Unusual little creatures-need some guidance

Hello everyone-I was wondering if you all could be of help with something I came across. One of my female guppies got caught in a seashell in my 2.5 gallon aquarium and died. I decided to change the water so my other guppies, shrimp and snails would not be affected. I took out all of my fish, snails and shrimp, and then removed all of the plants. I changed the water, and then put the plants back in with my fish, snails and shrimp. There was water left behind from the plants, and I was about to throw it out when I noticed there are all kinds of creatures in it. Some are wormlike, but they move like catepillars. Then there's are some little white little blob like creatures (about the size and shape of a fish egg) that swim all over the place. There are also some tiny brown creatures that are so small, I can't even see what they look like. I think the worms might be flatworms, but I'm not sure. Two of my shrimp were pregnant last week and no longer have eggs. Could I be mistaking these worms for baby shrimp? Do any of you know what these other creatures might be? Unfortunately, they're so small, I can't even take a picture of them. I had to view most of them through a magnifying glass.