Rhacophorus penanorum

Haas, Alexander, Hertwig, Stefan T., Krings, Wenke, Braskamp, Enzo, Dehling, Maximilian, Min, Pui Yong, Jankowski, André, Schweizer, Manuel & Das, Indraneil, 2012, Description of three Rhacophorus tadpoles (Lissamphibia: Anura: Rhacophoridae) from Sarawak, Malaysia (Borneo), Zootaxa 3328, pp. 1-19 : 11-14

Rhacophorus penanorum

Colour in life (Stage 31; ZMH A10168 ; Fig. 2 ). The background colour is pale amber with dusting of dark brown melanocytes on the trunk (less dense on the snout) and along the muscular portion of the tail.

Between the eyes, the specimens examined had a patch of pale golden pigment cells covering the braincase and otic region. Other accumulations of pale golden iridocytes are located on the cheek region and upper abdominal region. At the cheek and the posteroventral head region, the internal gills are externally visible as red structures. Two sharply defined round, black spots are present in specimen ZMH A10168 on the dorsal tail fin, and pale spots on the lower fin. The muscular part of the tail is finely mottled with black melanocytes ( Fig. 2 A); the margins of the muscular portion are slightly pronounced by these melanocytes. The edge of the upper fin and the edge of the posterior lower fin are tinted with carrot orange. In the posterior part of the tail, the fin bases are dusted with melanocytes. Myosepta are discernible.

The sclera of the eye is black with scattered golden iridocytes. The iris is densely covered with pale golden iridocytes, visible as a solid golden ring towards the pupil.

The oral disc and sub-buccal region are mostly unpigmented and translucent ( Fig. 2 ). The gills are visible in ventral view as bright red structures. There is a patch of iridocytes ventral to each of the gill baskets. The abdomen and area ventral to the heart are silvery and opaque, the vena abdominalis is visible as a midline streak. The gut coils are not visible.

The vena caudalis ventralis and vena caudalis lateralis are visible in ventral and lateral views, respectively. The ventral side of the muscular part of the tail lacks pigmentation.

The colour in preservation is lighter than in life. All silvery or golden iridocytes become invisible in preservation, thus, rendering the ventral skin translucent; the gut coils become clearly visible and the eyes turn homogeneously black (no golden dust of cells). The carrot orange colour along the tail fin margin disappears in preservation, but conspicuous spots on the tail prevail in preservation.

External morphological features (Stages 26–28, n=9, ZMH A 10168 ). The examined specimens share the following morphological features. Rhacophorus penanorum larvae are of rheophilous, sucker-mouthed type, with streamlined bodies and strongly muscular, elongated tails. They are mid-size tadpoles; the maximum total length in the sample examined was 34.2 mm (Table 2); the tail accounts for 64% (median of sample in Table 2) of the total length. In dorsal view, the body contour is pear shaped, the head broader than the trunk. There is a slight constriction of the contour behind the level of the gill region ( Fig. 2 B). The body is widest posterior to the eyes and dorsoventrally depressed. The snout is greatly expanded, bearing a large sucker (oral disc) ventrally. The snout profile is convex and the tip of the snout moderately rounded in lateral view ( Fig. 2 A). The eyes are located dorsolaterally, set medially from the body contour in dorsal view.

The external nares are at approximately equidistant to the eyes and to the snout and lightly elevated ( Fig. 2 A). The nares are elliptical and face anterolaterally. The rims of the nares are smooth, lacking projections. The spiracle is sinistral, extended into a short tube, the spiracular orifice is free. The spiracle is low on the flank in lateral view (below horizontal mid-trunk line) when the tadpole is attached to the substrate ( Fig. 2 C). The spiracular siphon is directed at a flat angle (almost horizontally) posterodorsally.

The oral disc is ventral and, in adhesion state, is wider than the snout ( Fig. 2 ). A multi-serial row of marginal papillae is present on the lower lip of the oral disc; the papillation along the margin of the upper (anterior) lip has a broad medial gap ( Fig. 2 C, 6). The oral disc margins lacks lateral indentations between upper and lower lip sections. Marginal, distal papillae are fairly long (length> 2x diameter), blunt and adjoining. There is no clear differentiation between marginal and submarginal papillae. Proximal papillae, however, are gradually reduced in length, down to a knob-like shape.

