Parasitic dinoflagellates and ellobiopsids (Ellobiopsidae) or Cladogonium ogishimae
I will refer to both here as there is little studies on these parasites and a general lack of evidence of both types of parasites. Plus a lot of people have been calling this ellobiopsidae for many years.
What we deal with in freshwater shrimp is more likely Cladogonium ogishimae, rather than ellobiopsidae.
The reason Cladogonium ogishimae fits better is because it: Infects freshwater shrimp, found on the shrimp's pleopods, and turns green eventually.
Ellobiopsidae, of which there are thousands of species and many of them are parasitic. Dinoflagellates and ellobiopsids are major parasites in marine invertebrates and fishes. Ellobiopsidae seem to appear on the tops of shrimps, rather than on the pleopods.
The possible treatments for both will remain the same.
These parasites invade the host's eggs, digestive tract, soft tissue and blood of the organism, who eventually, succumbs resulting in mortality. They propagate by spores, and if any are seen on your shrimp, care must be take to remove the infected shrimp immediately to minimise the spread to other shrimp.
Diagnosis:
In freshwater shrimps, the Cladogonium ogishimae or ellobiopsidae appear as green to yellow-green vegetation, reminiscent of a fungal infection.
Often the infected area is between the swimming legs of shrimp and the swimmerettes (or pleopods). It has a mould like appearance.
It's been mainly seen on shrimps imported from Asia. Possibly from poor water conditions.
Treatment:
There is evidence that a dip in formalin (Attention: carcinogenic and toxic!) could be successful.
The only treatment that I know of that has worked is medication with Formalin & Malachite green combo.
Separate infected shrimp immediately. And treat the infected shrimp outside of the tank in a hospital tank or a temporary container. Follow the product's instructions for dosage amount and duration.
Some off the shelf products with Formalin that also includes malachite green include
Fritz Mardel QuICK Cure is one such product.
Aquasonic has one too. https://www.aqualifeaquarium.com.au/aquasonic-formalin-malachite-green-solution-100ml
Kordon Rid Ick Plus also uses the same ingredients.
Seachem Paraguard
Eco Labs BSDT32 Broad Spectrum Disease Treatment https://a.co/d/97dwbNn
Chances of success and survival of the shrimp depends on how early you diagnose the issue. If left for too long, the shrimp might not survive the formalin & malachite green treatment.