Chaetozone monteverdii, 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 monteverdii sp. nov. Figures 9 , 10

Chaetozone sp. 1 Grosse et al. 2020: fig. 4.

Type locality.

Norwegian Sea, north-west of Bergen, 280 m depth.

Material examined.

Holotype: Norwegian Sea • 1 ind.; 61.37705°N, 2.11215°E; 31 May 2014; 280 m; ZMBN98250. Paratypes: North Sea • 1 ind.; 59.56729°N, 5.21568°E; 26 Apr. 2017; 328 m; ZMBN125786 • 1 ind.; 62.35117°N, 6.16178°E; 21 Jul. 2012; 243 m; ZMBN125783 • 1 ind.; 60.2593°N, 5.13703°E; 13 Jun. 2017; 248 m; ZMBN116562 • 2 ind.; 59.99°N, 5.35°E; 27 Jun. 2007; 250 m; NTNU-VM74506, ZMBN129648 .

Comparative material.

Chaetozone jubata : Paratypes: Faroe-Shetland channel • 2 ind.; 61.5.57°N, 2.4093°W; Jul. 1996; 710 m; NMSZ.1999.237.4-5.

Diagnosis.

Prostomium fused with peristomium, giving the anterior end a drop-like appearance; dorsal tentacles on segment 1 (achaetous), first pair of branchiae on segment 2 (achaetous); ventral ridge; long capillary chaetae on expanded anterior with fibrils arranged in distinctive transversal rows, numerous, long, broad and flat spines on high complete cinctures (Figs 9 , 10 ).

Molecular diagnosis.

COI: 97: G; 110: C; 145: C; 199: G; 232: 277: G; C; 281: G; 282:T; 356: C; 363: T, 459: T; 485: G, 515: A; 530: T; 564-565: CC, 37-38: TA. 28S: 58: A; 69: T; 440: A; 416-417: CT; 453-454: CT; 454-455: TG; 460-461: GC (based on ten COI sequences and 13 28S sequences).

Description.

A large species, holotype incomplete, 56 segments (51-56), 20 mm long (14-25 mm), 1.5 mm wide. (Fig. 9 ). Body elongate, larger anteriorly, narrowing towards the anterior end and in posterior half, oval to flattened oval in cross section anteriorly, round in cross section posteriorly. Anterior segments narrow and crowded, 5 or 6 × higher and wider than long, lengthening and enlarging progressively after first 10-15 segments to 2 × higher than long in posterior segments. Thin, shallow dorsal groove over first 10-15 segments. Prominent ventral ridge along anterior half of body.

Prostomium as long as peristomium, conical, blunt, fused with peristomium, without annulations; eyespots absent; nuchal organs simple slits on posterior margin of prostomium (Fig. 10A ). Peristomium short, as long as three segments, without annulations, overlapping segment 1 posteriorly, in large specimens much narrower than first segments giving whole head a characteristic "drop shape" clearly set off from rest of body (Fig. 10A ). Dorsal tentacles on segment 1 (achaetous), well separated (Fig. 10A ). Segment 1 achaetous, not completing dorsally, in large specimens, wider than peristomium but not as wide as segment 2 (achaetous) which can cover it on the side so that it is only "facing forward" (Fig. 10A ). First pair of branchiae arising from segment 2 (achaetous) (Fig. 10A ). Small dorsal crest over segments 1-4 in some specimens. Second pair of branchiae arising from chaetiger 1, dorsal to notopodia (Fig. 10A ). Subsequent branchiae similarly placed (Fig. 8A ). Branchiae or branchial scars present on most chaetigers until development of cinctures.

Parapodia as low mounds or ridges in anterior segments, progressively developing into elevated membranes and into complete cinctures around segment 38-43, with deep constrictions between the segments (Figs 9 , 10F ). 7-12 short capillary chaetae in anterior notopodia, approximately 12 in anterior neuropodia, smooth basally and with thin, dense fibrils along one edge from middle (Fig. 10C ). Approximately seven very long capillary chaetae in notopodia from chaetiger 3 or 4 up to chaetiger 25, segmented, each segment like a cylinder diagonally cut in cross section with thin fibrils along the edge, difficult to see with light microscopy but obvious with SEM (Fig. 10B, G ). 12-16 spines per neuropodia from segment 29-32, 12-14 per notopodia from segment 29-34, long, with a broad flattened elongated leaf shaped blade, slightly folded along its length, longer in notopodia, often crossing over dorsum (Fig. 10D, F ). Alternating capillary chaetae between all spines, as long or shorter than spines (Fig. 10D, F ).

