Raricirrus arcticus Buzhinskaja & Smirnov 2017
Creators: name: Grosse, Maël
name: Kongsrud, Jon Anders
name: Alvestad, Tom
name: Eilertsen, Mari Heggernes
name: Budaeva, Nataliya
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Annelida
Polychaeta
Terebellida
Cirratulidae
Raricirrus
Raricirrus arcticus

description: Raricirrus arcticus Buzhinskaja & Smirnov, 2017
Figs 8–9
Diagnosis
Heart body from chaetiger 2; branchiae cylindrical; distinct ciliary field near mouth; long serrate chaetae with straight tips in midbody neuropodia.
Material examined
ARCTIC MID-OCEAN RIDGE • 1 spec.; Loki’s Castle hydrothermal vent field; 73.5662° N, 8.1585° E; 2300 m depth; 14 Jul. 2008; collected with ROV; sample BIODEEP08-LC-ROV11; fixed in 96% ethanol; DNA voucher: LC06; ZMBN 157600 • 5 specs; same data as for preceding; ZMBN 157689 • 3 specs; Loki’s Castle hydrothermal vent field; 73.5662° N, 8.1583° E; 2330 m depth; 15 Jul. 2008; collected with ROV; sample BIODEEP08-LC-ROV12; fixed in 96% ethanol; ZMBN 157601 • 17 specs; Loki’s Castle hydrothermal vent field, barite field; 74.5661° N, 8.1585° E; 2357 m depth; 7 Aug. 2009; collected with ROV; sample H2 DEEP09 -ROV08; fixed in 96% ethanol; ZMBN 157686 • 72 specs; same data as for preceding; ZMBN 157602 • 1 spec.; same data as for preceding; DNA-voucher: LC08; ZMBN 157621 • 1 spec.; same data as for preceding; DNA-voucher: LC09; ZMBN 157687 • 4 specs; same data as for preceding; ZMBN 157688 • 1 spec.; same data as for preceding; ZMBN 157604 • 5 specs; same data as for preceding; ZMBN 157610 • 1 spec.; same data as for preceding; ZMBN 157605 • 2 specs; same data as for preceding; mounted on SEM-stub; ZMBN 157685 • 1 spec.; same data as for preceding; ZMBN 157603 • 1 spec.; Loki’s Castle hydrothermal vent field, barite field; 73.5665° N, 8.1618° E; 2385 m depth; 15 Jul. 2010; collected with ROV; sample GS10-ROV04; fixed in 96% ethanol; DNA-voucher: LC07; ZMBN 157509 • 1 spec.; same data as for preceding; DNA-voucher: LC10; ZMBN 157510 • 1 spec.; same data as for preceding; DNA-voucher: LC11; ZMBN 157511 • 24 specs; same data as for preceding; ZMBN 157606 • 28 specs; same data as for preceding; ZMBN 157607 • 46 specs; same data as for preceding; fixed in formaldehyde and transferred to 75% ethanol; ZMBN 157608 • 2 specs; Loki’s Castle hydrothermal vent field; 73.5673° N, 8.1573° E; 2314 m depth; 17 Jul. 2010; collected with ROV; sample GS10-ROV07; fixed in 96% ethanol; ZMBN 157611 • 1 spec.; same data as for preceding; mounted on SEM-stub; ZMBN 157684 • 4 specs; Loki’s Castle hydrothermal vent field; 73.5662° N, 8.1610° E; 2335 m depth; 17 Jul. 2010; collected with ROV; sample GS10-ROV06-b; fixed in 96% ethanol; ZMBN 157609 • 5 specs; Loki’s Castle hydrothermal vent field, eastern mound, Joao; 73.5658° N, 8.1610° E; 2385 m depth; 18 Jul. 2010; collected with ROV; sample GS10-ROV09; fixed in formaldehyde and transferred to 75% ethanol; ZMBN 157622 • 1 spec.; same data as for preceding; fixed in 96% ethanol; DNA-voucher: LC12; ZMBN 157512 • 14 specs; same data as for preceding; fixed in 96% ethanol; ZMBN 157612 • 1 spec.; Loki’s Castle hydrothermal vent field; 