Life cycle of Opalina ranarum. 1 Cysts are excreted by the adult frog and orally ingested by a tadpole. 2 After hatching the young gamont migrates to the cloaca. 3, 4 Formation of micro (text with tooltip) Microgametes (sperm) develop from a microgamont in apicomplexans. – and macrogametes ( meiosis (text with tooltip) Meiosis (n.) is a special type of cell division that can only occur in cells with 2 sets or an even number of sets of chromosomes. As in mitosis, meiosis begins when the chromosomes have replicated. However, in meiosis the homologous chromosomes pair and separate during division I. That is followed by a second division in which the chromosome replicates separate (as in mitosis). Because meiosis requires a sequence of divisions, the meiotic products typically come in fours or in tetrads. ). 5 Fusion of the heterogametes. 6 Encystation of the zygote and excretion via feces. 7, 8 After oral uptake of a cyst by another tadpole the trophozoite (text with tooltip) Trophozoite is the feeding stage, usually of a unicellular parasite. grows up in the cloaca (up to 0.5 mm). 8.1, 8.2 The small trophozoite may start division inside the tadpole, finally leading to formation and excretion of cysts (1) which give rise to new trophozoites (2 → 8) after ingestion by another tadpole. 9 When metamorphosis of tadpoles to frogs is completed, the trophozoites (agamonts, trophonts) grow up and form up to 2000 nuclei. 10 During the non-breeding season of the frog the trophozoites multiply by binary fission, the axis of which is either longitudinal or olique-transverse. 11, 12 During the breeding season hormones released by the frog induce rapid divisions of the trophozoites without compensatory nuclear divisions and growth. Thus the parasites (precystic forms) become successively smaller. These stages, finally having 2–12 nuclei, encyst (1), are set free with the feces of the host and become infectious for tadpoles. CI, cilia (text with tooltip) Cilia are eukaryotic flagella that operate by coordinated beats relative to each other. Structurally, cilia and flagella are identical (i.e. 9+2 axoneme from a basal body with associated flagellar roots). Usually cilia are shorter and more numerous than typical flagella. Also, they have an underlying structure of flagellar roots (kineties) that allow for coordination of the flagella. ; CW, cyst wall; N, nucleus

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