Ultrastructural features of <i>Amoeboaphelidium protococcarum</i> parasitizing <i>Scenedesmus dimorphus</i>.

<p><b>A</b>. A healthy, uninfected <i>S. dimorphus</i> cell, surrounded by a cell wall (HCW) and containing lipid globules (L), starch granules (S), a nucleus (N), and a pyrenoid (Py). <b>B</b>. Three motile aplanospores; aplanospores have multiple filose pseudopodia (FP) and contain a single nucleus, multiple lipid globules backed by endoplasmic reticulum (ER), microbodies (Mb), multiple mitochondria (M), a Golgi apparatus (G), and dispersed ribosomes (R). <b>C</b>. Mitochondrion, illustrating lamellar cristae. <b>D</b>. Microbody (Mb) (arrow) appressed to two lipid globules. <b>E</b>. Multi-layered endoplasmic reticulum (arrow) backing microbody in the microbody-lipid globule complex. <b>F</b>. Golgi apparatus. <b>G</b>. Motile aplanospore with pseudopodium. <b>H</b>. Magnification of pseudopodium in G; putative actin microfilaments indicated by arrows. <b>I-K</b>. Aplanospore cysts. <b>I</b>. Cyst containing a nucleus and lipid globule, and subtended by an appressorium (Apr). <b>J</b>. Cyst penetrating host cell wall with a penetration tube. <b>K</b>. An aplanospore cyst surrounded by a rigid cell wall (CCW) and containing a vacuole (Vac) and a multivesicular body (Mvb); the penetration tube penetrates the host cell wall; regions indicated by single and double arrows are magnified in Figs. 3L and M. <b>L, M</b>. Single arrow (L) and double arrows (M) illustrate continuity of parasite plasma membrane around parasite protoplasm as cyst contents are injected into host (Fig. 3K). Bars: H = .025 µm; C, F, L, M = 0.1 µm; D, E = 0.25 µm; B, G, I, J = 0.5 µm; A, K = 1.0 µm.