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Despite the many publications concerning the isolation of substances and the many reviews of marine natural products, some groups of organisms remain poorly studied, including “Polychaeta”. In response, this review covers articles published through December 2016 that address marine natural products produced from polychaetes, with a focus on antipredatory strategies, competitors, fouling, and pathogens. A total of 121 compounds were isolated from 1934 to 2016, which includes halogenated aromatics, proteins, amino acids and Lumazine derivatives most notably—with a defensive function were found in the literature, most frequently in the families Sabellidae, Terebellidae, Glyceridae, and Nereididae. The period of highest discovery of natural products in defensive actions for the group was the 2000s. Polychaetes were addressed in 26 revisions of the total 51 articles analyzed and are less reported than other marine invertebrates such as sponges, cnidarians, mollusks, and tunicates. In sum, the present review provides a basis for future research on the marine chemical ecology of polychaetes.

We identified publication trends and methodological changes in polychaete ecotoxicological studies since the review carried out by Reish and Gerlinger (Bull Mar Sci 60:584–607, 1997) using a classic review approach. We also carried out a meta-analysis to identify the overall effect of the type of pollutants (e.g., hydrocarbons, metals, pesticides) and to test the consistency of their effect at different levels of analysis (e.g., biochemical, physiological, behavioral) using 14 different biological responses (e.g., bioaccumulation, tolerance, enzymatic activity). A total of 136 articles met the selection criteria and were analyzed for the classic review. Main findings include: (1) studies focused on the effects of metals (48%), hydrocarbons (32%), and pesticides (20%); (2) sublethal effects were more frequent; and (3) the nereidid species Hediste diversicolor was the most studied species. For the meta-analysis, 27 articles met the selection criteria and a total of 168 effect sizes were calculated. The results from the generalized linear mixed models (GLMMs) indicated that the hydrocarbons have the strongest effect in polychaetes, while the most sensitive metric is behavior. Enzymatic activity and mortality represented the most sensitive biological responses to estimating the magnitude and direction of the effect. Finally, the tendencies observed in the classic review did not represent the strongest effects in the GLMMs.

Species definition is not an easy task, when considering the more than 27 known species concepts. Among them, the morphospecies concept has been one of the most applied since it is based on the use of observable morphological features. Morphometry has been used to delimitate morphospecies or similar taxa complementing the morphological observations and contributing to clarify taxonomic problems. Specimens from the sympatric species Perinereis anderssoni and Perinereis ponteni, collected from the north-eastern to southern coast of Brazil and considered synonymous by some authors, were compared through morphometric analyses for the evaluation of their taxonomic status. Morphometric analysis indicates that notopodial cirri lengths in the median and posterior regions on the body clearly allowed differentiation between the two species. Our results indicate that the number and arrangement of paragnaths demonstrate a pattern of variation that effectively differs and could be used to discriminate these two Perinereis species. This distinction was confirmed by the restricted among-population variability within each species, even when populations that are geographically very distant from each other were considered.