Phylogenetic tree and MOTU distribution for the three sampled Red Sea Perinereis species A maximum likelihood phylogeny based on COI sequences, with information regarding the different MOTU delineation methods. Numbered MOTUs (1–4) contain original sequences from Perinereis specimens analysed in this study; MOTUs “GB” are based on Perinereis sequences mined from GenBank; MOTU “OUTG” correspond to the rooted outgroup, Alitta virens. Bootstrap values lower than 80% not displayed B Red Sea MOTU distribution; each coloured pie corresponds to a unique species and respective abundance proportion; larger pie charts indicate higher number of sympatric species. Species from the Suez Canal based on mined GenBank sequences from Elgetany et al. (2022); abundance proportion based on type material C Perinereis damietta, focus on prostomium and pharynx, dorsal view, specimen NTNU-VM-86031 D Perinereis suezensis, focus on prostomium and pharynx, dorsal view, specimen NTNU-VM-86032 E Perinereis kaustiana sp. nov., focus on prostomium and pharynx, dorsal view, specimen NTNU-VM-86011. Scale bars: 500 μm (C–E).