Two new species of Tropodiaptomus Kiefer, 1932 (Copepoda, Calanoida, Diaptomidae) from temporary waters in Thailand and Cambodia with a key to Southeast Asian species.

Two new copepod species of the species-rich genus Tropodiaptomus, collected from temporary water habitats in Southeast Asia, are described. A critical morphological comparison has revealed that the two new species, T. lannaensis sp. nov. from Thailand and T. kampucheaensis sp. nov. from Cambodia, closely resemble their respective congeners, T. ruttneri (Brehm, 1923) and T. doriai (Richard, 1894). However, T. lannaensis sp. nov. can be distinguished from other congeners, including T. ruttneri, by the following characters of the male P5: (1) the inner margin of the right basis has one small semicircular knob and one triangular knob; (2) the right second exopodal segment has a long, slender accessory spine inserted at the proximal third of the outer margin; and (3) the inner margin of the left exopod has a bilobed saw with a series of large denticles and smaller denticles near the distal end. Tropodiaptomus kampucheaensis sp. nov. is different from all other species because it has (1) only one longitudinal hyaline lamella on the inner margin of the basis of the male right P5; (2) the one-lobed distal inner margin on the male left P5 exopod with uniform teeth; (3) the asymmetrical female genital-double somite (right margin expanded sub-proximally); and (4) the extraordinarily long inner seta on the P4 coxa of both sexes. The biogeography and keys to the species of Tropodiaptomus in Southeast Asia are presented.