Abstract:All 6 naupliar stages of Eucyclops cf. serrulatus tropicalis Dussart and Fernando, 1985, Euc. cf. spatulatus Morton, 1990, and Ectocyclops medius Kiefer, 1930 are described from Bangkok, Thailand. Naupliar differences at the genus level were more pronounced than those at the species level in Eucyclops and Ectocyclops (Ectocyclops having a particularly large, round-shaped labrum, and strong spinules on the anterior surface of the coxa, basis, and endopod). Species-specific naupliar characters allow interspecific discrimination (Euc. cf. serrulatus tropicalis differs from Euc. cf. spatulatus particularly in its smaller size, in the relative length of the distal antennal exopod segment, and in showing a transverse row of small spinules along the caudal rim).