They may have hatched for some reason but will die as well. Look at amano shrimp, they will hatch in freshwater and you can see the zoa's in the water, but they have to be moved to saltwater quickly after hatching or they won't make it.
20g platy, , 2 x 10g shrimp, 3 x 20g shrimp, 7.5g shrimp and 1 great dane/mastiff puppy.
Sump Pimp #2
My Tanks and my shrimps