Application of premetamorphic oral cavity electron micrographs for Egyptian toads' taxonomy

Abstract

In the present study, the microanatomy of both the oral disc and buccal cavity of the tadpole of Bufo regularis was described. Tadpoles of 32, 38 and 40 stages were dissected and analyzed using scanning electron microscope. In all the stages, the mouth was ventral and the oral disk width was large, that is, equal to about 44% of the greatest width of the body. The disk was provided with a broad gap on the lower lip; the rest of the mouth was bordered by a large number of papillae. The papillae were arranged in a single row on the dorsolateral part of the mouth; the ventrolateral and ventral lip was surrounded by a double row of papillae. The number of papillae increased with larvae growth, from zero in stage 32 to about 150 in stage 40. The tooth row formula is 2(1)/3(2). The upper and lower beaks were pigmented and serrated. While the upper beak was broadly arched and formed a smooth arc, the lower beak had Vshape. Premetamorphic papillae were observed during the early metamorphic stages, and these degenerated rapidly at about late metamorphic stage. Metamorphic atrophy of the oral structures occurred roughly in the reverse order of development, although the procedure was rapid and more haphazard than the development. We suggested that the oral flaps and the roof papillae play a significant role in the capture of food particles by establishing the inflow of "alimentary water", and aggregating food particles and mucus inside the buccopharyngeal cavity, which may reflect ecological and functional constraints that are relative to the morphology of other suspension feeding anuran larvae. Herein, we described the oral features of the tadpoles of B. regularis.