Ampharete, Malmgren, 1865

Krüger, Lotte, Dietrich, Anna, Bastrop, Ralf & Bick, Andreas, 2022, From synonym to valid species: Redescriptions of Ampharete acutifrons (Grube, 1860) and A. cirrata Webster & Benedict, 1887, and brief descriptions of A. baltica Eliason, 1955 and A. grubei Malmgren, 1865 (Annelida: Terebellida: Ampharetidae), Zootaxa 5174 (4), pp. 357-380 : 376-377

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

Figures

FIGURE 2. Original drawings from the first description of Amphicteis acutifrons by Grube 1860. 6. Anterior end, ventral view. 6a. Posterior end with anal cirri, ventral view.

FIGURE 3. Ampharete acutifrons. Holotype (ZMB Verm. 1575), Micrographs of methyl blue staining pattern. A. Complete specimen, ventral view, with continuous ventral shields from segment I to XIV and median ventral groove from segment XV to posterior end. B. Dorsal view on posterior thorax and abdomen with damaged segments.Arrows point towards eggs, leaving the body wall in intermediate and following three abdominal segments. Note:Abdominal neuropodia without cirri. C. Anterior end, dorsal view with branchiae missing, bases still recognizable. Note: Presence of thick and relatively short paleae and two buccal tentacles. D. Dorsal view on paleae of left body side in detail. Arrow indicates smaller and thinner paleae. E. Posterior end with anal cirri. F. Thoracic notopodia 6-9, dorsal view. G. Last thoracic notopodium with differing diameters of chaetae. H. Detached abdominal uncinus. Scale bars: A, B = 500 µm. C = 400 µm. D, E = 200 µm. F = 100 µm. G = 75 µm, H = 10 µm.

FIGURE 5. Ampharete cirrata. A. Anterior end, dorsal view with dissected branchiae. Arrow is pointing towards nephridial papilla on segment IV. B. Last thoracic, intermediate and first abdominal segments (segments XVII–XX), lateral view. Arrow is pointing towards papilla (glandular pad?) above the neuropodium. C. Differing shapes of abdominal pinnules with cirri, last pinnule (rightmost) always elongated (two-sided arrow indicates length of base of pinnule). D. Thoracic and intermediate uncini. E. Abdominal uncinus. Scale bars: A, B = 200 µm. C = 100 µm. D, E = 10 µm.

FIGURE 6. Ampharete cirrata, SEM micrographs.A. Anterior end, ventral view with buccal tentacles. B. Anterior end, frontal view. C. Buccal tentacles from A, enlarged. D. Paleae from B, enlarged. E. Anterior end, dorsal view with one branchia.Arrows are pointing towards nephridial papillae on segment IV. F. Posterior end, terminal view on anal cirri. G. Posterior end, lateral view, with abdominal pinnules with dorsal cirri and anal cirri. Scale bars: A, B, E, G = 200 µm. C, D = 50 µm. F = 100 µm.