If I had to guess, I'd guess either:
they are young bamboo shrimp that have some weird coloration from whatever region they come from, and haven't grown out their fans yet. They're slow growers.
or
they're something related to a green lace shrimp. The smaller fans look very much like those on the green lace shrimp I keep, and they're shaped similarly as well, and fit the size profile... larger than a cherry, smaller than a bamboo, around the size of an adult amano.