How many catfish are there?
The old story goes that JBS Haldane felt that God had an inordinate fondness for beetles. It also seems he likes catfish. CJ Ferraris has produced a checklist of fossil and living catfishes and estimated that there are 3093 valid species in 478 genera (and 36 families). Of these 72 species are known solely from fossils. No one who knows catfishes will be surprised that the largest family is the Loricariidae (716 species in 96 genera), but interestingly, three genera of living catfishes could not be assigned to existing families: Conorhynchos and Phreatobius from South America, and Horabagrus from Asia.
Update: Fixed dumb homonym mistake. Sheech!