Marine biodiversity is threatened and comprehensive assessments of marine species are needed for biodiversity management and research priorities, especially for little-studied areas and taxa. The region of the Ryukyu Islands, in subtropical southern Japan, is a marine biodiversity hotspot, however most marine invertebrate taxa here can be considered grossly understudied. Despite the known high diversity of marine annelids, both in terms of species richness and ecological functions, a review of the knowledge accumulated on them in the Ryukyus is not yet available. To provide an overview of past research and identify gaps, we reviewed 149 publications related to the topic and compiled 1986 literature records. Despite large discrepancies in groups and environments studied, we found indications of high diversity of marine annelids in the Ryukyus, with 445 nominal species recorded, including 59 described from the region, comprising approximately a quarter of Japan’s marine annelid fauna. However, unequal sampling effort was observed across the Ryukyus, with Okinawa-jima and Amami-Oshima being the most well-investigated islands, whereas Yakushima and Miyako-jima were almost completely uninvestigated. Intertidal and sand bottoms were the most well-studied environments, while coral reefs have been scarcely studied. Much more research is needed to understand marine annelid diversity in the Ryukyus, with taxonomic work needed for all families supported by sampling expeditions to underexplored islands and environments, with follow-up studies on ecology, reproduction, and marine natural products also sorely needed. Thus, despite indications of very high diversity, we conclude that marine annelid research in the Ryukyus is still nascent.