Abstract
A new species, Boholina reducta sp. nov., was found in a brackish pool within an anchialine cave in Tra Ban Island in Bai Tu Long Bay, north Vietnam. The new species is clearly distinguished from all the six species currently known in the genus Boholina by the following unique characteristics: reduction of the septum between gonopores; narrow and pointed rostrum; basal segment of mandibular palp armed with three setae; maxillule without seta on the basal exite, and exopod with 11 setae; second and third endopodal segments of the maxilliped bearing three setae each; exopod of male right leg 5 2-segmented, with two strong and one vestigial spines on the outer margin of the distal segment; and last exopodal segment of female leg 5 bearing only one spine on the outer margin. We provide a description of the new species, along with detailed illustrations and scanning electron microscopy photographs. The identification key to Boholina species is updated as well. This is the first record of the genus Boholina from Vietnam.