Former selected drawings of O. similis / helgolandica. A, B O. spinifrons Boeck, 1864 (=? O. helgolandica Claus), female body and “one of swimming feet” (= leg 4?) (after Brady1878, Plates XIV and XXIV A) C–F O. similis exopod of legs 1 to 4 (after Gisbrecht 1893, Plate 34) G–J O. helgolandica, female body, legs 1-2 and leg 4 (after Sars 1913, Plate III) K–O O. similis, female body and legs 1 to 4 (after Nishida 1985, fig. 50 and 51). Original illustrations were faithfully copied in all details and rearranged to facilitate comparisons. Scale bars only provided in Nishida (1985).