Nemertean egg predators cause high egg mortality for several commercially important crustacean species. Variation in space and time as well as the interaction between these symbionts and the fishery are reviewed. A method to separate egg mortality caused by nemertean worms from other
mortality sources is presented. The impact of these egg predators is discussed with respect to both individual host and population perspectives. Potential effects of nemertean egg predators are hypothesized with respect to host aggregation, molting, copulation, oviposition, breeding seasonality,
burial of females during brooding, and grooming behavior. We suggest that the paucity of nemertean egg predators on Caridea may be associated with the rapid ecdysial process, rapid deposition of external spermatophores during mating and the highly specialized grooming appendages which remove
egg predators from the egg mass. Many species of Anomura, Palinura and Astacidea share some of these traits, and nemerteans have been infrequently reported as egg predators from these taxa. In contrast, the Brachyura molt slowly, have internal fertilization with associated intimate pre- and
post-copulatory embraces, and lack specialized grooming appendages. These traits may facilitate the transmission and maintenance of high population densities of nemertean egg predators on brachyuran host populations.
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