Updated key to North Atlantic species of Ampharete

The presented key for described species constitutes an update of the key 2 proposed by Parapar et al. (2019), based on species descriptions from Holthe (1986) and Parapar et al. (2012, 2018), following the term intermediate uncinigers after Imajima et al. (2012). Accordingly, intermediate uncinigers are excluded from the abdominal segment count. Branchial gap: width as number of branchial base, following Parapar et al. (2018). We excluded A. lindstroemi Malmgren, 1867 (part.) in Hessle, 1917 sensu Parapar et al. (2012) from this key, an undescribed species (Parapar et al., 2018), even though a brief diagnosis was given in Parapar et al. (2012).

1. Paleae stout basally (Figs 2, 3C)......................................................................... 2

- Paleae slender and evenly tapering to long filiform tips or absent (Figs 5A, 6A,B,D,E).............................. 5

2. Pygidium with one pair of short lateral lobes only; branchial gap absent; paleae gradually but quickly tapering to comparatively long filiform tips (rarely missing)............................. A. villenai Parapar, Helgason, Jirkov & Moreira, 2012

- Pygidium otherwise (with 2 long cirri and short papillae or with 2 short lateral lappets and a number of long anal cirri); paleae abruptly tapering to very short filiform tips (usually missing)................................................... 3

3. 2 intermediate uncinigers (IU) and 14–16 abdominal uncinigers (AU); prostomium with 2 small eyespots, branchial gap present (1); pygidium with 2 long cirri and a number of short papillae............................ A. goesi (Malmgren, 1865)

- 2 IU and 12 or less AU................................................................................ 4

4. Branchial gap present (1.5); 10 AU; pygidium with 2 short, wide lateral lappets and about 8 thin long anal cirri........................................................................................ A. acutifrons (Grube, 1860)

- Branchial gap absent or very narrow (<0.5); 11 (seldom 12) AU; pygidium with 2 long cirri and a number of small, round papillae; prostomium usually with 2 eyespots......................... A. finmarchica (Sars, 1865) sensu Holthe (1986)

5. Rudimental notopodia on 2 IU enlarged................................................................... 6

- All rudimental notopodia of similar size................................................................... 7

6. Gap between branchial groups as wide as width of group; 10 AU............................. A. falcata Eliason, 1955

- Gap between branchial groups narrower or absent; 22–26 AU................................. A. vega (Wirén, 1883)

7. Paleae at least twice as long or wide as the most developed notochaetae.......................................... 8

- Paleae fine, only slightly longer than the following notochaetae or absent....................................... 11

8. 2 IU and 10 AU with very long dorsal cirri (clearly longer than length of base of respective pinnule)........................................................................................... A. cirrata Webster & Benedict, 1887

- AU dorsal cirri (if present) short (less than half of length of base of respective pinnule)............................. 9

9. Pygidium with 2 long lateral cirri and several short papillae................................................... 10

- Pygidium otherwise (lateral cirri and long cirriform papillae almost same length)................................. 15

10. Pygidial cirri with a pair of eye spots, 10 AU.............. A. lindstroemi Malmgren in Hessle, 1917 sensu Holthe (1986)

- Pygidial cirri without eye spots, AU with short dorsal cirri.......................... A. santillani Parapar et al., 2018

11. Paleae absent; 12 thoracic uncinigers (TU); AU with long dorsal cirri; pygidium with 2 long cirri and a number of short cirriform papillae................................................................. A. petersenae Jirkov, 1997

- Paleae fine, only slightly longer than the following notochaetae............................................... 12

12. AU without dorsal cirri; branchial gap (1) or absent; 12 TU, 9 AU.............................................. 13

- AU with long dorsal cirri, at least as long as the base of respective pinnule; branchial gap (4); 11 TU, more than 9 AU.... 14

13. Branchial gap (1); prostomium and pygidial cirri with eyespots.......... A. oculicirrata Parapar, Moreira & Barnich, 2019

- Branchial gap absent; no prostomial or pygidial eyespots............ A. undecima Alvestad, Kongsrud & Kongshavn, 2014

14. 3 branchiae in each group arranged in a line, 4th branchia posterior to this row; IU with vestigial dorsal cirri; 10 AU........................................................................................ A. borealis (Sars, 1856)

- All 4 branchiae in each group arranged in a line; IU without dorsal cirri; 13–16 AU............ A. octocirrata (Sars, 1835)

15. AU with dorsal cirri in form of minute rounded lobe (often difficult to see), branchial gap present (≤1); small species, max. 11 mm long (or 18 mm; see Remarks).................................................... A. baltica Eliason, 1955

- AU with short dorsal cirri (easy to find), branchial gap present (1–3); large species, max. 80 mm long.................................................................................................. A. grubei Malmgren, 1865