Microsporidia - Morphology

Morphology

Microsporidia lack mitochondria and possess, instead, mitosomes. They also lack motile structures such as flagella.
Microsporidia produce highly resistant spores to survive outside the host for up to several years. Spore morphology is useful in distinguishing between different species. Spores of most species are oval or pyriform, but rod-shaped or spherical spores are not unusual. A few genera produce spores of unique shape for the genus.

The spore is protected by a wall, consisting of three layers:

• an outer electron-dense exospore
• a median, wide and seemingly structureless endospore, containing chitin
• a thin internal plasma membrane

In most cases there are two closely associated nuclei, forming a diplokaryon, but sometimes there is only one.
The anterior half of the spore contains a harpoon-like apparatus with a long thread-like polar filament, which is coiled up in the posterior half of the spore. The anterior part of the polar filament is surrounded by a polaroplast, a lamella of membranes. Behind the polar filament there is a posterior vacuole.