Non-destructive approach using micro-CT for understanding the strategy of mesoparasitism of the genus Cardiodectes (Copepoda: Siphonostomatoida: Pennellidae) on marine fishes, with a new species description from coastal waters of the Ryukyu Islands, the western North Pacific

Abstract A new species of pennellid copepod (Siphonostomatoida), Cardiodectes laybackinabaueroides sp. nov., is described based on postmetamorphic adult females collected from the coastal waters of the Ryukyu Islands, western North Pacific, Japan. The new species differs from other congeners by having the following unique characters: the cephalothorax bearing three pairs of lateral lobes, the first to third pedigerous somites formed a swollen bulge, the elongate trunk constricted at posterior four-fifth length. The new species has only been collected from the waters around the middle to northern Ryukyu Islands, suggesting it might be endemic to that area. While other known congeners penetrate only their head to neck region into the body of their host, almost all of the body of the new species is embedded except the short posterior portion behind the constriction of the trunk and the egg strings. Non-destructive, microcomputed tomography (micro-CT) imaging was performed to obtain data on the position of the new species within the body of their host and the impact on the host internal organs. Our observations suggest that C. laybackinabaueroides sp. nov. is attached to the kidney and feeds on venous blood. This study is the first attempt to elucidate the attachment pattern of pennellid copepods within the hosts and the pathological effects using micro-CT.