The Genera Platorchestia and Demaorchestia (Amphipoda, Talitridae, Talitriinae) from Seashores of Japan

Seventy-three male specimens of ”Platorchestia platensis”from Japan were inspected on 13 morphological characters. Most characters revealed high variation. The coxa and propodus of gnathopod 2 and the carpus of pereopod 7 indicated that the specimens comprised two species: Platorchestia pacifica Miyamoto and Morino, 2004 and Demaorchestia joi (Stock and Biernbaum, 1994) sensu lato. Both species were rediagnosed.　Demaorchestia hatakejima Lowry and Myers, 2022 was synonymized to P. pacifica. A key to allied species in Platorchestia and Demaorchestia from Japan and the surrounding countries was given.