Development and ultrastructure of the marine, parasitic oomycete, Lagenisma coscinodisci (Lagenidiales): encystment of primary zoospores

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Abstract
The primary zoospores of Lagenisma contain many peripheral encystment vesicles. They disappear when the primary cyst wall is formed. The primary cyst wall consists of a 6 nm thick, electron-dense layer and is secreted in less than 1 s. Ten seconds later, the flagella are retracted in the straight-in way within 3-4 s. The cyst bears spines which initially are filled with cytoplasm. They do not seem to contain cytoskeletal elements and possibly are shaped by a locally restricted extension of the cytoplasm and the cyst wall when the latter is formed. Later on, a secondary, inner, thicker fibrillar cyst wall layer is secreted. In contrast with other developmental stages studied hitherto, the vegetative primary cyst contains microbody-like structures.