1	Pharyngeal tooth absent; pharynx with an incomplete trepan formed by few teeth, backwardly directed	Odontosyllis
–	Pharyngeal tooth present, with or without trepan	2
2	Pharynx with mid dorsal tooth and an incomplete arc of small denticles, frontally directed	3
–	Pharynx without denticles, only the mid dorsal tooth	4
3	All dorsal cirri long to very long, coiled over dorsum. Pharyngeal armature composed of a mid dorsal tooth and an incomplete arc of few (5–6) denticles	Dioplosyllis
–	Dorsal cirri not so long. Mid dorsal tooth and incomplete (sometimes complete) arc of numerous (around 30–40) pharyngeal denticles	Eusyllis
4	Antennae, tentacular cirri and dorsal cirri of chaetiger 1 long; subsequent dorsal cirri short	5
–	All appendages long	6
5	Body minute; strictly interstitial. Without enlarged, aciculiform ventral simple chaetae	Neopetitia
–	Body not so small; found on hard substrata. With enlarged, aciculiform, ventral simple chaetae	Brevicirrosyllis
6	Pharyngeal tooth on middle or posterior position or distinctly retarded	7
–	Pharyngeal tooth located on anterior margin	8
7	A number of anterior parapodia with enlarged aciculae, distally knobbed	Streptodonta
–	Without these enlarged aciculae	Opisthodonta
8	Segments posterior to proventriculus fused in units of 2–3 segments. Palps completely separated	Synmerosyllis
–	Segments not fused. Palps separated or basally fused	9
9	Without eyes (nuchal pigment patches may be present on prostomium). Palps long, fused to prostomium. Dorsal cirri of midbody short	Palposyllis
–	With eyes. Palps not so long nor fused to prostomium. Dorsal cirri long throughout body	10
10	Antennae and anterior dorsal cirri more or less articulated. A digitiform, subcirral papilla, below the bases of dorsal cirri	Paraehlersia
–	All appendages smooth. Without subcirral papillae	11
11	Small to minute size (< 5 mm in length). Palps separated. Pharynx shorter than proventriculus, with a long tooth. Compound chaetae unidentate or with small, spine-like proximal teeth	Nudisyllis
–	Medium to large size (> 5 mm in length). Palps fused basally. Pharynx similar in length or longer than proventriculus. Compound chaetae bidentate	Pionosyllis