Myxosoma funduli Kudo (Myxosporida) in Fundulus kansae: Ultrastructure of the Plasmodium Wall and of Sporogenesis*

Abstract

SYNOPSIS Ultrastructure of the plasmodium wall and of sporogenesis were studied in Myxosoma funduli Kudo infecting the gills of Fundulus kansae (Garman). Plasmodia were located within the lamellar tissues adjacent to sinuses and capillaries. The plasmodium wall consisted of a single unit membrane which was continuous with numerous pinocytic canals extending into the parasite ectoplasm. The plasmodium membrane was covered by a surface coat of almost uniform thickness which prevented direct parasite‐host cell contact. Numerous generative cells and cell aggregates, representing early stages of spore development, were seen in immature plasmodia. Later stages of spore development, including mature spores, were observed in older plasmodia. Sporogenesis was initiated by envelopment of one generative cell, the sporont, by a 2nd, nondividing cell, the envelope cell. The sporont and its progeny proceeded through a series of divisions until there were 10 cells, all compartmentalized within the envelope cell. Subsequently, the 10 cells became structurally differentiated and arranged into two 5‐celled spore‐producing units, each consisting of 1 binucleate sporoplasm and 2 capsulogenic cells, all surrounded by 2 valvogenic cells. Observations of later developmental stages revealed the major events of capsulogenesis, valvogenesis, and sporoplasm maturation, which occurred concomitantly during spore construction.

Development of the PKX myxosporean in rainbow trout Salmo gairdneri

“…Polar capsule formation in PKX indicated spore formation. However, trophozoites were more numerous than spores, even late in the infection, as Bond (1938) reported for Sphaerospora r e n d s in the killifish Fundulus heteroclitus L. Polar capsules may form before valvogenesis occurs, as in other myxosporeans (Desser & Paterson 1978, Current et al 1979, and valves were not apparent in the PKX spore. The spores remained within their pseudoplasmodium throughout the infections, and this, combined with the apparent lack of valves, indicates that the spores were not fully developed.…”

“…Of the myxosporeans examined by transmission electron microscopy, most form electron-dense cytoplasmic inclusions, similar to haplosporosomes in the Ascetospora (Current & Janovy 1977, Desser & Paterson 1978, Current et al 1979, Lorn et al 1982, Desser et al 1983, and organisms of both phyla reproduce by internal cleavage (endogenous budding).…”

“…However, internal cleavage and organelles similar to haplosporosomes also occur among members of the Myxozoa (Current & Janovy 1977, Desser and Paterson 1978, Current et al 1979, Lom et al 1982. Desser et al 1983, and Ferguson & Needham (1978) and Seagrave e t al.…”

Ultrastructural data on the spore of Myxobolus maculatus n. sp. (phylum Myxozoa), parasite from the Amazonian fish Metynnis maculatus (Teleostei)

“…Comparison of the plasmodium wall and sporogenesis of the cycle life stages of this species to those of other Myxobolus spp. also revealed morphologic and ultrastructural similarities (Lom & Puytorac 1965, Desser & Paterson 1978, Current et al 1979, Lom & Dyková 1992.…”

Light and electron microscopic studies on Myxobolus egyptica sp. nov. (Myxozoa, Myxosporea), infecting the hornlip mullet Oedalechilus labiosus from the Red Sea

“…The typical flat valve cell with its flat nucleus was observed during the present valvogenesis. In mature spores, electron dense bodies were noticed in the cytoplasm of the valvogenic cells of the present species, these bodies are thought to be precursor materials for valve wall formation (Current et al 1979, Stehr 1986, El-Matbouli et al 1990). …”