Scanning electron microscopic observation of ultrastructure of Dirofilaria immitis microfilaria.

Ultrastructure of Dirofilaria immitis microfilaria(Mf) was imaged through scanning and transmission electron microscopies. Transverse annular striations covered all over the surface of the whole body. Two small pores on the cephalic disk and the mouth-like cavity at a ventral side of the first striation next to the cephalic disk were observed. A single triangular hook was projected from the upper palate. The excretory pore was observed at the 80th annulus from the anterior end, and the anal pore at the 90th annulus from the posterior end. The both pores were located at the ventral side of the body. This study first demonstrated that a large number of nuclear column cells were distributed in the body cavity. These cells were spherical and about 1 microm in diameter. Each of the cells contained a spherical nucleus and was connected to each other by micro-strings that were running radially. Many flattened muscle cells were located at the inside of the hypodermis of the whole body. The tail contained only a single longitudinal muscle cell.