Chaetozone chambersae, 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 chambersae sp. nov. Figure 11

Chaetozone sp. 12 Grosse et al. 2020: fig. 4.

Material examined.

Holotype: North Sea • 1 ind.; 58.274250°N, 2.644216°W; 18 Jul. 2008; 56 m; NTNU-VM74546 . Paratypes: North Sea • 3 ind.; 51.354333°N, 2.796667°E; 14 Sep. 2010; 22 m; NTNU-VM74486-74487, ZMBN129642 • 1 ind.; 57.777177°N, 2.905357°W; 17 Jul. 2008; 37 m; NTNU-VM74537 • 1 ind.; 51.352833°N, 2.862°E; 14 Sep. 2010; 18.9 m; NTNU-VM74483 • 1 ind.; 51.3575°N, 2.8041°E; 14 Sep. 2010; 21.5 m; NTNU-VM74485 .

Comparative material.

Chaetozone christiei : Holotype: North Sea • 1 ind.; Nov. 1982; 55.32°N, 1.36°W; NMSZ.1998. 122 . Paratypes: North Sea • 2 ind .; Nov. 1982; 55.32°N, - 1.36°W; NMSZ.1998.123.

Diagnosis.

Dorsal and ventral grooves along the body; paired tentacles on the posterior margin of the peristomium; first branchiae between peristomium and first chaetiger, beside tentacles; capillary chaetae short and thick; 13-16 spines per parapodia in posterior segments (Fig. 11 ).

Molecular diagnosis.

COI: 163: C; 517: G; 512-513: GG. 28S: 89: C; 638: T (based on 17 COI sequences and 10 28S sequences).

Description.

A medium species, holotype complete, 124 segments (84-129), 10 mm long (7.5-14) (Fig. 11E ). Colour in ethanol white to light tan. Body elongate, narrowing anteriorly and posteriorly, round in cross section, dorsum and venter rounded. Anterior and midbody segments 5-6 × wider than long. Posterior segments 1.5 × wider than long. Thin, shallow dorsal groove along most of body. Faint to distinct ventral groove along most of body.

Prostomium long like two third of peristomium, conical, blunt; eyespots absent; nuchal organs simple slits at posterior margin of prostomium. Peristomium as long as four or five segments, rarely with two distinct annulations, of approximately equal size, partially fused with chaetiger 1 posteriorly. Dorsal tentacles arising from the posterior margin of peristomium, well separated (Fig. 11B, C ). First pair of branchiae arising between peristomium and chaetiger 1, just beside dorsal tentacles (Fig. 11B, C ). Second pair of branchiae arising from posterior margin of chaetiger 1, dorsal to notochaetae (Fig. 11B ). Subsequent chaetigers with branchiae similarly placed. Branchiae or branchial scars present on most chaetigers until development of cinctures.

Parapodia as low mounds or ridges in anterior and middle segments, progressively developing posteriorly into elevated membranes and into incomplete cinctures around segment 90, arising laterally and dorsally, not developing ventrally (Fig. 11A, D ). Approximately 20 capillary chaetae per anterior parapodia, short, smooth, thick, and sometimes darkly pigmented in anterior chaetigers (Fig. 11C ). Seven or eight spines per neuropodia from segment 43-60, 6-8 in spines per notopodia from segment 46-67, short, unidentate, pointy, slightly curved, transparent (Fig. 11A, D ). Alternating capillaries between most spines, rarely two between two spines, thin, up to three times longer than the spines in notopodia (Fig. 11A, D ).

Pygidium with terminal anus and with a small triangular ventral lobe.

Etymology.

This species is named after Dr Susan Chambers, for her work on European cirratulids.

Remarks.

This species is similar to C. christiei in general appearance and in having low, incomplete cinctures with short spines, although it has a few more spines per parapodia than C. christiei . Chaetozone chambersae sp. nov. differs from C. christiei in the position of the first pair of branchiae, which are on the posterior margin of the peristomium, beside the tentacular palps, rather than on the first chaetiger. Chaetozone chambersae sp. nov. differs from C. setosa notably in the absence of a first achaetous segment and fewer, shorter spines.

Chaetozone chambersae sp. nov. is found in British waters, from where many European Cirratulidae species are described. Particular care should be used when identifying cirratulids from this area because of the presence of several undescribed species ( Christie 1985; Chambers 2000), the presence of variability in the type material of some species (e.g., C. christiei ) and the revelation of a much higher diversity that expected in this group ( Grosse et al. 2020). It will be important to get better understanding of the British fauna using DNA-based methods.

Chaetozone chambersae sp. nov. COI distance with other species in the area generally ranges from 18% to 25% with a minimum at 10% with Chaetozone sp. 11 (Table 2 ).

Distribution.

North Sea, northeast of Scotland, and off Belgium, from ~ 20 to 60 m depth.

Figures

Figure 11. Chaetozone chambersae sp. nov. A paratype ZMBN 129642, SEM of posterior neuropodia B paratype ZMBN 129642, SEM of anterior end in dorso- lateral view C paratype NTNU-VM 74486, anterior end in lateral view D paratype D NTNU-VM 74487, cross section of posterior parapodia E holotype NTNU-VM 74546 in dorso-lateral view. Abbreviations: br, branchiae; Ch, chaetiger; dT, dorsal tentacles; nuO, nuchal organ; per, peristomium; pr, prostomium; Seg, segment.