These are an incidental finding in human stool specimens, and usually indicate that the individual has recently consumed fish such as salmon. Arthur points out that microbiologists should be aware of this finding because of the very real possibility of mistaking these structures as human spermatozoa. This is especially important when dealing with cases of children and suspected sexual abuse. Here is the article that he recommended:
McClelland, R. S., D. M. Murphy, and D. K. Cone. "Report of Spores of Henneguya Salminicola (Myxozoa) in Human Stool Specimens: Possible Source of Confusion with Human Spermatozoa." Journal of Clinical Microbiology 35.11 (1997): 2815-818.
You can differentiate these structures from human spermatozoa by the consistent presence of 2 tail processes (rather than 1 tail in spermatozoa; only occasionally are 2 tails present), larger head structure with 2 polar capsules, and longer tail in relation to the head. Spermatozoa also have a longer defined neck region. Unfortunately, the appearances can be very similar, and therefore getting a dietary history may also be helpful.
Looking at this case after the last, you might ask ‘What is Bobbi doing?’
Pubic lice followed by spermatozoa, does she think this is amusing?
Alas this is only Myxozoa spuriously passed in the stool
After eating parasitized fish caught in a contaminated pool
And so Bobbi can now be absolved of a case that some might be misconstruing