Heterixalus tricolor (Blommers-Schlosser, 1982)

Griep, Stine & Glos, Julian, 2020, Description of tadpoles of the frogs Heterixalus tricolor, H. carbonei and H luteostriatus (Anura: Hyperoliidae) from western Madagascar, Zootaxa 4767 (2), pp. 332-344 : 337-338

Heterixalus tricolor

The description of external morphology is based on a specimen in stage 30, field number 56#25, from Kirindy Forest (TL 23.23 mm, BL 8.14 mm; Tables 1-2 , Fig. 1 ).

External morphology. In the dorsal view, the body form is ovoid. Its widest point lies in the distal half to three-quarters of the body. The snout is broadly rounded. In profile, the body is slightly depressed (BW 110% of BH). Its maximal height is in its distal half shortly behind mid-body. The snout is pointed. The eyes are moderately sized (ED 14% of BL). Their position is lateral with a dorsolateral orientation, visible in the ventral view. Nares are located dorsolaterally, nearer to the snout than to the eyes. They have a dark spot on their back and open both dorso- and anterolaterally. Their opening form is round. The distance between nostrils is about one third of the distance between orbitals (NN 35% of IOD). The spiracle is sinistral and visible in the dorsal view. Its opening is located at maximum body width, shortly below the level of the proximal end of the tail myotomes axis. Its inner wall is free from the body, formed in a way that the aperture opens more laterally than posterodorsally. The vent tube is dextral, very short, and not attached to the ventral fin. The coiled gut is visible. The tail is nearly twice as long as the body (TAL 185% of BL). The tail muscle is narrow (TMW 34% of BW) and low (TMH 41% of BH, TMHM 32% of THM). At the highest point, which lies in its proximal quarter to half, the tail is nearly as high as the body (MTH 87% of BH). From that point, the tail height continuously lowers towards the pointed tail tip (THM 77% of MTH), which is reached by the tail muscle. The dorsal fin originates proximal to the body tail junction. The fin is pointed in its origin and widens towards the point of maximum tail height. From that point, dorsal fin height remains mostly constant until it starts lowering in the distal half of the tail towards the fin’s pointed end at the tail tip. The ventral fin originates at the body tail junction. It reaches its maximum height, which is lower than the maximum height of the dorsal fin, in the proximal quarter of the tail. The height remains mostly constant until it starts lowering in the distal half of the tail towards the fin’s pointed tail tip.

The oral disc is small (ODW32% of BW), and its type is generalized without emargination. Its position and orientation are anteroventral. Ventrally and laterally, on the lower labium, there is a single row of very few marginal papillae and some submarginal papillae. The papillae are rounded and form a moderately sized dorsal gap (DG 47% of ODW). On the upper labium, the labial teeth form one long row (A1 is 64% of ODW). The LTRF is 1/3(1), P3 is much shorter than P1 and P2. Labial teeth have three to four cusps. The jaws sheaths are wide (JL 54% of ODW) with pointed serrations at the edges. Jaws sheaths are half keratinized. The upper jaw sheath is arched, the lower one is V-shaped. Closed, the upper jaw sheath covers the lower one.

Coloration in preservative. The body of the tadpole is pigmented dorsally and on the anterior part of the sides. The pigmentation is most prominent around the lower halves of the eyes. There is hardly any pigmentation at the abdomen and on the lower, distal sides of the body. The coiled gut is visible. Pigmentation is weak on the spiracle and nonexistent on the limb buds. The eyes are black. The dorsal fin and the tail muscle have only sparse pigmentation. The ventral fin is mostly without pigmentation. There is a dark brown line on parts of the tail myotomes axis. The oral disc has no pigments except for the dark brown keratinized parts of the jaws sheaths and the labial teeth.

Variation. The external morphology and general appearance was very similar between specimens. The ratios taken on five tadpoles in stages 30 to 35 vary in the following proportions: BH 108-118% of BW; ED 14-15% of BL; NN 26-37% of IOD; TAL 176-188% of BL; TMW 25-34% of BW; TMH 37-42% of BH; TMHM 25-32% of THM; THM 77-90% of MTH; MTH 80-91% of BH; DF 87-162% of TMHM; VF 122-135% of TMHM; DF 67- 125% of VF; ODW 28-32% of BW; DG 45-57% of ODW; A1 62-69% of ODW; JL 52-60% of ODW.

Figures

FIGURE 1. Tadpole of Heterixalus tricolor in (A) the lateral and (B) the dorsal view, its oral disc (C) under the scanning electron microscope, (D) labial teeth from P1.