Description of a new species, Actus hagiangensis (Mononchida, Mylonchulidae) from Ha Giang province, Vietnam

Actus hagiangensis sp. nov. is described and illustrated from Vietnam. Females of the new species are characterized by medium body size (L = 1.1-1.4 mm), barrel shaped buccal cavity of medium size (26-31 x 13-15 mu m) with dorsal tooth apex located 75-81% of buccal cavity length from base and two longitudinal subventral rows, each with four rasp-like denticles; reproductive system didelphic-amphidelphic, vagina short with distinct par refringens vaginae, sclerotized pieces globular in optical section; tail elongate-conoid, slightly ventrally arcuate, with three caudal glands and prominent spinneret. Male with spiculcs 46 mu m in length, and slender, slightly curved gubemaculum, 12 mu m long, without accessory piece. This is the first report of a male specimen of the genus Actus. The new species is close to A. salvadoricus but differs by the larger buccal cavity, more anterior position of the dorsal tooth apex and more rounded vaginal sclerotized pieces.