1	All chaetae simple, usually thick	Haplosyllis
–	Compound and capillary chaetae present dorsally and ventrally (sometimes some chaetae in mid body appear simple by blade and shaft fusion but typical compound chaetae also present anteriorly)	2
2	Body small, dorso-ventrally flattened. Antennae, tentacular and dorsal cirri reduced to a single, spherical article	3
–	Body of medium to large size, cylindrical or flattened. Antennae, tentacular and dorsal cirri with several articles (moniliform)	4
3	Palps fused. Two dorsal rows of spherical tubercles, similar to dorsal cirri	Eurysyllis
–	Palps separated. Without dorsal tubercles	Plakosyllis
4	Body cylindrical	Syllis
–	Body dorso-ventrally flattened	5
5	Dorsum, as well as antennae and dorsal cirri, with papillae and longitudinal grooves. Pharynx unarmed	Xenosyllis
–	Without longitudinal grooves on dorsum (minute transverse rows of papillae, difficult to see) (one species densely papillated). Pharynx with a trepan and, occasionally, a tooth	Trypanosyllis