My bad for not being more specific: acanthocephalans (spiny head worms) ARE rotifers (phylum: Rotifera, class: Acanthocephala). Acanths can be barely visible to the naked eye, at least in smaller vertebrates, or in juvenile stages. They are known to get much bigger than microscopic (5-30 cm) which threw me at first, but I think we don't see "successful" parents who get big--they are in the gut, attached firmly. We only see the larva, which are barely visible.
Re: your pics, The little seed like thing was a cyst, aka a "tun"...which is how certain rotifer species encyst or retreat into their shells (lorica) while waiting for improved environmental conditions.
NOTE: acanthocephalans are KNOWN for manipulating their hosts, so any weird neural sensations Might be attributed to the worms. that said, my feeling is that there is pay-back whenever I irritate my morgies/acanths. They cause stinging, biting, nausea, etc. Not entirely sure, but I Think they are actually situating themselves or their close family members along nerves, and/or excreting neurotransmitters /pheromones to cause these sensations. That said, I try to be SUPER cautious when trying poisons (shorthand for: any substance which is intended to eradicate them)...because chasing them might make them go somewhere worse. I dont think I need to tell you, fliaria/cercaria can go to the eyes, brain, etc. so my thought---give them "an out"...a place to escape that won't harm you worse, which might be the gut...maintaining an empty/neutral gut and a low bloodsugar might lure them to escape to gut instead of head/brain, etc. Then a quick flush with epsom or NaCl could get them out Just a thought. No recommendations here...just thoughts and best wishes. Good luck and please keep us posted!