Tomopterids are a family of highly-derived, holopelagic, gelatinous polychaetes found throughout the ocean. They are distinguished from other polychaetes by their lack of internal segmentation and chaetae, combined with large paddle-like appendages (parapodia). Paddling of the fleshy parapodia and lateral body movement allow these animals to swim with a strikingly elegant motion that is visually distinct from other swimming polychaetes, such as nereids. We collected living tomopterids using remotely operated vehicles in California’s Monterey Bay National Marine Sanctuary, and used high-speed particle image velocimetry (PIV) and brightfield imaging to study their swimming kinematics. We found that during straight, forward swimming, thrust is generated by active paddling of the parapodia, as well as a forward-directed body wave. This body wave also increases the range of motion of the parapodia, resulting in increased advancement of the body per stroke. The characteristics of the stroke deviate from existing simplified metachronal models for polychaetes and crustaceans, and PIV measurements revealed fluid interactions between adjacent appendages. Compared to other marine polychaetes which tend to have smaller parapodia, the body wave in tomopterids provides less direct thrust, and locomotion is dominated by active paddling of parapodia. Compared to euphausiids, stroke angle and frequency were similar, but flexible appendages, planar body symmetry and the body wave result in distinct kinematics.