Prosthiostomum huidongense sp. nov. A. Photograph of entire body, 20230421A1 (left, living specimen in dorsal view), MBM287881 (middle, preserved specimen in dorsal view, paratype), MBM287880 (right, preserved specimen in ventral view, holotype); B. Schematic diagram of head, showing arrangement of the eyes; C. Magnification of head, dorsal view (holotype); D. Magnification of genital pore and sucker (paratype). Abbreviations: fg – female gonopore; mg – male gonopore; ph – pharynx; su – sucker. Scale bars: 1 mm.