A new species of genus Tropodiaptomus Kiefer, 1932 (Crustacea: Copepoda: Calanoida: Diaptomidae) from Thailand.

Tropodiaptomus megahyaline sp. nov. is described and illustrated based on materials collected from a rice field near Songkhram River Basin, Bueng Kan Province, Northeastern Thailand. This new species can be distinguished from its congeners by features of the male such as (1) antepenultimate segment of the right antennule with straight spinous process reaching middle of next segment; (2) basis of the right P5 with three process; (3) basis of both right and left P5 with longitudinal hyaline lamella, length about 1/3 as long as basis on the inner margin; (4) second segment of exopod of the right P5 trapezoidal, with two semicircular hyaline knobs, and one triangular process on distal outer margin of dorsal surface; and (5) inner margin of the exopod of the left P5 with the proximal part larger than the distal part. Differences among Asian Tropodiaptomus species are noted, and an identification key for both females and males of this genus is proposed. [ABSTRACT FROM AUTHOR]