Long arm river prawn

It's a Macrobrachium tenellum (the Pacific sister species of M. acanthurus in Atlantic watersheds of the Americas). No true crayfish are native to Costa Rica, so anything of similar body form seen in a stream or river there is almost certainly a member of this genus. (That said, the aquaculture industry has brought the North American Procambarus clarkii and the Australian Cherax quadricarinatus into worldwide circulation, so it's possible that some have ended up either deliberately or accidentally introduced.) Native crayfish are in fact entirely absent from Mesoamerica south of Belize and Guatemala, and from all of tropical South America (a few species are found in the temperate southern portions of the continent).

difficult to say. you really have to do some searching on the web. it looks like that the species you suggest has opposite tail markings from your spotting. could account from genetic differences within the species. I am no expert. my recommendation is only macrobrachium sp.

most of the "crayfish" in Costa Rica are shrimp species...macrobrachium. I think the range of the mentioned crayfish above is mostly restricted to Europe.