Chaetozone barentsensis, 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 barentsensis sp. nov. Figure 8

Chaetozone sp. 3 Grosse et al. 2020: fig. 4.

Type locality.

Barents Sea, 337 m depth.

Material examined.

Holotype: Barents Sea • 1 ind.; 71.056°N, 29.655667°E; 21 Apr. 2014; 337 m; NTNU-VM74492. Paratypes: Barents Sea • 7 ind.; 71.056°N, 29.655667°E; 21 Apr. 2014; 337 m; NTNU-VM74493-74498, ZMBN129638 • 2 ind.; 71.187833°N, 28.943167°E; 23 Apr. 2014; 380 m; NTNU-VM74489, ZMBN129639. - North Sea • 1 ind.; 60.173°N, 5.003°E; 22 Apr. 2011; 6 m; ZMBN95707 .

Diagnosis.

Dorsal tentacles on distinct segment 1 (achaetous); first branchiae on indistinct segment 2 (achaetous); approximately 22 short, flat spines per parapodia in posterior segments (Fig. 8 ).

Molecular diagnosis.

COI: 158: A; 214: G; 518: A; 283-284: CT; 289-290: TA. 28S: 37: A; 419: T; 457: A; 461: A; 462: A; 510: C (based on 13 COI sequences and 3 28S sequences).

Description.

A small species, holotype complete, 40-48 segments, 4-5 mm long, 0.25 mm wide (Fig. 8A ). Colour in ethanol white to light grey. Body elongate, without any distinct enlargement, rather round in cross section, slightly flattened in posterior half. Anterior segments 4 × higher than long. Posterior segments 2 × higher than long. Dorsal groove over posterior half. Ventral ridge along entire body.

Prostomium as long as peristomium, 2 × longer than high, conical, without annulations; eyespots absent; nuchal organs simple slits at posterior margin of prostomium (Fig. 8B ). Peristomium short, as long as two anterior segments, sometimes appears partially divided in two annulations, one anterior to mouth and one bearing mouth (Fig. 8B ). Dorsal tentacle arising from segment 1 (achaetous), well separated. Segment 1 achaetous, distinct from peristomium (Fig. 8B ). First pair of branchiae arising from segment 2 (achaetous), aligned with dorsal tentacles and second pair of branchiae (Fig. 8B ). Segment 2 achaetous, often indistinct from segment 1 and chaetiger 1 (Fig. 8B ). Second pair of branchiae arising from chaetiger 1, dorsal to notopodia (Fig. 8B ). Subsequent 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 parts, progressively developing into elevated membrane and into complete cinctures around segment 25-37 (Fig. 8A ). Thirteen smooth short capillary chaetae present in all chaetigers 2-4 long chaetae in anterior notopodia, up to several times body width. 22 spines from segment 24-28 in neuropodia and segment 25-29 in notopodia, short, slightly curved, dorsalmost spines thin and rounded in cross section, gradually flattening and widening towards most lateral positions (Fig. 8C ). Alternating capillaries present between all spines, longer than spines (Fig. 6C ).

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

Methylene blue staining pattern.

No particular pattern. Prostomium and peristomium retains slightly more stain than rest of body.

Etymology.

The name comes from the Barents Sea, where the species was found.

Remarks.

Chaetozone barentsensis sp. nov. is similar in general appearance to C. setosa , which is found in the same area, although it is smaller (up to 5 mm vs. 3 cm for C. setosa ) and differs, in particular, in the position of its tentacles which arise from the first achaetous segment vs. posterior margin of the peristomium for C. setosa , the presence of a ventral ridge instead of a groove, and the shape of its spines which are significantly shorter than that of C. setosa .

Chaetozone barentsensis sp. nov. COI distance with other species in the area mostly ranges from 23% to 26%, with a minimum of 9% with Chaetozone sp. 14 (Table 2 ).

Distribution.

Chaetozone barentsensis sp. nov. is found in the Barents Sea, ~ 400 m depth. One specimen was found on the Norwegian coast outside Bergen at 6 m depth.

Figures

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.

Figure 8. Chaetozone barentsensis sp. nov. A holotype NTNU-VM 74492 in lateral view, stained with Shirlastain A B paratype ZMBN 129638, SEM of anterior end in lateral view C paratype ZMBN 129639, SEM of posterior notopodia. Abbreviations: br, branchiae; Ch, chaetiger; dT, dorsal tentacles; per, peristomium; pr, prostomium; Seg, segment.