The Ascetosporea are a group of protists that are parasites of animals, especially marine invertebrates. There are two groups, the haplosporids and paramyxids, which are not particularly similar morphologically but consistently group together on molecular trees, which place them near the base of the Cercozoa. Both produce spores without the complex structures found in similar groups (such as polar filaments or tubules).
Haplosporid spores have a single nucleus and an opening at one end, covered with an internal diaphragm or a distinctive hinged lid. After emerging, it develops within the cells of its host, usually a marine mollusc or annelid, although some infect other groups or freshwater species. The trophic cell is generally multinucleate. Paramyxids develop within the digestive system of marine invertebrates, and undergo internal budding to produce multicellular spores.
- Thomas Cavalier-Smith & Ema E.-Y. Chao (2003). "Phylogeny of Choanozoa, Apusozoa, and other Protozoa and early eukaryote megaevolution". Journal of Molecular Evolution 56 (5): 540–563. doi:10.1007/s00239-002-2424-z. PMID 12698292.
- P. M. Hine, R. B. Carnegie, E. M. Burreson & M. Y. Engelsma (2009). "Inter-relationships of haplosporidians deduced from ultrastructural studies" (PDF). Diseases of Aquatic Organisms 83 (3): 247–256. doi:10.3354/dao02016. PMID 19402456.
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