Serrapinnus lucindai can be primarily diagnosed from its congeners by having 17 to 19 ventral procurrent caudal-fin rays (vs. less than 17). Furthermore, it differs from other species of the genus by having the following characters: anal-fin hooks on the first unbranched and five branched rays of mature males (vs. anal-fin hooks on at least the anterior six branched rays on the remaining species of the genus); 9 to 11 cusps on the premaxillary teeth (vs. 5 in S. microdon and S. potiguar, 7 in S. aster, 7 to 9 in S. calliurus, S. heterodon, S. kriegi, S. micropterus, S. notomelas and S. piaba, and 10 to 12 in S. gracilis and S. littoris); continuous mid-lateral black stripe extending from the opercular region to the caudal-peduncle spot absent (vs. present in S. sterbai); dentary teeth without expanded cusps forming a sharp cutting edge and the incomplete lateral line (vs. dentary teeth with expanded cusps forming a sharp cutting edge and complete lateral line in S. heterodon); hyaline dorsal fin (vs. fin with a proximal black blotch in S. notomelas); and black spot absent in the posteroventral region of the abdomen (vs. present in S. kriegi) (Ref. 96959).

Description: dorsal-fin rays ii,9; anal-fin rays iii-iv,17-21; pectoral-fin rays i,9-10; pelvic-fin rays i,6-7; scale rows between lateral line and pelvic-fin origin 4 or 5 (Ref. 96959).