The newly discovered, world’s smallest frog:
http://edition.cnn.com/2012/01/12/world/asia/new-frogs/?hpt=wo_t5
The world’s smallest fish: http://en.wikipedia.org/wiki/List_of_smallest_fish_in_the_world
For a list of the world’s smallest organisms see: http://en.wikipedia.org/wiki/Smallest_organisms
