Trematode metacercariae parasitic in the estuarine crustacean Cyathura muromiensis Nunomura, 1974 (Peracarida: Isopoda: Anthuroidea)

This is the first report of trematodes parasitic in the estuarine isopod crustacean Cyathura muromiensis, and the fourth report from anthuroid isopods worldwide. From 52 of 54 host individuals collected qualitatively on the tidal flat of the Muromi River estuary, Fukuoka, Japan, 389 cysts of metacercariae were extracted (sample prevalence = 96.3 %). Host individuals contained from one to 71 metacercarial cysts. The range in cyst diameter was 172.3–252.1 μm, and the distribution of cyst sizes contained only one component. Cysts occurred in pereonites 2–7 and the pleon of the host, but not in the head, pereonite 1, or telson. There was no correlation between the number of cysts and host sex or size. Sequences of the nuclear “ITS1 region,” from the 3´ region of 18S rRNA to the 5´ region of internal transcribed spacer I gene (ITS1), from five cysts ranging in size from nearly the lowest diameter to the greatest diameter in our sample showed p-distances of 0.0–0.2 %, suggesting that all cysts obtained were conspecific. A phylogenetic reconstruction based on nuclear 28S rRNA gene sequences showed that the trematode belongs in the genus Microphallus. The definitive host of our trematode species is likely a bird, since the definitive hosts of microphallids are chiefly birds, and birds are known to prey on Cyathura isopods.