Über die Entwicklung des marinen parasitischen Phycomyceten Lagenisma coscinodisci (Lagenidiales)

Abstract

This paper concentrates on the study of vegetative development and sexual reproduction in Lagenisma coscinodisci Drebes. Before infecting a diatom cell (Coscinodiscus granii), the freshly released zoospores pass through two different cyst stages. The primary zoospores are kidney-shaped and laterally biflagellated. They form a primary cyst with a spiny cyst wall which is left by isomorphic secondary zoospores. The latter form a secondary cyst (sometimes perhaps repeatedly), which is smooth-walled. The secondary cyst germinates and infects a new diatom cell by means of an infecting tube which enters the cell through the gap between epi- and hypotheca and develops a new thallus. Sexual reproduction is induced by ageing of cultures. Two kinds of isomorphic, kidney-shaped, laterally biflagellated swarmers are produced as in zoosporogenesis. Female-determined swarmers settle down near the host cell and encyst with a more or less smooth wall (oogonia). Male-determined swarmers are obviously attracted by the oogonia and encyst close to them to form a more or less smooth-walled antheridium which drives a thin fertilization tube to the oogonium. During plasmogamy the oogonium develops a thick, short hypha. The cytoplasm with the two nuclei moves completely into this hypha, concentrates near the hyphal tip, and surrounds itself with a thick wall to become a resting spore (oospore) in which karyogamy takes place. The walls of cysts, tubes, hyphae and spores react positively with zinc-chlor-iodide. In the spines and walls of the primary cysts the network of 2 to 3 nm thick fibrils is more distinct than in the other walls. © 1977 Biologischen Anstalt Helgoland.