New Aspects of Ultrastructural Studies on Gill Filaments and Spiracle Development of Rana Ridibunda Tadpoles
The pattern and sequences of development of the gill apparatus and operculum, in the marsh frog Rana ridibunda via different stages have been analyzed and studied using scanning electron microscopy. The external gills (or transient gills) of the Rana ridibunda tadpole (stage 18) develops as two bulges followed by formation of upper and lower folds (stage 20). The ultrastructural organization of the gill filaments undergoes, conspicuous variations in number and shape. Otherwise, variation in the types density and orientation of epidermal ciliated cells on the gill filaments. The number of filaments is 3+1, 3+2, 5+3, 6+4 and 8+5 at stages 21, 22, 23, 24 and 25 respectively. The shape is either flattened, or finger like –structure. Ciliation are of three types, ciliated cells (CC), microvillated cells (MV) and microridgid "pavement" cells (MR). The new findings in our result are elongted flattened or rounded extensions on epidermal filament surface and transverse cellular bridge connect some microridged cells (MR). Ciliation is few, intermediate, dense or very dense depending on the developmental larval stages. The orientation of the ciliated cells is at right angles or parallel to the long axis of filaments. The external gills are completely hidden from the right to the left side and have largely atrophied followed by formation of internal gills (stages 23-26). The transient gills covered by operculum shifted to the left resulting in an asymmetrical sinistral spiracle that migrated medially, covered with mucus then become empty at premetamorphic stages. Novelty: Noval strctural elements identified during gill development and regression in the marsh frog Rana ridibunda that consist of finger like- protrusions, distributed on the epidermal surface of the secondary gill filaments and located between ciliated and microridged cells. We suggest these are microfilaments rebranched from the secondary filament to increase the respiratory surface areas. Also a cellular bridge observed above the microridged cells of epidermal surface of the gill filaments (Figure 7c arrow heads). Although, Orton categorized anuran, s larvae depending on the spiracular opening of the operculum as anuran tadpoles with spiracle in a median position or in some tadpoles the spiracle in a lateral position (sinistral) others with paired spiracles as pipdae and lepidobatrachus, discoglossideae, bufonidae and microhyla orientalis ranidae and otophryne. While in Rana ridibunda tadpoles of the present study, we found the two positions, firstly a lateral position (sinistral) in early larval stages (Figure 9a-d). Then it migrated into a median spiracle in late stages (Figure 9 e-f). Tadpoles larvae of Rana ridibunda.