Limnopilos naiyanetri is an extremely small species of crab from Thailand. These tiny filter feeders only reach about 1cm wide without the legs! Care is similar to dwarf shrimp such as Neocaridina sp. these crabs can be eaten by all but the smallest and most passive of fish, so its recommended to keep them with invertebrates only, or tiny species such as Corydoras pygmaeus or Boraras sp. if you do want fish.
Currently the crabs average around 2-3mm wide in the carapace, or around 1-1.5cm with the legs outstretched.