Orbinia Quatrefages, 1865

Sun, Yue & Li, Xinzheng, 2018, Orbinia wui, a new species from China, with redescription of O. dicrochaeta Wu, 1962 (Annelida, Orbiniidae), Zootaxa 4403 (2), pp. 351-364 : 362-363

Key to species of Orbinia Quatrefages, 1865

1 Branchiae from anterior thoracic chaetigers (usually chaetigers 5–6), thoracic neuropodial postchaetal lobes fimbriated with more than three papillae...Group A........................................................................ 2

- Branchiae from middle and posterior thoracic chaetiger (usually posterior to chaetiger 8), thoracic neuropodial postchaetal lobes only with 1–3 papillae...Group B.................................................................... 14

2 Change in structure of thoracic neuropodial uncini from anterior to posterior of thorax............................... 3

- No distinct change in structure of thoracic neuropodial uncini from anterior to posterior of thorax...................... 4

3 Thorax with 13–16 chaetigers, first 6 chaetigers with rows of uncini and subsequent thoracic chaetigers with rows of subulun- cini................................................................................... Orbinia wui sp. n.

- Thorax with 19 chaetigers, anterior thoracic chaetigers with serrated uncini while posterior chaetigers with smooth uncini............................................................................. Orbinia armandi ( McIntosh, 1910)

4 Thorax with 50 chaetigers, thoracic neuropodial uncini smooth, interramal cirri present.......... Orbinia monroi Day, 1955

- Thorax with less than 50 chaetigers, thoracic neuropodial uncini smooth or serrated................................. 5

5 Furcate chaetae present in abdominal notopodia............................................................. 6

- Furcate chaetae absent in abdominal notopodia............................................................. 17

6 Thoracic neuropodial uncini bent but smooth, interramal cirri present.................... Orbinia bioreti ( Fauvel, 1919)

- Thoracic neuropodial uncini serrated, with longitudinal median groove, interramal cirri absent.................................................................................................... Orbinia papillosa ( Ehlers, 1897)

7 Interramal cirri present................................................................................. 8

- Interramal cirri absent.................................................................................. 9

8 Thorax with 22–24 chaetigers................................................. Orbinia sertulata ( Savigny, 1822)

- Thorax with 30–33 chaetigers................................. Orbinia latreillii (Audouin & H Milne Edwards, 1833)

9 Flail chaetae present in abdominal neuropodia, thorax with 21 chaetigers................. Orbinia americana Day, 1973

- Flail chaetae absent in abdominal neuropodia.............................................................. 10

10 Thorax with more than 30 chaetigers..................................................................... 11

- Thorax with less than 30 chaetigers...................................................................... 12

11 Thorax with 35–38 chaetigers, thoracic neuropodial uncini smooth, with lateral sheath....... Orbinia cornidei ( Rioja, 1934)

- Thorax with 31 chaetigers, thoracic neuropodial uncini serrated......................... Orbinia swani Pettibone, 1957

12 Without subpodial lobes...................................................... Orbinia exarmata ( Fauvel, 1932)

- With subpodial lobes on several chaetigers................................................................. 13

13 Thorax neuropodia with crenulated capillaries............................... Orbinia angrapequensis ( Augener, 1918)

- Thoracic neuropodia without capillaries......................................... Orbinia glebushki Averincev, 1990

14 Interramal cirri absent................................................................................. 15

- Interramal cirri present................................................................................ 17

15 Flail chaetae absent in abdominal neuropodia, neuropodial uncini blunt and serrated........ Orbinia johnsoni ( Moore, 1909)

- Flail chaetae present in abdominal neuropodia, neuropodial uncini smooth....................................... 16

16 Furcate chaetae absent in abdominal notopodia, with 3–4 capillaries........... Orbinia camposiensis Leão & Santos, 2016

- Furcate chaetae present in abdominal notopodia, with one half row of capillary.............. Orbinia hartmanae Day, 1977

17 Interramal cirri only present in thoracic parapodia.................................... Orbinia orensanzi Blake, 2017

- Interramal cirri only present in abdominal parapodia......................................................... 18

- Interramal cirri present in thoracic and abdominal parapodia................................................... 19

18 Stomach papillae forming ventral fringe on chaetigers 15–17...................... Orbinia vietnamensis Gallardo, 1968

- Stomach papillae present on first 3 abdominal chaetigers, numbering only up to 8......................................................................................... Orbinia oligopapillata López, Cladera & San Martín, 2006

19 Furcate chaetae absent in abdominal notopodia........................................... Orbinia dubia Day, 1955

- Furcate chaetae present in abdominal notopodia............................................................ 20

20 Thorax with 24–27 chaetigers, branchiae from chaetiger 11–13......................... Orbinia dicrochaeta Wu, 1962

- Thorax with 19 chaetigers, branchiae from chaetiger 10.............................. Orbinia riseri ( Pettibone, 1957)