Morphological and molecular investigations of the rhizocephalan barnacle Peltogaster lineata Shiino, 1943 in the northern part of the species range (Peter the Great Bay, the Sea of Japan)

A parasitic rhizocephalan barnacle Peltogaster lineata Shiino, 1943 (Cirripedia, Rhizocephala, Peltogastridae) was found in Vostok Bay (Peter the Great Bay, the northwestern Sea of Japan), on young specimens of the hermit crab Pagurus brachiomastus (Thallwitz, 1891). This rhizocephalan was described using molecular and morphological methods. The reproductive organs were investigated by histological methods. Cuticle was visualized using SEM. Peltogaster lineata from Japanese, Korean, and Russian waters turned out to be very similar by the molecular markers and by the morphology of the externa. Peltogaster lineata differs from Peltogaster reticulata Shiino, 1943 occurring in Russian waters by the molecular markers, the shape and color of the externa, the shape of the retinacula, and the length of the receptacle ducts. Hyperparasitic isopod Liriopsis pygmaea (Rathke, 1843) was found in the externa of P. lineata for the first time. The host preference of P. lineata was changing from Pagurus filholi + Pagurus nigrivittatus + Pagurus maculosus in Japan to P. filholi + P. brachiomastus in Korea and to only P. brachiomastus in Russia. At present, Peter the Great Bay is the northern border of the distribution range of P. lineata.