(Cooper et al. 1994 Avian Diseases; SEM of Cochlosoma anatis; Bar = 3um)
It reminds me of diplomonads (eg. Giardia) with its flat shape and adhesive sucker disc appendage - most likely a good adaptation for the intestinal environment. The ventral side is even more diplomonad-esque:
(Cooper et al. 1994 Avian Diseases; SEM of Cochlosoma anatis on intestinal mucosa(dorsal view), note the marks left by the parasite's 'suckers' in the vili; Bar = 5um)
Also, both are 'amitochondriate' anaerobes; trichomonads (and all the other parabasalians) have hydrogenosomes, which are ultra-reduced mitochondria with a pathway for producing hydrogen gas. Diplomonads and retortamonads lack hydrogenosomes, and have really taken the whole Mitochondria Lite business to the extreme - they have tiny non-descript mitosomes which are basically kept around for one metabolic purpose: FeS cluster metabolism*.
I digress, but that's pretty much all I have to say about Cochlosoma. Besides its peculiar shape, it seems to be your garden variety trichomonad with a case of Giardia-envy. Although who knows, these things are also grotesquely understudied...
Brace yourselves for the next mystery micrograph, which shall be posted
*Thus far no eukaryote has been found without at least that part of the mitochondrial metabolic pathways left behind. Kreb's/TCA cycle can be quite 'easily' dispensed with or greatly reduced, despite it being the more 'famous' part of mitochondrial metabolism. Microsporidia (intracellular parasitic fungi) have the most reduced mitochondria. Turns out that their mitochondria lack ATP production altogether. The ATP is stolen from the host cell, and actually imported to the mitochondrion! (Tsaousis et al. Nature 2008)
Cooper, G., Shivaprasad, H., Bickford, A., Nordhausen, R., Munn, R., & Jeffrey, J. (1995). Enteritis in Turkeys Associated with an Unusual Flagellated Protozoan (Cochlosoma anatis) Avian Diseases, 39 (1) DOI: 10.2307/1592001
Hampl, V. (2006). Affiliation of Cochlosoma to trichomonads confirmed by phylogenetic analysis of the small-subunit rRNA gene and a new family concept of the order Trichomonadida INTERNATIONAL JOURNAL OF SYSTEMATIC AND EVOLUTIONARY MICROBIOLOGY, 56 (1), 305-312 DOI: 10.1099/ijs.0.63754-0
Tsaousis, A., Kunji, E., Goldberg, A., Lucocq, J., Hirt, R., & Embley, T. (2008). A novel route for ATP acquisition by the remnant mitochondria of Encephalitozoon cuniculi Nature, 453 (7194), 553-556 DOI: 10.1038/nature06903