AbstractAlthough researchers have examined numerous marine organisms' compensatory characteristics to minimize predation pressure, few have investigated the defensive mechanisms of polychaetes, despite their diversity. Thus, our study's aim was to evaluate the palatability and defensive strategies, both chemical and structural, in the polychaetes Branchiomma luctuosum, Perinereis anderssoni, Phragmatopoma caudata, Eurythoe complanata, and Timarete sp. Another twofold aim was to determine, by comparing our results with the literature, any latitudinal difference in the defensive strategies of E. complanata and to assess defensive mechanisms and palatability in relation to individuals' mobility, overtness, body regionalization, and color. Specimens were collected at Boa Viagem and Itaipu Beaches in Niterói, Rio de Janeiro, Brazil. In assays, a generalist consumer, the hermit crab Calcinus tibicen, was used to evaluate palatability and defenses. In palatability assays of live tissue of the polychaetes, consumers were offered a fresh piece of each polychaete to gauge their acceptance or rejection; in artificial food assays to test extracts of the polychaetes, artificial bait containing extracts of the polychaetes was offered to crabs to identify any chemical defense. Although the extracts of B. luctuosum, E. complanata, P. caudata (i.e., opercular crown), and Timarete sp. were not palatable to the consumers, extracts of P. anderssoni and P. caudata (i.e., body) were. Moreover, the opercular crown of P. caudata and the branchial crown of B. luctuosum showed evidence of structural and chemical defenses. The results corroborate past findings, suggesting no latitudinal variation in the defensive strategies of E. complanata. In general, less motile and more exposed species, aposematic or dark in color, exhibited greater investment in defensive strategies and unpalatability.