Descriptions of three new species of South African Syllidae Grube, 1850 (Polychaeta) and range confirmation of Syllis amicarmillaris Simon, San Martín & Robinson, 2014

The understanding of South African polychaetes has greatly benefited from John Dayʼs seminal contributions, particularly his 1967 monograph. However, many of the species he documented were described as non-endemic or cosmopolitan. Some of these may in fact represent distinct species, leading to an underestimation of the true diversity of Southern African polychaetes. This study examines four species belonging to the highly diverse and morphologically variable family Syllidae. Three of these were previously identified as Syllis prolifera, Syllis variegata, and Paraehlersia ferruginea based on Day’s monograph. Detailed morphological analyses and comparisons with Day’s material reveal that these specimens represent new species, which are described and illustrated here. The fourth species was identified as Syllis amicarmillaris following Simon et al. (2014), despite its occurrence approximately 250 km from the type locality. Our observations confirm that this population corresponds to S. amicarmillaris, with the only noted differences being related to the smaller size of our specimens, compared to the type description. Our results suggest that syllid diversity in South African waters is likely underestimated, and that further expanding molecular sampling —especially within syllid species complexes— will be essential to uncover hidden diversity and clarify species boundaries.