73.5668° N, 8.1605° E; 2373 m depth; 19 Jul. 2010; fixed in 96% ethanol; DNA voucher: LC13; ZMBN 157613 • 2 specs; Loki’s Castle hydrothermal vent field; 73.5663° N, 8.1610° E; 2350 m depth; 11 Jul. 2015; collected with ROV; sample GS10-ROV10; fixed in 96% ethanol; ZMBN 157614 • 4 specs; Loki’s Castle hydrothermal vent field, barite field; 73.5664° N, 8.1618° E; 2342 m depth; 10 Jul. 2017; fixed in 96% ethanol; ZMBN 157617 • 3 specs; Loki’s Castle hydrothermal vent field, eastern mound, base of chimney; 73.5664° N, 8.1616° E; 2329 m depth; 11 Jul. 2017; collected with ROV; sample GS15-AGR09; fixed in 96% ethanol; ZMBN 157645 • 6 specs; same data as for preceding; ZMBN 157616 • 5 specs; Loki’s Castle hydrothermal vent field, barite field, chimney; 73.5666° N, 8.1624° E; 2344 m depth; 12 Jul. 2017; collected with ROV; sample GS17-ROV21- R1; fixed in 96% ethanol; ZMBN 157615 • 1 spec.; Loki’s Castle hydrothermal vent field, barite field, worm forest; 73.5663° N, 8.1624° E; 2342 m depth; 18 Jul. 2018; collected with ROV; sample GS18-107-ROV26; fixed in 96% ethanol; ZMBN 157619 • 1 spec.; same data as for preceding; ZMBN 157620 • 4 specs; Loki’s Castle hydrothermal vent field, barite field, worm forest; 73.5662° N, 8.1621° E; 2341 m depth; 22 Jul. 2018; collected by ROV; sample GS18- 107-ROV28; fixed in 96% ethanol; ZMBN 157451 • 2 specs; Loki’s Castle hydrothermal vent field, barite field, worm forest; 73.5665° N, 8.1623° E; 2342 m depth; 26 Jun. 2019; collected with ROV; sample GS19-108-ROV19; fixed in 96% ethanol; ZMBN 147555 • 2 specs; same data as for preceding; 73.5664° N, 8.1623° E; 2345 m depth; 29 Jun. 2019; collected with ROV; sample GS19-108-ROV22; fixed in 96% ethanol; ZMBN 138221 • 2 specs; same data as for preceding; ZMBN 138223 • 2 specs; Loki’s Castle hydrothermal vent field, oasis, worm forest; 73.5671° N, 8.1617° E; 2356 m depth; 1 Jul. 2019; collected with ROV; sample GS19-108-ROV25; fixed in 96% ethanol; ZMBN 138217 • 1 spec.; same data as for preceding; ZMBN 138218 • 15 specs; Loki’s Castle hydrothermal vent field, oasis, worm forest; 73.567° N, 8.1617° E; 2356 m depth; 14 Jul. 2022; collected with ROV; sample GS22-108- ROV575; fixed in 96% ethanol; ZMBN 157500 • 1 spec.; Loki’s Castle hydrothermal vent field, eastern mound, base of chimney; 73.5664° N, 8.16° E; 2313 m depth; 10 Jul. 2017; collected with ROV; sample GS17-ROV18-SS5; fixed in 96% ethanol; ZMBN 157618.
Description
Complete specimens 5–8 mm long and 0.2–0.9 mm wide for 27–35 segments. Colour in ethanol dark brown to black, rarely light tan. Wide and convoluted dark heart body distinctly visible from segment 11–12 to 16–18. Body short, anterior and median chaetigers bead-shaped, transitioning in posterior half or third in distinct flattened region with short and wide segments. Anterior and middle segments twice as high and wide as long, or up to as wide and high as long; posterior segments up to four times wider and three times higher than long. Dorsal groove or ridge absent. Ventral ridge present along posterior part of body (Fig. 8). Large portion of individuals regenerating anterior or posterior parts of body.
