Surveys of Gynaecotyla squatarolae and Microphallus koreana (Digenea: Microphallidae) Metacercariae in Two Species of Estuarine Crabs in Western Coastal Areas, Korea

To figure out the geographical distribution of Gynaecotyla squatarolae and Microphallus koreana metacercariae in Korea, shore crabs of southwestern coastal areas were examined. Eight coastal areas in Inchon-si (A), Gyeonggi-do (B), Chungcheongnam-do (C, D, and E), Jeollabuk-do (F), and Jeollanam-do (G and H) were selected, and 2 kinds of crabs, Macrophthalmus dilatatus and/or Macrophthalmus japonicus, were caught. After transportation to the laboratory, 15 crabs per each group were grouped and ground in a mortar and pestle, and examined for microphallid metacercariae. In M. dilatatus, G. squatarolae metacercariae were recovered from 3 (C, E, and H) out of 6 regions, but M. koreana metacercariae were not recovered. In the case of M. japonicus, G. squatarolae metacercariae were recovered from 6 (B, D, E, F, G, and H) of 7 areas surveyed, and M. koreana matacercariae were detected from 5 regions (A, B, D, F, and H). These results indicate that the life cycle of G. squatarolae is maintained in the western coastal areas using M. dilatatus and M. japonicus as intermediate hosts, while that of M. koreana is maintained only using M. japonicus.

Microphallus koreana n. sp. (Trematoda: Microphallidae) Transmitted by a Marine Crab, Macrophthalmus dilatatus

Microphallus species occur primarily as intestinal parasites of birds and mammals, and metacercariae of a new species belonging to this genus have been discovered from the crab, Macrophthalmus dilatatus, in the Republic of Korea. The metacercaria of this fluke was round with 2 thick walls, and the excysted one had mature genital organs. The adult flukes recovered from experimentally infected chicks had numerous intrauterine eggs, well-developed pars prostatica, widely bifurcating ceca, and prominent uterine bulge. After observing internal structures, it was concluded that this species is different from any other known Microphallus spp. Based on the morphology of metacercariae and adult flukes, we describe this specimen as a new species, Microphallus koreana n. sp.