(Adapted from: Fauchald 1982 b, Gil 2011)
1 All branchiae simple and strap-like........................................................................ 2
- Branchiae bifid or pectinate............................................................................. 4
2 Branchiae from chaetiger 1; pseudocompound hooks all tridentate; ventral cirri cirriform on the first 5–7 chaetigers; cirriform postchaetal lobes distinct on the first 10–13 chaetigers........................................................ 3
- Branchiae from chaetiger 5; pseudocompound hooks bi– and tridentate; ventral cirri cirriform on the first 4 chaetigers; cirriform postchaetal lobes distinct on the first 16–33 chaetigers in adults............................................................................................... Onuphis farensis sp. nov. (Gulf of Cádiz, SW Iberian Peninsula)
3 Maxillary formula: MI: 1 + 1, MII: 8-9 + 8, MIII: 9-10 +0, MIV: 5-6 + 5, MV: 1 + 1.................. O. opalina (SE Iceland)
- Maxillary formula: MI: 1 + 1, MII: 6-8 + 8-9, MIII: 7-8 +0, MIV: 7-9 + 9-11, MV: 1 + 1....... O. rullieriana (SW British Isles)
4 Branchiae pectinate, with up to 5–7 branchial filaments (first 15–20 chaetigers with simple branchiae)................. 5
- Branchiae bifid (first 20–25 chaetigers with simple branchiae); ventral cirri cirriform on the first 3–4 chaetigers; digitiform postchaetal lobes disappearing at chaetiger 7–8....................... O. falesia (Gulf of Follonica, Mediterranean Sea)
5 Tridentate pseudocompound hooks present on the first 3 chaetigers; branchiae pectinate, with up to 6–7 branchial filaments (first 18–20 chaetigers with simple branchiae); ventral cirri cirriform on the first 6 chaetigers; digitiform postchaetal lobes distinct in at least 60 chaetigers............................. O. eremita (European Atlantic coast and Mediterranean Sea)
- Bi – and tridentate pseudocompound hooks present on the first 2 chaetigers; branchiae pectinate, with up to 5–6 branchial filaments (first 15 chaetigers with simple branchiae); ventral cirri cirriform present from the first chaetiger, but total number unknown; digitiform postchaetal lobes present from the first chaetiger, but total number unknown...................................................................................... O. pancerii (Naples region, Mediterranean Sea)