The acoel worm Symsagittifera roscoffensis, an early offshoot of the Bilateria and the only well‐studied marine acoel that lives in a photosymbiotic relationship, exhibits a centralized nervous system, brain regeneration, and a wide repertoire of complex behaviors such as circatidal rhythmicity, photo/geotaxis, and social interactions. While this animal can be collected by the thousands and is studied historically, significant progress is made over the last decade to develop it as an emerging marine model. The authors here present the feasibility of (...) culturing it in the laboratory and describe the progress made on different areas, including genomic and tissue architectures, highlighting the associated challenges. In light of these developments, and on the ability to access abundant synchronized embryos, the authors put forward S. roscoffensis as a marine system to revisit questions in the areas of photosymbiosis, regeneration, chronobiology, and the study of complex behaviors from a molecular and evolutionary perspective. (shrink)