We describe a new paranthurid isopod genus and species, Deltanthura palpus gen. et sp. nov., collected from a depth of 805–852 m off the southern coast of Mie prefecture, Japan. Deltanthura is similar to Pseudanthura Richardson, 1911 in having a triangular pleotelson, acute mandible with a 3-articulate palp, a maxillipedal endite, and a tapering uropodal exopod, but differs in having eyes and neotenous characters (reduced pereonite 7 and pereopods 7 lacking). Deltanthura and four paranthurid genera (Califanthura Schultz, 1977, Colanthura Richardson, 1902, Cruranthura Thomson, 1946, and Cruregens Chilton, 1882) share neotenous characters, but in Deltanthura the mandible is acute, with a 3-articulate palp and maxillipedal endites are present. Califanthura minuta Kensley & Heard, 1991 may belong in Deltanthura as they share the triangular pleotelson and tapering uropodal exopod, but we refrain from transferring it to Deltanthura as its description lacks the other diagnostic characters of Deltanthura. We provide a revised key to all genera in Paranthuridae Menzies & Glynn, 1968.