Chaetozone quinta, 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 quinta sp. nov. Figure 7

Chaetozone sp. 5 Grosse et al. 2020: fig. 4.

Type locality.

Søra Kjerringasundet, east of Sotra, Bergen, 75 m depth.

Material examined.

Holotype: North Sea • 1 ind.; 60.32652°N, 5.14085°E; 02 Sep. 2014; 75 m; ZMBN125802 . Paratypes: North Sea • 1 ind.; 61.04889°N, 4.9723°E; 15 Jul. 2015; 161 m; ZMBN125777 • 1 ind.; 60.50728°N, 5.00028°E; 30 Nov. 2015; 66 m; ZMBN125807 . Other material examined. North Sea • 3 ind.; 60.355133°N, 5.168967°E; 10 Apr. 2018; 92 m; ZMBN138610-138612 .

Diagnosis.

Prostomium ventrally bi-annulated; peristomium short and without annulations; wide ventral groove; paired tentacles and first branchiae on segment 1 (achaetous); posterior segments developed in incomplete cinctures bearing 9-11 spines per parapodia (Fig. 7 ).

Molecular diagnosis.

COI: 446: T; 475: G; 539: T; 548: T; 607: G; 349-350: GG; 361-362: AG; 486-487: TA (based on 2 COI sequences).

Description.

A medium species, holotype incomplete, 61-70 segments, 6-8 mm long, 0.6-1 mm wide. Colour of ethanol preserved specimens white to light tan. Body elongate, narrowing progressively anteriorly, 2-3 × wider at anterior third than at anterior end. Round in cross section anteriorly, widening progressively to a flatten oval at anterior third. Anterior segments 5 × higher and wider than long. Midbody segments 10 × wider and 5 × higher than long. Posterior segments 2.5 × higher and 3 × wider than long. Thin shallow dorsal groove, best visible anteriorly. Wide shallow ventral groove along entire body (Fig. 7C ).

Prostomium longer than peristomium, conical, tapering to rounded anterior tip; with ventrally and laterally distinct posterior annulation above mouth, as long as segment 1; eyespots absent; nuchal organs simple slits at posterior margin of prostomium, above posterior annulation (Fig. 7A ). Peristomium short, as long as segment 1 ventrally, as long as two segments dorsally, without annulations, overlapping with prostomium anteriorly (Fig. 7A ). Dorsal tentacles arising from segment 1 (achaetous), well separated (Fig. 7A ). First pair of branchiae arising from segment 1, immediately behind tentacles (Fig. 7A ). Segment 1 longer than chaetiger 1, achaetous, weekly bi-annulated (Fig. 7A ). Second pair of branchiae arising from chaetiger 1, dorsal and slightly posterior to parapodia (Fig. 5A ). 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 segments, developing into relatively low incomplete cinctures from segment 45-50, arising on each side but not completing over venter and dorsum. Five or six short capillaries in neuropodia throughout, in notopodia from development of spines, smooth; 5-7 medium capillaries in notopodia, from chaetigers 1-29, twice as long as neuropodial capillaries, smooth; one or two long capillaries in notopodia from segment 12 to 27-29, smooth (Fig. 7D ). Five or six spines per neuropodia from segment 27-29, four or five spines per notopodia from segments 31 or 32, unidentate, short, rather spread out (Fig. 7B ). Alternating capillaries between most spines except ventralmost, slightly longer than spines.

Pygidium with terminal anus and with a short, rounded ventral lobe.

Methylene blue staining pattern.

Prostomium except tip, peristomium and sides of segment 1 retain a dark blue stain, while rest of body does not stain.

Etymology.

Quinta is the cardinal adjective for fifth in the feminine nominative singular, as this species has always been " Chaetozone sp. 5". It is also named with a thought for a friend and colleague who is named after the same number.

Remarks.

This species is easily distinguished from other species of Chaetozone in Norwegian waters by its distinct bi-annulated prostomium, short peristomium, and segment 1 (achaetous) bearing both tentacles and first branchiae. For other species of Chaetozone in the area, prostomium is always simple. The methylene blue staining pattern is also unique and easily recognisable, with most of prostomium except the distal tip, peristomium and sides of segment 1 retaining a dark blue pattern, unlike the rest of the body.

Chaetozone quinta sp. nov. COI distance with other species in the area mostly ranges from 23% to 28%, with a minimum of 9% with Chaetozone sp. 4 (Table 2 ).

Distribution.

Norwegian coast and shelf, ~ 60-160 m depth.

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 7. Chaetozone quinta sp. nov. A ZMBN 138610, anterior end in lateral view, stained with Shirlastain A B paratype ZMBN 125807, SEM of neuropodial spine C holotype ZMBN 125802 in lateral view, stained with Shirlastain A D paratype ZMBN 125807, SEM of capillary chaetae. Abbreviations: br, branchiae; Ch, chaetiger; dT, dorsal tentacles; mo, mouth; nuO, nuchal organ; per, peristomium; pr, prostomium; Seg, segment; vGr, ventral groove.