Additions to the taxonomy of Americabaetis (Ephemeroptera : Baetidae): A-lugoi, n. sp., adult of A-robacki, and key to larvae

Americabaetis lugoi is a distinctive new species of the small minnow mayfly family Baetidae and is described from female larvae and adults collected i n Costa Rica. Extensive samples of the new species indicate that it is part henogenetic. Larvae of A. lugoi share a frontal keel with certain other spe cies of Americabaetis, but A. lugoi larvae differ from all other known spec ies of the genus in mouthpart, paraproct, and other characteristics. Adults of A. robacki are described for the first time, based on reared material f rom Uruguay. They are diagnostically compared with A. alphus, the only othe r South American species known as an adult. A key to the larvae of all know n Americabaetis species is provided.