Chaetozone cf. zetlandica McIntosh, 1911

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 cf. zetlandica McIntosh, 1911 Figures 12 , 13

Chaetozone zetlandica McIntosh, 1911: 171; Southern, 1914: 115, pls 12, 13, fig. 29A-K.

Caulleriella zetlandica : Day, 1967: 507; Woodham and Chambers 1994: 311 figs 2, 4.

Heterocirrus zetlandica : Fauvel 1927: 99, fig. 34i-n.

Chaetozone sp. 10 Grosse et al. 2020: fig. 4.

Material examined.

Norwegian Sea • 1 ind.; 60.54973°N, 5.22897°E; 20 Apr. 2017; 37 m; ZMBN125779 • 2 ind.; 60.17295°N, 5.00315°E; 24 Apr. 2014; 6 m; ZMBN125819-125820 • 1 ind.; 60.51035°N, 5.19158°E; 30 Nov. 2015; 32 m; ZMBN125808 • 1 ind.; 60.173°N, 5.003°E; 23 Apr. 2014; 6 m; ZMBN95386 • 1 ind.; 63.43206°N, 10.37709°E; 07 Sep. 2018; 5 m; NTNU-VM76410 • 1 ind.; 59.97547°N, 5.73998°E; 19 Sep. 2018; 10 m NTNU-VM76478 • 1 ind.; 60.3188833°N, 5.2552833°E; 12 Sep. 2019; 48 m; NTNU-VM76407 • 1 ind.; 60.39426°N, 5.30989°E; 10 Sep. 2018; 4.5 m; NTNU-VM76409.

Comparative material.

Chaetozone zetlandica : Holotype: Shetland • 1 ind.; Jul. 1867; 170 m; BMNH 1921.5.1.3232.

Diagnosis.

All segments narrow, of approximately the same length; red eyespots; peristomium dorsally rounded; paired tentacle on incomplete segment 1 (achaetous); first branchiae on segment 1 (achaetous); posterior end flattened, posterior chaetigers with low, incomplete cinctures (Figs 12 , 13 ).

Molecular diagnosis.

28S: 636: T; 675: T (based on 9 COI sequences and 4 28S sequences).

Description.

A large species, 130-154 segments, up to 22 mm long, 3 mm wide, 2 mm high. Body elongate, slightly widening after the middle before narrowing and flattening in posterior quarter, round-oval in cross section anteriorly. Anterior and midbody segments approximately all the same length, all very short, approximately 10 × higher than long, lengthening progressively to 6 × wider than long in posterior segments. Thin dorsal groove in midbody; large ventral groove (Figs 12 , 13E ).

Prostomium short, one third of peristomium, conical, blunt, without annulations; red eyespots around the nuchal organs; nuchal organs simple slits at posterior margin of prostomium (Fig. 13B ). Peristomium short, long as five segments, higher than long, dorsum rounded, two annulations of approximately equal length, second one shorter ventrally and extending dorsally posteriorly between dorsal tentacles (Fig. 13B ). Dorsal tentacles arising from segment 1 (achaetous), clearly separated (Fig. 13A, B ). First pair of branchiae beside or directly posterior to paired tentacles, on segment 1 (achaetous) (Fig. 13A, B ). Second pair of branchiae on chaetiger 1, just above notopodia. Subsequent branchiae similarly placed. Branchiae or branchial scars on all chaetigers including posterior cinctures.

Parapodia as low mounds or ridges in anterior and midbody chaetigers, progressively developing into elevated membrane and into incomplete cinctures around segment 120, encircling only the sides of posterior segments (Figs 12 , 13C, E-G ). 11-15 Smooth short thick capillary chaetae in neuropodia in anterior and midbody chaetigers, in notopodia along entire body, arranged in two rows in anterior segments (Fig. 13A, D ). Smooth short thin chaetae in neuropodia and notopodia in midbody and posterior segments, alternating with thick capillaries in midbody segments, alternating with spines in posterior segments. 7-10 pointed acicular spines in posterior neuropodia from segment 100 (Fig. 13C, F ). 7-9 long capillary tipped spines in posterior notopodia from segment 110 (Fig. 13F ). Alternating capillaries between all spines (Fig. 13F ).

