Figure 4

TEM of sporogonial stages of Desmozoon lepeophtherii n. gen., n. sp. a) An early divisional sporont with tubules in the host cell cytoplasm has a modest thickening of the plasma membrane (white arrows) and precocious development of the pf (black arrows) associated with the nucleus and cytoplasmic cisternae (white asterisks) that start to form the pf bundles. b) Sporont with a thickening plasma membrane (white arrows), a diffuse nucleus showing signs of recent activity (black arrows), the developing ad (black asterisks) is associated with a nuclear invagination, from which the developing pf extends. Tubules are present in the host cell cytoplasm. c) Immature sporoblasts have a more defined nucleus and show signs of pf organisation in to bundles (black arrows), which are arranged in close proximity to large ELIs (black asterisks), tubules are still present in the host cell cytoplasm. d) Maturing sporoblasts have features of mature spores such as a pp and a more mature pf. ELIs (black asterisks) have dark granules associated with the membranes (white arrows). e) Some sporoblasts at an equivalent developmental stage to (d) have two sets of pf apparatus (white/black asterisks) both with associated ELIs. f) An early spore with a fully formed exospore layer (black arrows) and a developing endospore layer (white arrows). This late stage shows a typical internal arrangement seen in mature spores; ad and pp are located at the anterior of the spore, the single nucleus and rows of pf (white asterisks) are medially positioned, ELIs (black asterisks) are posteriorly located and will form part of the posterior vacuole. A secretion from the exospore forms a fragile interfacial envelope which creates a void surrounding the spore (open black arrows). All scale bars 1 μm. ad (anchoring disc); n (nucleus); pf (polar filament); pp (polaroplast); t (tubules).