Pelobatrachus stejnegeri

Pelobatrachus stejnegeri

have an average total length (TL) from 28.19 mm (stage 25) to 37.14 mm (stage 41); body height (BH) 8.15 mm (stage 25) to 12.02 mm (stage 41); body width (BW) 3.86 mm (stage 25) to 5.83 mm (stage 41); eye diameter (ED) 0.76 mm (stage 25) to 1.54 mm (stage 41); internarial distance is less than the interior, with a measurement that ranges from 1.47 mm (stage 25) to 2.36 mm (stage 41), while lower fin height (LFH), with an average height of 1.06 mm (stage 25) to 1.27 mm, is relatively longer than the upper fin height which only ranges from 0.96 mm to 1.11 mm following the different stages (see Fig. 2 View Fig , Table 1 View Table 1 ).

Notable morphological forms and structures observed include oblong and depressed body shape (BS); dorsolateral eye position (EP) having round pupils; spiracle (SP) sinistral or laevogyrinid having only one spiracle on the left side which protrudes from one-third along its body. Apart from this, the nares (NA) are oval in shape and relatively nearer to their snout and oral disc than the eyes, following a dark brown bar in between; rims of the nares are serrated and depressed in the wall of its body. The vent tube (VT) is medial, found in the ventral centre of its tail muscle connecting to the tadpole’s body, and the dorsal fin (DF) is pointed and low, originating near and at the posterior tip of the dorsal-tail body junction.

Oral disc morphology. The oral apparatus (OA) of the tadpole of Pelobatrachus stejnegeri is a bi-triangular to star-like shaped umbelliform oral disc having an upward-facing oral disc ( Fig. 3 View Fig ). This umbelliform oral disc is located in a subterminal and antero-dorsal position; when it is not fully extended or in preservative, it folds and turns upward into lateral corners medially and the oral disc width (ODW) measures 3.79 to 6.58 mm, eventually becoming smaller at stage 41 (3.32 mm) (see Tables 2–4). This makes the width of the umbelliform oral disc exceed the maximum width of the trunk. The marginal papillae (MP) have slight crenulations or a wavy margin that has at least four rows, when counted medially, of longitudinally oblong submarginal papillae that are present in the lower and upper lips which are regularly positioned and become smaller on the edges or the outermost row. The lower lip is also deeper than its upper lip. There is no disc emargination (DEM) and the labial teeth are absent. The sheath on the upper jaw is serrated, with saw-like projections of various densities of submarginal papillae, and contains a medial notch which is absent in the lower jaw sheath (see Fig. 4 View Fig ).

The oral disc morphology serves many purposes for the tadpoles of Pelobatrachus stejnegeri. This includes the fact that they belong to the neustonic ecomorphological guild (EMG), meaning they are surface feeders. They also have an umbelliform or funnel mouth to harvest necessary particulate matter that serve as food for the tadpole ( Altig & McDiarmid, 2006). The observable oral disc structure makes it a unique species among those in the area. However, this also means Pelobatrachus stejnegeri tadpoles are often overlooked in the different research studies conducted in the Philippines.

Colour in life ( Fig. 5 View Fig ). When observed dorsally, the head and body range from brown, dark brown, light brown to orange brown. They also possess dark brown speckles that increase in density towards the posterior half of the body. Tadpoles were observed to have a dark brown bar that runs from each nare to the anterior edge of the eyes and an obvious pale neuromast. The colour of the oral disc is translucent orange-brown to green with an observable dark brown submarginal papilla. The lower edges of the orange-brown saddle fade to cream and are bordered on the lateral surface by a dark brown band that spans half the length of the tail. There is an area with dense, dark brown flecks where the tail meets the body, which forms a thin line that extends from the body-tail junction and runs along the midline of the lateral tail surface. The dorsal and ventral tail fins are opaque beige brown with a few dark brown speckles, whereas the ventral surface is a transparent cream with mossy jade-like green speckles. The sclera of the eye is wide, black, and flecked with brown-gold. The pupil is black and spherical, while the iris is orange with black specks.

Colour after preservation ( Fig. 6 View Fig ). The body is grey with darker speckles. The oral disc is transparent grey with dark brown submarginal papillae. The dorsal and ventral fins are opaque, pale grey with a few darker speckles; the ventral surface is dark grey and the transparent jade-like green speckles disappear, while the pupils of the eyes turn white.

Microhabitat of tadpoles. The different individuals of Pelobatrachus stejnegeri were found to inhabit both lentic and lotic water systems including puddles, slow-moving waters, and stream banks of secondary forest areas. They are more abundant in superficial water systems that measure 3.81 cm to 63.5 cm. However, they are more abundant in shallower waters, especially in sites 3 and 4 which range from 3.81 cm to 15.24 cm. They are also noted to be more active at night as compared to day, as they are seen more on surface water attaching to debris such as wood, leaves, and rocks at night ( Fig. 7 View Fig ). The tadpoles were found in groups coexisting with other tadpole species including Leptobrachium lumadorum , Limnonectes leytensis , and Pulchrana grandocula .

Microhabitat variables are very important for an organism because they serve as factors for their survival ( Yu et al., 2020). Ecological constraints serve as a means of ascertaining their existence and prevalence in a specific location ( Roff, 1997), despite the influence of evolutionary and historical factors on the widespread distribution of the species, particularly with regard to its substantial impact ( Townsend et al., 2003). Species live in places where physicochemical circumstances are favourable, resources are plentiful, and rivals or predators do not threaten their survival ( Barbaresi et al., 2007).