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 <i>Tropodiaptomus</i>, collected from temporary water habitats in Southeast Asia, are described. A critical morphological comparison has revealed that the two new species, <i>T. lannaensis</i> <b>sp. nov.</b> from Thailand and <i>T. kampucheaensis</i> <b>sp. nov.</b> from Cambodia, closely resemble their respective congeners, <i>T. ruttneri</i> (Brehm, 1923) and <i>T. doriai</i> (Richard, 1894). However, <i>T. lannaensis</i> <b>sp. nov.</b> can be distinguished from other congeners, including <i>T. ruttneri</i>, 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. <i>Tropodiaptomus kampucheaensis</i> <b>sp. nov.</b> 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 <i>Tropodiaptomus</i> in Southeast Asia are presented.