Pygidium with terminal anus and with a small rounded ventral lobe (Fig. 10E ).

Etymology.

This species is named after Claudio Monteverdi, an Italian composer, author of the operatic scena 'Il combattimento di Tancredi e Clorinda’, amongst other pieces.

Methylene blue staining pattern.

No strong pattern. Some dark stained dots appear after differentiation on the pygidium, the posterior side of some parapodia, and the underside of some segments.

Remarks.

The size and volume of the prostomium, peristomium and the first segments varies in some specimens, which do not exhibit the characteristic “drop-shaped” head and enlarged anterior segments shown on Figures 9 , 10 , or sometimes only slightly. The prostomium and peristomium are, however, always fused and the arrangement of the dorsal tentacles and first pairs of branchiae is always the same, with dorsal tentacles on segment 1 (achaetous) and first pair of branchiae on segment 2 (achaetous).

This species is similar to C. jubata in the general appearance, presence of long chaetae (several times the body width) along the anterior part of the body (from approximately the 2nd-4th chaetigers to approximately the 25th for both species), and the distinctive ample posterior cinctures with big characteristic leaf shaped spines. Chaetozone jubata was described as having the tentacular palps originating dorsally from the posterior margin of the third peristomial ring. On the two paratypes of C. jubata examined, the peristomial rings are difficult to distinguish and there seems to be either a last, short peristomial ring or an achaetous segment between the tentacular palps and chaetiger 1, on which no branchiae was found. In Chaetozone monteverdii sp. nov. we interpret the tentacular palps as originating from a first achaetous segment, which is very distinct from the peristomium. Chaetozone monteverdii sp. nov. also differs from C. jubata in the nature of the long chaetae (segmented in C. monteverdii sp. nov.), the size of the specimens (up to 8 mm reported for C. jubata and 20 mm for C. monteverdii sp. nov.), the presence of a ventral ridge (a groove in C. jubata ) and the number of short capillary chaetae in anterior parapodia (5-10 in C. jubata and 19-24 in C. monteverdii sp. nov.). Chaetozone monteverdii sp. nov. is readily distinguished from most other species of Chaetozone in the area by the complete fusion of prostomium and peristomium and its distinctive drop-like head shape (in most specimens), the long capillary chaetae restricted to the anterior part of the body, and the amplitude of the posterior cinctures, along with the size and number of spines fully or nearly encircling them. However, it is very similar to Chaetozone sp. 2 and Chaetozone sp. 4 (in this paper), from which it is so far only distinguished by the nature of the long capillary chaetae, which present fibrils arranged in transversal rows unique to this species, and the presence of a ventral ridge instead of a ventral groove. Chaetozone monteverdii sp. nov., Chaetozone sp. 2, and Chaetozone sp. 4 are all found in the same geographic area (Norwegian coast and shelf) and in the same range of depths (~ 200-600 m).

Chaetozone monteverdii sp. nov. COI distance with other species in the area ranges from 22% to 26% (Table 2 ).

Distribution.

Norwegian coast and shelf, offshore and in the fjords, south of the Trondheimsfjord, ~ 200-300 m depth.

Figures

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.

Figure 9. Chaetozone monteverdii sp. nov., Holotype ZMBN 98250 in lateral view.

Figure 10. Chaetozone monteverdii sp. nov. A paratype ZMBN 125786, SEM of anterior end in lateral view B paratype ZMBN 125786, SEM of long segmented notopodial capillary C paratype ZMBN 125786, SEM of smooth notopodial capillary D paratype ZMBN 129648, SEM of notopodial spine E paratype ZMBN 129648, SEM of pygidium in lateral view F paratype ZMBN 116562, cross section of posterior segment G paratype ZMBN 129648, SEM of long segmented notopodial capillary. Abbreviations: br, branchiae; Ch, chaetiger; dT, dorsal tentacles; nuO, nuchal organ; per, peristomium; pr, prostomium; Seg, segment.