Prostomium short, rounded, dorsoventrally flattened; nuchal organs large rounded ciliary fields at posterior dorsolateral margins connected by transversal ventral ciliary bands. Peristomium short, fused with chaetiger 1 in single ovoid bead, with ventral groove separating them; ciliary field present ventrally, continuing as longitudinal band through several anterior segments (Fig. 9B). Branchiae arising from posterior segmental margins, slightly above notopodia, present as early as segment 6 and as far as segment 16.
Parapodia reduced, chaetae emerging directly from body wall. Anterior and midbody neuropodia with 2–5 capillaries; anterior notopodia with 5–7 capillaries; midbody notopodia with up to 11 chaetae; posterior notopodia with 1–3 chaetae. Capillary chaetae long, in mid-body notopodia few capillaries longer than body width, flat, finely serrated along one edge with distinctly round tip. Neuropodia with 3–5 pectinate chaetae from chaetiger 1–3, finely to coarsely serrated along one edge with distinct rounded tip. Neuropodial pectinate chaetae progressively transitioning to spines, 1–2 per neuropodium; 1–3 per notopodium from posterior third of body; straight along most of their length and curving at tip, pointed, with fine serration on concave side becoming coarser posteriorly (Fig. 9A, C-H).
Pygidium with terminal anus, rounded.
Methylene blue staining pattern
Specimens do not retain any colour except for the tip of the prostomium that stains dark blue.
Comparative remarks
The specimens presented here agree well with the original description, with slight differences in chaetal numbers or distribution and in characters related to the heart body. Differences in chaetal numbers can be attributed to intraspecific variability. In the ethanol fixed specimens available for this study, the heart body was always much darker than described in the original description, and usually only the wide, convoluted part was visible. However, the location of this part of the heart body observed in the material matches well the original description.
Raricirrus arcticus is most similar to Raricirrus beryli, the only other species of the genus reported from the area. Differences include morphology, the segment where the heart body starts (segment 2 in R. arcticus or 7 in R. beryli, Buzhinskaja & Smirnov 2017), and the depth range where they occur: 60–300 m for R. beryli (Petersen & George 1991) vs 2000–2500 m for R. arcticus. The morphology of nuchal organs has been proposed as a diagnostic character between both species, R. beryli was described with nuchal organs without cilia surrounded by ciliary patches and R. arcticus was described with nuchal organs inconspicuous among ciliary patches (Buzhinskaja & Smirnov 2017). Nuchal organs in cirratulids have been described as ciliated pits or pits surrounded by cilia and the possibility of eversion of these structures has been proposed as an explanation for the observed variation in this structure (Blake & Magalhães 2017). Personal observations of several species indeed show variation in the shape of nuchal organs due to retraction which could be natural or a consequence of fixation. In particular, specimens of R. beryli have been observed with simple rounded ciliary patches on the prostomium without conspicuous non-ciliated nuchal organs (M. Grosse pers. obs.). Therefore, we propose that this character is an artefact and not diagnostic.
Distribution and habitat
Raricirrus arcticus has been recorded from only two locations: the Laptev Sea (Buzhinskaja & Smirnov 2017) and Loki’s Castle vent field (Eilertsen et al. 2024), from around 2000 to 2500 m deep. At LCVF, it was most common in the Barite Field and the Oasis, but also found on the Eastern Mound at the base of a chimney. Raricirrus arcticus is considered to be a chemosynthetic-based ecosystem specialist (Eilertsen et al. 2024).
description: Published as part of Grosse, Maël, Kongsrud, Jon Anders, Alvestad, Tom, Eilertsen, Mari Heggernes & Budaeva, Nataliya, 2025, A new species and a new record of Cirratulidae (Annelida, Cirratulida) from Loki's Castle vent field, pp. 1-25 in European Journal of Taxonomy 987 on pages 14-18, DOI: 10.5852/ejt.2025.987.2855, http://zenodo.org/record/15264662