<i>Metagonimus yokogawai</i> (Trematoda: Heterophyidae): From Discovery to Designation of a Neotype

Abstract

Metagonimus yokogawai (Katsurada, 1912) Katsurada, 1912 (Trematoda: Heterophyidae) is parasitic in the small intestine of mammals including man and birds in Far Eastern Russia, Korea, Japan, China, and Taiwan. In the present study, the metacercariae and adults of M. yokogawai were redescribed to designate a neotype of this fluke together with reviews of previous studies including study histories from the first discovery to now. We particularly, attempted to review the study histories and morphological descriptions of M. yokogawai for the species validity, and compared with the morphological characteristics and life cycles of the closely related species, Metagonimus takahashii and Metagonimus miyatai. Finally, we proposed a differential key for the 8 known Metagonimus species distributed in East Asia. Metacercariae were obtained from the body muscles of sweetfish (Plecoglossus altivelis) collected in the Asahi River at Takebe-cho, Kita-ku, Okayama City, Okayama Prefecture, Japan. Adults were recovered from the small intestine of Syrian golden hamsters, to which the metacercariae had been fed 14 days before. A neotype was selected out of the present adult specimens. The Asahi River at Takebo-cho became the type locality of M. yokogawai. In conclusion, the present review shows that M. yokogawai, M. takahashii, and M. miyatai are valid and discriminated by means of morphological characteristics.

The life cycle of a zoonotic parasite reassessed: Experimental infection of Melanoides tuberculata (Mollusca: Thiaridae) with Centrocestus formosanus (Trematoda: Heterophyidae)

“…Regarding the formation of miracidia in representatives of the family Heterophyidae, two processes were described: the release of embryonated eggs by the parasite, and the formation of miracidia in the environment. The first phenomenon was the most frequent, as can be verified in species belonging to the genera Ascocotyle [ 31 – 33 ], Haplorchis [ 34 , 35 ], Heterophyes [ 36 ], Metagonimus [ 37 , 38 ], Pygidiopsis [ 39 , 40 ], Stellantchasmus [ 41 ] and Stictodora [ 42 ]. On the other hand, release of immature eggs that embryonate in the external environment, after incubation for 10–23 days, depends on the species.…”

Description of Metagonimus pusillus sp. nov. (Trematoda: Heterophyidae): phylogenetic relationships within the genus

“…Adult worms, obtained here as a result of an experiment, corresponded to the Metagonimus genus in all morphological parameters (the structure of the reproductive system and the topology of organs). They, like M. katsuradai , M. otsurui , M. hakubaensis and M. minutes (table 2), refer to Metagonimus worms in which the body size of mature individuals does not exceed 0.650 mm (Besprozvannykh et al ., 1987; Saito et al ., 1997; Shimazu & Kino, 2015; Shumenko et al ., 2017). Therefore, we conducted a comparative morphometric analysis only for these species.…”

Small intestinal flukes of the genus Metagonimus (Digenea: Heterophyidae) in Europe and the Middle East: A review of parasites with zoonotic potential

“…Metagonimus romanicus differs from M. yokogawai, redescribed by Shimazu and Kino [81], by the presence of a prepharynx and a long oesophagus in M. romanicus (the prepharynx is absent in M. yokogawai and the oesophagus is short), the position of the ventral sucker (equatorial versus clearly pre-equatorial in the latter species) and the ovary (at 2/3 of the body length versus almost equatorial in the latter species), the anterior extension of the vitelline follicles (limited to the posterior third of the body in M. romanicus, whereas in M. yokogawai they extend almost to the middle of the body) and the posterior extension of the uterus (the uterus extends almost to the posterior margin of the posterior testis in M. romanicus, whereas in M. yokogawai it only reaches the anterior margin of the posterior testis) (see Figs. 1A, 1B, 1D-1F, 2A-2G, 3, 6C in this paper and Figs.…”

“…1A, 1B, 1D-1F, 2A-2G, 3, 6C in this paper and Figs. 1-6 in [81]). Metagonimus romanicus differs from all but one (M. ciureanus) known species of the genus Metagonimus by the presence of a prepharynx [67,81,82,94].…”

“…Pars prostatica not observed. Ejaculatory duct short, thick-walled, slightly sinuous, joining metraterm to form short, thick-walled hermaphroditic duct (called genital atrium by Shimazu and Kino [81]), opening into ventrogenital sac (Fig. 1C).…”