Genitalia of Amphidromus spp A–C Amphidromus costifer Smith, 1893 from Ea Sup, Dak Lak, Vietnam (NMNS-8764-048), showing A general view of genitalia B interior structures of penis C interior structures of vagina chamber D, E Amphidromus pankowskianus Thach, 2020 from Khammouan Province, Laos, near Minh Hoa District, Quang Binh Province, Vietnam (NMNS-8764-152), showing D general view of genitalia E interior structures of penis and vagina chamber. Red dots indicate the shape of the missing gametolytic sac. Green arrows indicate the genital openings. Abbreviations: ap, appendix; e, epiphallus; fl, flagellum; fo, free oviduct; gd, gametolytic duct; gs, gametolytic sac; ov, oviduct; p, penis; pp, penial pilaster; pr, penial retractor muscle; pv, penial verge; v, vagina; vd, vas deferens; vp, vaginal pilaster.