Well, I spent a long while looking at posts after typing the word 'jellyfish' into the search engine on here and found nothing except that a number of other folks have had them. Little yellow jellyfish with tails - you described them perfectly. It's got to either be a stage or an egg, I'm thinking.
I saw your post to HumaWorm and your mention of candida. I've had a pretty nasty infection since I started their parasite medication. I'm also doing P&B shakes and see a lot of candida in the BMs. It seems like there is candida layered under some of the mucoid plaque. Anyway, having it in my colon doesn't bother me physically - I'm just anxious to get it out. Having it in my vagina was making me nuts, though, physically and mentally. I finally turned to an age-old tradition and made a douche with cider vinegar, water and a squirt of iodine. I followed up a week later, but it has taken away all the evidence of the candida and itching is gone.
Now I got the jellyfish. Cannot find an ID for them anywhere. One reference to them possibly being a water parasite.