Chaetozone pseudosetosa, Grosse & Capa & Bakken, 2021

Grosse, Mael, Capa, Maria & Bakken, Torkild, 2021, Describing the hidden species diversity of Chaetozone (Annelida, Cirratulidae) in the Norwegian Sea using morphological and molecular diagnostics, ZooKeys 1039, pp. 139-176 : 139

Chaetozone pseudosetosa sp. nov. Figures 5 , 6

Chaetozone sp. 7 Grosse et al. 2020: fig. 4.

Type locality.

Drøbak, Oslofjorden, south of Storskjær, Norway, 31 m depth.

Material examined.

Holotype: Oslofjorden , Norway • 59.6562°N, 10.6081°E; 20 Oct. 2014; 31 m; ZMBN125756 . Paratypes: Oslofjorden , Norway • 3 ind.; 59.6444°N, 10.6192°E; 21 Oct. 2014; 106 m ; NTNU- VM74516-74518 • 1 ind.; 59.05485°N, 10.250467°E; 29 May 2011; 70 m; NTNU-VM74514 • 1 ind.; 59.89017°N, 10.75551°E; 20 Sep. 2018; 12 m; NTNU-VM76534 • 1 ind.; 59.89731°N, 10.73703°E; 20 Sep. 2018; 8 m; NTNU-VM76547. - North Sea • 1 ind.; 59.28789°N, 5.32506°E; 08 Jun. 2014; 76 m ; ZMBN125790 • 1 ind.; 59.02985°N, 5.44881°E; 10 Jun. 2014; 59 m; ZMBN125789 • 3 ind.; 60.269686°N, 5.197750°E; 26 Jul. 2014; 120 m; NTNU-VM74525-74526, 74528 • 1 ind.; 59.76022°N, 5.49682°E; 08 Jun. 2014; 40 m; ZMBN125787 • 1 ind.; 60.90389°N, 7.16813°E; 17 Nov. 2012; 115 m; ZMBN125795 • 1 ind.; 58.24753°N, 6.53673°E; 03 Feb. 2016; 155 m; ZMBN125824 • 1 ind.; 60.60332°N, 5.09513°E; 6 Mar. 2017; 94 m; ZMBN125780. - Norwegian Sea • 1 ind.; 63.44753°N, 10.62730°E; 07 Feb. 2018; 77 m ; NTNU-VM74602 • 1 ind.; 63.437891°N, 10.50624°E; 04 Sep. 2018; 4 m; NTNU-VM75900. - Barents Sea • 1 ind.; 70.262°N, 31.083833°E; 16 Apr. 2014; 126 m ; NTNU-VM74499. - Sweden • 2 ind.; 58.866667°N, 11.1°E; 2005; 70 m ; ZMBN129641, 129647 • 2 ind.; 58.8°N, 11.1°E; Nov. 2018; 60 m; ZMBN129643, ZMBN129644.

Diagnosis.

Peristomium with two large distinct annulations and dorsal crest; paired tentacles on posterior margin of peristomium; first branchiae on distinct segment 1 (achaetous); posterior segments developed in full cinctures with up to 20-26 spines per parapodia (Figs 5 , 6 ).

Molecular diagnosis.

COI: 223: C; 471-472: CA; 349-350: TT (based on 45 COI sequences).

Description.

A medium to large species, holotype incomplete, with 78 segments (70-106), 16.5 mm long (12-20 mm), up to 1.2 mm wide (Fig. 5 ). Colour in ethanol white to light tan. Body elongate, wider in midbody segments, narrowing anteriorly and posteriorly; circular to oval in cross section. Anterior first 15-20 segments 5-6 × wider than long, progressively lengthening 3 × longer posteriorly (Fig. 5 ). Thin, shallow dorsal groove from segment 10-15. Distinct ventral groove along most of body (Fig. 5 ).

