Minchinia mercenariae (Haplosporidian) from the clam Mercenaria mercenaria; 13 - SEM of spore with arrow pointing to the opening; 12 - spore with a closed hinged lid; 2 - Minchinia's 'habitat' in the clam connective tissue (which it has taken over), while the digestive epithelia (DE) remain untouched. (Ford et al. 2009 JEM)
Haplosporidia are unicellular parasites known for their peculiar jug-with-a-lid spores. Presumably those spores get inside the host and the hinged lid opens (cute!), releasing the organism, but I was unable to find any details of their invasion process. After finding their way inside the host and excysting, they exist in an amoeboid stage for a while, perhaps to quickly spread throughout the host. They then proceed to form multinuclear plasmodia inside host tissues and form spores via palintomy (cellularisation) (kinda like apicomplexans and some dinos), and release the spores.
Many of them are commercially important due to their taste in shellfish. However, they seem to linger in obscurity despire that fact. In fact, one wonders whether their complete life cycles are known yet. Parasites are notorious for spanning multiple species at times, and it's hard to rule out a secondary host of some sort. However, the presence of what seems to be a complete set of life cycle stages within one sample suggest a single host at the moment, but intermediates remain possible (Azavedo et al. 2008 J Parasitol).
TEM of Haplosporidium lusitanicum; Nu - nucleus; Sp - 'spherule' (multivesicular body) Hp - haplosporosome; Op - operculum ('lid'). Right: drawing of H.montforti; w- spore wall, F - filament (Left: Azevedo 1984 J Parasitol; Right: Azavedo et al. 2006 J Invert Pathol)
There are three major genera of Haplosporidia, which are quite distinct morphologically. See this nice page describing them, with pictures (thanks, Johan!). They used to be categorised based on spore ornamentation, but that turned out to be rather messy. Haplosporidia reside in Rhizaria (TC-S & Chao 2002), close to Cercozoa, as shown in the aforementioned website and in the Pawlowski & Burki 2009 tree. Rhizarians have gote so much cool stuff it ain't funny.
Next up we will have a glimpse of Paramyxids, which seem to be related to today's topic. They also have really interesting lifestyles. TC-S and Chao (2002, 2003) place them in "Ascetosporea" (Sprague 1979), sister to Haplosporidians, and Pawlowski (2008) doesn't seem to mind, so that's enough excuse to talk about them. I mean, I just READ a few paragraphs of TC-S, we can't let that effort go to waste! Besides, not like a little bit of long branch attraction has ever harmed anyone...
But that'll be later this week. I shouldn't really be reviewing Rhizaria right now or anything, even though that would be kinda fun!
Azevedo, C. (1984). Ultrastructure of the Spore of Haplosporidium lusitanicum sp. n. (Haplosporida, Haplosporidiidae), Parasite of a Marine Mollusc The Journal of Parasitology, 70 (3) DOI: 10.2307/3281564
AZEVEDO, C., BALSEIRO, P., CASAL, G., GESTAL, C., ARANGUREN, R., STOKES, N., CARNEGIE, R., NOVOA, B., BURRESON, E., & FIGUERAS, A. (2006). Ultrastructural and molecular characterization of Haplosporidium montforti n. sp., parasite of the European abalone Haliotis tuberculata Journal of Invertebrate Pathology, 92 (1), 23-32 DOI: 10.1016/j.jip.2006.02.002
Azevedo, C., Casal, G., & Montes, J. (2008). Ultrastructural Developmental Cycle of Haplosporidium montforti (Phylum Haplosporidia) in its Farmed Abalone Host, Haliotis tuberculata (Gastropoda) Journal of Parasitology, 94 (1), 137-142 DOI: 10.1645/GE-1177.1
Cavalier-Smith, T., & Chao, E. (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
FORD, S., STOKES, N., BURRESON, E., SCARPA, E., CARNEGIE, R., KRAEUTER, J., & BUSHEK, D. (2009). Minchinia mercenariae n. sp. (Haplosporidia) in the Hard Clam
Mercenaria mercenaria Implications of a Rare Parasite in a Commercially Important Host
Journal of Eukaryotic Microbiology, 56 (6), 542-551 DOI: 10.1111/j.1550-7408.2009.00432.x