The labial ridges bear uniserial keratodont rows. The Labial Tooth Row Formula (LTRF) ranges from 4(4)/6 to 4(4)/ 7 in the sample examined. If present, row seven on lower lip (P7) is discontinuous; irregular gaps may also be present in row A1 ( Fig. 6 ). Rows A3 and P1 show a slight indentations medially, however, without a clear gap between keratodont-bearing ridges and medial keratodonts. Despite the indentation, we count these as undivided rows in the absence of a clear gap. Upper and lower lip keratodont rows are long, span most of the oral disc, and almost meet in the lateral parts of the oral disc ( Fig. 2 C, 6A). Single keratodonts in the distal rows of upper and lower lip (A1, P4–7), respectively, are substantially smaller than keratodonts in the rows adjacent to the mouth (A2–4, P1–3; Fig. 2 C, 6A). The latter have fine serration that seems to wear off in feeding action ( Fig. 6 D). The edge of the upper beak is of sigmoid shape ( Fig. 6 B), the lower jaw shallow U-shaped. The jaws are strongly developed and keratinized to approximately 80% of the jaw height, and undivided. The edges of the jaw sheaths are coarsely serrated; the serration is blunt ( Fig. 6 B).

The tail musculature is strong and almost as high as the trunk (in lateral view) at the trunk-tail junction and it reduces its height gradually distally. The dorsal tail fin expands at the trunk-tail junction. The dorsal fin is higher than the ventral fin. The tail reaches its maximum height at about mid-tail position. The edges of the fins are shallowly convex in lateral view. The tail fins taper gradually to a moderately rounded tip ( Fig. 2 ). The anal siphon is dextral.

Variation. Little can be said about the natural variation in morphological features in Rhacophorus penanorum tadpoles. The most peripheral lower lip row seem more incomplete in early larval stages than in more advanced tadpoles, and the seventh row on the lower lip was absent in the smallest individual examined. From the size and stages represented in our sample, we conclude that the dot pattern on the tail fins starts with two dots on the upper fin in early stages and increases to three dots on the upper and one dot on the lower fin in more advanced stages. Because R. penanorum larvae are highly specialized rheophiles, their hindlimb development may be altered heterochronically in comparison to other species (Nodzneski & Inger 1990), thus, rendering predictions about maximal size difficult, based on individuals examined and their Gosner stages.

Ecological notes. The tadpoles were found in small shallow stony pools with moderate current, which are connected by steep, narrow channels on bedrock. Within the pools, R. penanorum tadpoles are syntopic with larvae of Leptobrachium sp., Limnonectes kuhlii (Tschudi, 1838) , and Xenophrys dringi (Inger, Stuebing & Tan, 1995) . Further, the tadpole community of this stream comprises Leptobrachella brevicrus Dring, 1983 and Leptolalax dringi Dubois, 1987 larvae, both of which burrow in the gravel of the pool substrate. Ansonia sp. tadpoles were present in sections with faster current in the connecting channels or below water-chutes. Adults of R. penanorum were found in relatively low vegetation (1.5 to 3 m) along the streams. Adult frogs of the following species were detected in the immediate vicinity: Ansonia hanitschi Inger, 1960 , A. torrentis Dring, 1983 , Leptobrachella brevicrus , Leptobrachium sp., Leptolalax dringi , Limnonectes kuhlii , Meristogenys amoropalamus Matsui, 1986 , M. kinabaluensis ( Inger, 1966) , Philautus mjobergi Smith, 1925 , Philautus everetti (Boulenger, 1894) , Staurois tuberilinguis Boulenger, 1918 , and Xenophrys dringi .

Figures

FIGURE 2. Rhacophorus penanorum. A, Stage 31 tadpole in lateral view (ZMH A 10168, 394 Z). Note the black spots and oranges margins of tail fins. B, Same individual in dorsal view, showing colouration features such as the golden iridocyte field between eyes. C, Same specimen, ventral view. The cup-like oral sucker is attached to the glass of the aquarium. The ventral colouration pattern (opaque silvery abdominal pigmentation, medial vena abdominalis / streak visible, bright red gills visible through skin and partly covered by silvery iridocytes) has also been found in other Bornean rheophilous tadpoles within the genus and is not unique to R. penanorum (UNIMAS 8954). D, R. penanorum adult male, day colouration. E. R. penanorum adult male, noctural colour morph.

FIGURE 6. SEM image of Rhacophorus penanorum (ZMH A 10169). A, Overview of oral disc in ventral view; anterior keratodont rows (A 1 – 4) and posterior keratodont rows (P 1 - 6) visible, note that seventh keratodont row on lower lip (P 7) is present only as a small medial stretch of keratodonts and not visible from this perspective; LTRF 4 (4) / 7. B, Close up of the jaw sheaths; orientation as in A; showing details of conspicuously blunt serration on both upper (above) and lower jaws (below). C, Keratodonts of P 3 – P 6 in lateral part of oral disc have possess serration of free margin, however, clefts are shallow. D, On keratodonts of P 1 – P 3 serration is present only on newly formed keratodonts (right), whereas older ones seem to lack serration possibly due to wear.