Abstract
Thalestris hokkaidoensis sp. nov. (Crustacea: Copepoda: Harpacticoida: Thalestridae) is described from Uchiura Bay, Hokkaido, Japan. The species infests the red alga Palmaria palmata (Linnaeus) Kuntze, living in galleries it makes in thalli. Thalestris hokkaidoensis is distinguished from congeneric species by the structure of P1 and P5.