Nauplius larvae (Stages I–VI) and cyprids of Tetraclita squamosa (Brugiére, 1789) and Tetraclita japonica (Pilsbry, 1916) were cultured and their morphologies compared using light microscopy and scanning electron microscopy (SEM). Using a mixture of Skeletonema costatum Greville, 1866, Isochrysis galbana Parke, 1938, and Tetraselmis Stein, 1878, sp. as food, the larvae of both species completed naupliar development and metamorphosed to cyprids in ∼14 days at 20°C. The body shape and size of the larvae of both species are similar. The major diagnostic morphological difference is the setation of the antennulae and mandibulae. From Stage V to VI, the antennulae of T. japonica bear one more preaxial seta than T. squamosa. From Stage IV to VI, the mandibulae of T. japonica also bear one more simple seta on the endopodite than T. squamosa. The size, shape, antennular morphology, and surface sculpturing of the cyprids of the two species are similar when observed under SEM. The morphology of T. squamosa and of T. japonica is compared with those of the larvae of other Tetraclita species, and taxonomic relationships within the possibly monophyletic Tetraclitidae are discussed.