ABSTRACT. The ultrastructural features of sporogony of Goussia carpelli (Leger & Stankovich) are described from the intestine of laboratory-infected carp. Zygotes were encased by a bilayered membrane (about 4 5 nm thick), which could be taken for the outer cell boundary of the oocyst. No indications were found that the parasitophorous vacuole membrane of the host cell contributed to oocyst wall formation. The formation of 4 sporoblasts from the sporont appeared to occur simultaneously. Initially, the sporoblasts were enveloped by a unit membrane and later were covered by a fine bilayered envelope which then transformed into a 120 nm thick sporocyst wall. The sporocyst wall formed a bivalved shell; the valves were joined by a continuous suture visible in the scanning electron microscope as a slightly prominent longitudinal fold. The sporozoites started to develop at opposite sides of the residual body within the sporoblasts, and in more advanced stages 2 sporozoites lying side by side could be observed. The sporozoites were morphologically similar to sporozoites of other Coccidia. During sporulation, the host cell lost its integrity, detenorated and turned to an almost structureless mass whlch appeared as the 'yellow bodies' known from light microscopy.
Examination of samples of three-spined sticklebacks Gasterosteus aculeatus from Loch Flemington in Scotland and from 3 sites in southern England revealed hitherto unknown myxosporean stages in the choroidal rete mirabile of the eye. This paper describes the light and ultrastructural features of these stages and discusses affinities with PKX and extrasporogonic stages of other myxosporean paras~tes, particularly those belonging to the genus Sphaerospora.O Inter-Research/Printed in Germany
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