Henneguya zschokkei is found in fish as an ovoid spore with two anterior polar capsules and two long caudal appendages.[6] Individuals are very small (about 10 micrometers in diameter),[7] but are found aggregated intocysts 3–6 mm in diameter at any place in the animal's musculature.[8]
H. zschokkei is ultimately a highly derivedcnidarian and is distantly related tojellyfish,sea anemones andcorals. However, thisobligate internal parasite so little resembles cnidarians (let alone other multicellular animals) that it, along with many other species in the classMyxosporea, were initially categorized asprotozoa. It is nevertheless most closely related to jellyfish. This species, like most myxosporeans, lacks many of the diagnostic criteria that identify cnidarians. It lacksnervous,epithelial,gut ormuscle cells of any kind.[11]
This parasite has not only lost its mitochondria and themitochondrial DNA residing in them, but also thenuclear genes that code for mitochondrial reproduction.[4]
The origin and cause ofH. zschokkei's highly reduced genome are not yet known. Whileeukaryotes are known for aerobic respiration, a fewunicellular lineages native tohypoxic environments have also lost this capacity. In the absence of oxygen, these single-celled organisms lose the portions of their genome that anticipate andgovern aerobic respiration. These unusual eukaryotes have developedmitochondria-related organelles (MROs) that fulfill many of the functions of conventional mitochondria. However, there is no evidence of an adaptation in the multicellularH. zschokkei.[4]
^ab"Henneguya salminicola".fishpathogens.net. Oregon State University. Oregon Department of Fish and Wildlife.Archived from the original on 2020-02-28. Retrieved2020-02-28.
Fish, Frederic F. (1939). "Observations on Henneguya salminicola Ward, a Myxosporidian Parasitic in Pacific Salmon".The Journal of Parasitology.25 (2):169–172.doi:10.2307/3272359.JSTOR3272359.
Clouthier, Sharon C; Gunning, Derek J; Olafson, Robert W; Kay, William W (December 1997). "Antigenic characterization of Henneguya salminicola".Molecular and Biochemical Parasitology.90 (2):543–548.doi:10.1016/s0166-6851(97)00200-4.PMID9476801.
