Latonia nigriventer is a rather inconspicuously coloured, robust frog reaching large sizes of 69.0–128.4 mm in females and 66.6–121.4 mm in males. In the observed individuals, webbing was strongly developed suggesting a substantial aquatic adaptation, and hind limbs were comparatively short. The head was rather flat and the iris heart-shaped. A distinct transversal dermal fold was present in the neck. The colour pattern was similar in all individuals despite differences in distinctness and contrast (Fig. 2). An incomplete mid-dorsal band of the lighter colour was almost always visible in the posterior part of the dorsum. The venter was black to grey with a distinct pattern of white spots which corresponded to raised tubercles in adults. For a detailed morphological description of adults, see Appendix 1; for data and measurements of the holotype, see Appendix 2.
From mid-February until mid-September, i.e. during the presumed breeding season, we observed distinct dark nuptial pads and more or less distinct black, keratinised excrescences on the thorax, ventral part of arms and thighs, plantar surfaces as well as on the outer edge of the webbing in males. In single cases, excrescences were also present on dorsal surface of feet. In females, such structures were distinct only on plantar surfaces and to some degree on the webbing edge, and in very rare cases, single excrescences were seen on the thoracic region (Fig. 5). The excrescences on the body skin had the form of isolated spicules whereas at the webbing edges they formed dense aggregations. The smallest male with clearly developed nuptial pads had a snout-vent length of 66.6 mm, and we therefore used this value as cut-off to distinguish adults from juveniles. Based on specimens > 66 mm, we found no significant difference in the size-weight distribution of males and females (body condition calculated with the relative mass (W r ) condition index; Sztatecsny and Schabetsberger, 2005) using a Mann-Whitney-U test (p = 0.615; N (female/male) = 64/44; Fig. 6), nor did we detect distinct sexual dimorphism in morphometric measurements (Table 2). Slight differences were however seen in foot webbing (see S3 in the Supplement): females had slightly weaker webbing, with a distinct broadening of the toe III webbing usually at the 3rd phalanx, and on toe IV at the 3rd–4th phalanx; whereas in males it usually was seen at the 2nd phalanx at toe III and the 3rd phalanx at toe IV. Forearms were strong in both sexes and could not be reliably used to differentiate females from males (for raw measurements see S4 in the Supplement).
Fig. 6. Latonia nigriventer growth curves including data-driven LOESS (locally weighted scatterplot smoothing; Cleveland and Devlin, 1988) lines and weight gain/loss of recaptured individuals. A) Total captures including recaptures, B) captured individuals excluding recaptures, C) recaptured individuals, D) weight gain (blue) and loss (red) of recaptured females, E) weight gain (blue) and loss (red) of recaptured males as well as weight loss of the single recaptured juvenile (black). Initial capture weight of respective individual given in parentheses.