Genus Syllis Savigny in Lamarck, 1818

Type species. Syllis monilaris Savigny in Lamarck, 1818 .

Diagnosis. Body cylindrical of variable size, from relatively medium-sized to large, compared to most syllids. Subpentagonal prostomium, with 1 pair of palps totally free from each other or fused at bases, 3 antennae, 2 pairs of eyes and, sometimes, 1 pair of anterior eyespots. Peristomium usually shorter than segments, with 2 pairs of peristomial cirri; border between prostomium and peristomium usually with conspicuous nuchal organs, as 1 pair of ciliated grooves. Antennae, peristomial cirri, dorsal cirri throughout and anal cirri moniliform; ventral cirri short, digitiform. Parapodia with compound falcigers, some taxa with secondarily simple chaetae, due to fusion between shaft and blade, or loss of blade; spiniger-like chaetae frequently present; dorsal and ventral simple chaetae usually present on posterior chaetigers. Pharynx with large tooth on anterior border or slightly posteriorly to opening, trepan absent (Nogueira & San Martín 2002; Nogueira & Yunda-Guarin 2008). Reproduction by stolonization, with stolons with different morphologies, according to species. Some species viviparous.

Remarks. The largest genus in the family, Syllis, as currently conceived, seems to be paraphyletic, according to phylogenetic analyses performed on the family (Aguado et al. 2007, 2012). However, until more detailed studies are made specifically on this genus, we follow herein the opinion of most authors (e.g., San Martín 2003; Álvarez- Campos et al. 2015a, b), considering Typosyllis Langerhans, 1879 as a junior synonym of Syllis .