A new species of parasitic copepod, Caligus tunisiensis n. sp. (Caligidae), is described based on two female specimens collected from the gills of the painted comber, Serranus scriba (L.), caught in the Mediterranean Sea, off the Tunisian coasts. The new species belongs to the Caligus productus-species group established by Boxshall & Gurney (1980) as it shares the following set of character states: (i) antenna with well-developed posterior process on proximal segment; (ii) posterior margin of distal exopodal segment of leg 1 lacking typical plumose setae, or retaining single vestigial seta; and (iii) 2-segmented exopod of leg 4 armed with IV spines on compound distal exopodal segment. Detailed morphological comparisons between the new species and the core members of the C. productus-species group revealed that the new species closely resembles with C. productus Dana, 1852 and C. temnodontis Brian, 1924. However, the new species can be distinguished from its congeners in having: (i) a female maxilliped bearing a prominent bi-lobate myxal process, opposing tip of the claw; (ii) leg 4 protopod ornamented with a patch of spinules on the posterolateral surface; and (iii) an abdomen ornamented with two rows of minute spinules at the posterolateral corners.