodont rows from anterior to posterior. (a) upper lip rows, (b) – (d) lower lip rows; not to scale.