Pygidium with terminal anus, long, cylindrical, with a short ventral lobe and dorsal mound overlapping last two chaetigers (Fig. 13G ).

Methylene blue stain.

No particular pattern. Prostomium and peristomium stain a bit darker than rest of body, except for a band joining nuchal organs dorsally, and dorsum barely shows any stain.

Remarks.

The specimens examined resemble the fragment of the holotype of Chaetozone zetlandica . Chaetozone zetlandica was described from a unique posterior fragment that is in poor condition and lacks most chaetae. One neuropodium is complete and shows unidentate spines arranged in a distinct armature on an elevated membrane. Nothing could be seen from the notopodia. Southern (1914) described a number of complete specimens from Scotland he identified as C. zetlandica based on the original fragment from McIntosh (1911). Woodham and Chambers (1994) also examined material from Scotland that they attributed to this species but placed it in the genus Caulleriella . They formed this new combination because they did not see any spines in the notopodia and observed some bidentate spines in the neuropodia of small specimens. They did show, however, what they called “awl-shaped” capillary chaetae, as thick as the acicular spines, but longer, and indeed terminating into thin capillary instead of having a blunt tip. These “awl-shaped” capillary chaetae are also shown arranged in a distinct armature, with alternating capillary chaetae on an elevated membrane. As Blake (2018) states, the chaetae of Caulleriella are not arranged in cinctures and as the “awl-shaped” capillary chaetae of this species might indeed just be spines, Caulleriella zetlandica is strongly suspected to be Chaetozone zetlandica . Woodham and Chambers (1994) provided a detailed redescription from a quantity of specimens they also compared to the fragment holotype. Specimens examined in our study mostly confirm to their description. Where they describe the dorsal tentacles as arising from a third peristomial annulation, we describe the dorsal tentacles of our material as arising from segment 1 (achaetous), which is a difference in interpretation rather than a difference in morphology. Woodham and Chambers also describe the first pair of branchiae as arising from the first chaetiger, but their SEM pictures show that it either arise at the anterior of this chaetiger (in addition to a second pair placed posteriorly on the same chaetiger), or from the third peristomial annulation. This last interpretation would be similar to the description we make of our material. However, this possible variation in the position of branchiae cannot be confirmed until more specimens are available.

The specimens described herein are also very similar to Chaetozone sp. 9 from Grosse et al. (2020), a species not described here as only two specimens were available. New observations from ongoing work indicate a third genetic clade in this complex. Either of these lineages could be C. zetlandica . This is why the species described here as Chaetozone sp. 10 is referred with reservations. Although available descriptions in the literature are detailed ( Southern 1914; Woodham and Chambers 1994), results presented here show the presence of putative cryptic species that at present cannot with certainty be attributed to the name McIntosh (1911) had available specimens for his original description. We suggest this is solved by examining specimens representing all genetic lineages and assigning the name C. zetlandica to one of them. Moreover, due to the condition of the holotype and the un-informativeness of the original description, the validity of the name Chaetozone zetlandica may need to be re-assessed in the future.

The COI distance between Chaetozone cf. zetlandica and Chaetozone sp. 9 is 10% (Table 2 ). COI distances with other species in the area vary between 19% and 26% (Table 2 ).

Distribution.

Norwegian coast and shelf, ~ 5-40 m depth.

Figures

Figure 12. Chaetozone cf. zetlandica. NTNU-VM 76410 in dorso-lateral view, stained with Shirlastain A. Abbreviations: per, peristomium; pr, prostomium; pyg, pygidium; vGr, ventral groove; an asterisk (*) indicates where the parapodia were removed for DNA analyses.

Figure 13. Chaetozone cf. zetlandica A ZMBN 125808, SEM of dorsal tentacle and first branchiae B ZMBN 125808, SEM of anterior end in lateral view C ZMBN 125808, SEM of neuropodial posterior spines D ZMBN 125808, SEM of anterior parapodia and capillary chaetae E ZMBN 125820 in lateral view, stained with Shirlastain A F ZMBN 95386, cross section of posterior parapodia G NTNU-VM 76410, pygidium in lateral view, stained with Shirlastain A. Abbreviations: br, branchiae; Ch, chaetiger; dT, dorsal tentacles; nuO, nuchal organ; per, peristomium; pr, prostomium; Seg, segment.