Prostomium short, long as two third of peristomium, conical to triangular, tapering to rounded anterior tip, without annulations; eyespots absent; nuchal organs as narrow slits at posterior margin of prostomium (Fig. 6A, B ). Peristomium as long as wide, with two large rings of similar length, distinct laterally, weakly distinct or invisible dorsally on dorsal crest; dorsal crest little to well developed, covering all peristomium, slightly overlapping prostomium anteriorly, extending posteriorly between dorsal tentacles, up to anterior margin of chaetiger 1 (Fig. 6A, B ). Dorsal tentacles arising from posterior margin of peristomium, well separated (Fig. 6A, B ). First pair of branchiae arising from segment 1 (achaetous), posterior to dorsal tentacles (Fig. 6A, B ). Second pair of branchiae arising from chaetiger 1, dorsally and slightly posterior to notopodia. Subsequent branchiae similarly placed. Branchiae or branchial scars on most chaetigers until development of cinctures.

Parapodia as low mounds or ridges in anterior and middle segments, progressively developing into high, elevated membranes and into complete cinctures from segment 63 (50-85) (Figs 5 , 6C, F ). 6-11 short capillaries per neuro- and notopodia throughout, smooth; 2-4 long natatory-like capillaries per notopodia from segment 20 or 21 to 70-72, up to 1.5 × longer than body width, smooth (Fig. 6E ). 8-13 spines per neuro- and notopodia, from segment 42-54 in neuropodia and segment 46-54 in notopodia, unidentate, sigmoid, rarely slightly crossing dorsally in posterior cinctures (Fig. 6C, D, F ). Alternating capillaries usually between all spines, of similar length of longer than spines.

Pygidium with terminal anus and with small rounded ventral lobe (Fig. 6G ).

Methylene blue staining pattern.

A moderately distinctive pattern. Methyl blue stains the peristomium lightly in transversal bands. Dorsum does not stain. Transversal lines of dark blue dots are present along anterior segments, more or less dense but never strong, not covering the whole length of the segments, creating a light stripe pattern anteriorly. Rows of dark blue dots also present on most mid and posterior parapodia, not conspicuous and only lateral in midbody segments.

Etymology.

This species is named Chaetozone pseudosetosa because it looks identical to C. setosa and has been identified as such until now.

Remarks.

Although this species is morphologically indistinguishable from C. setosa , it is a distinct species, and thus we felt it was important to name it. Cryptic species are important to take into account ( Nygren 2014), which is difficult to do if they are not named, do not have a type, and are not diagnosed either morphologically or molecularly. In the absence of diagnostic morphological characters to distinguish it from C. setosa , molecular diagnostic characters can be of help ( Nygren and Pleijel 2011; Parapar et al. 2020). In particular, C. setosa is known as a bioindicator and distinguishing between C. setosa and C. pseudosetosa sp. nov. can be important in that regard.

Chaetozone pseudosetosa sp. nov. COI distance with other species in the area mostly ranges from 20% to 25%, with a minimum of 8% with Chaetozone setosa (Table 2 ).

Distribution.

Norwegian coast and shelf, Skagerrak, North Sea, 4-160 m depth. One specimen is recorded from Finnmark, which means it may be sympatric with C. setosa in this area.

Figures

Figure 5. Chaetozone pseudosetosa sp. nov., holotype ZMBN 125756 A holotype in ventral view, stained with Shirlastain A B holotype in dorsal view, stained with Shirlastain A. Abbreviations: br, branchiae; dGr, dorsal groove; per, peristomium; vGr, ventral groove; a star (*) indicates where parapodia were removed for DNA analyses.

Figure 6. Chaetozone pseudosetosa sp. nov. A paratype ZMBN 125780, SEM of anterior end in lateral view B paratype ZMBN 129644, SEM of anterior end in dorsal view C paratype NTNU-VM 74602, cross section of posterior segment D paratype ZMBN 125780, SEM neuropodial spines E paratype ZMBN 129644, SEM of notopodial capillary F Paratype ZMBN 129644, SEM of posterior neuropodia G paratype ZMBN 129643, SEM of pygidium. Abbreviations: br, branchiae; Ch, chaetiger; dCr, dorsal crest; dT, dorsal tentacle; nuO, nuchal organ; per, peristomium; pr, prostomium; pyg, pygidium; Seg, segment.