Fig. 4

Scanning electron microscopy (SEM) images of macrogametocytes and oocyst of E. necatrix. A The complete macrogametocyte is enveloped by a thin layer of plasma membrane on its surface. B A macrogametocyte with a ruptured plasma membrane, with spherical granules, predicted as WFB1s, scattered beneath the membrane. C A ruptured plasma membrane of a macrogametocyte revealed a mulberry-like appearance, exposing numerous WFB1s and PGs on the surface, and the PGs also filled the cytoplasm. D Enlargement of the section displayed in (C) showing WFB1s appearing as spherical dense granules with a relatively smooth surface and approximately 1 μm diameter. E A macrogametocyte with a ruptured plasma membrane, exposing its internal structure. Numerous WFB1s were observed arranged beneath the plasma membrane, with PGs distributed throughout the cytoplasm. Additionally, sponge-like structures were observed inside sectioned organelles within the cytoplasm of the parasite, which were predicted as WFB2. F Enlargement of the section displayed in (E) showing WFB1s 0.8−1.0 μm in diameter. G An intact macrogametocyte, with WFB1s horizontally flattened and fused together on the surface. Gaps and suture structures were observed in the irregular, incompletely formed outer layer. H An intact macrogametocyte, where the outer layer of the oocyst wall has partially formed, and the remaining WFB1s are interconnected on the surface. I An intact oocyst, where the WFB1s finally synthesized the smooth and flat outer oocyst wall. J At the center of the image, a macrogametocyte with a ruptured outer oocyst wall displays cross-linked structures formed by WFB2s. In the lower right corner of the image, an oocyst with a partially stripped outer oocyst wall exposes the inner oocyst wall that has already formed. PG polysaccharide granule, WFB1 wall-forming body 1, WFB2 wall-forming body 2, M membrane, O outer oocyst wall, I inner oocyst wall, OW oocyst wall. Scale bars represent (A, B, C, E, G, H, I, J) 1 μm, (D, F) 200 nm