taxonID	type	description	language	source
09528795FFD2FFBA6220FDD6D94EFC37.taxon	type_taxon	Type species Cirratulus viridis Langerhans, 1880. Original designation by Chamberlin (1919).	en	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. European Journal of Taxonomy 987: 1-25, DOI: 10.5852/ejt.2025.987.2855, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2855/12979
09528795FFD2FFBA6220FDD6D94EFC37.taxon	diagnosis	Diagnosis (after Blake 2021) Prostomium elongate, conical to pointed; peristomium elongated to short, dorsal tentacles usually beginning anterior to chaetiger 1. Middle body segments not beaded; parapodia often with noto- and neuropodia widely separated laterally. Chaetae including capillaries and bidentate, crotchet-like hooks, not arranged into modified cinctures. In some species, unidentate hooks may occur in some regions of body in addition to bidentate hooks. Pygidium either simple conical lobe or with one or two anal cirri.	en	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. European Journal of Taxonomy 987: 1-25, DOI: 10.5852/ejt.2025.987.2855, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2855/12979
09528795FFD2FFB16252FBB8D881FC47.taxon	description	urn: lsid: zoobank. org: act: FF 0 D 1 D 4 D- 39 A 7 - 48 ED-A 5 DD-E 457 E 1 A 47 D 20 Figs 3 – 7	en	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. European Journal of Taxonomy 987: 1-25, DOI: 10.5852/ejt.2025.987.2855, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2855/12979
09528795FFD2FFB16252FBB8D881FC47.taxon	diagnosis	Diagnosis Body long and slender, not threadlike, posteriorly flattened; three peristomial rings, first segment chaetigerous; 3 – 6 bidentate spines per neuropodium from chaetiger 4, 3 – 4 per notopodium from chaetiger 16.	en	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. European Journal of Taxonomy 987: 1-25, DOI: 10.5852/ejt.2025.987.2855, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2855/12979
09528795FFD2FFB16252FBB8D881FC47.taxon	etymology	Etymology In Norse mythology, Jörmungandr is a sea serpent or worm and a child of Loki. As a marine worm discovered in the Loki’s Castle vent field, Caulleriella jormungandri sp. nov. is named after this mythological creature.	en	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. European Journal of Taxonomy 987: 1-25, DOI: 10.5852/ejt.2025.987.2855, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2855/12979
09528795FFD2FFB16252FBB8D881FC47.taxon	materials_examined	Material examined Holotype ARCTIC MID-OCEAN RIDGE • Loki’s Castle hydrothermal vent field; 73.56633 ° N, 8.15946 ° E; 2350 m depth; 11 Jul. 2015; collected by ROV; sample GS 15 - AGR 09; fixed in 96 % ethanol; DNAvoucher: CaH 03; ZMBN 157421. Paratypes 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 by ROV; sample BIODEEP 08 - LC-ROV 11; fixed in 96 % ethanol; ZMBN 157515 • 1 spec.; Loki’s Castle hydrothermal vent field, Barite Field; 74.5661 ° N, 8.1585 ° E; 2357 m depth; 7 Aug. 2009; collected by ROV; sample H 2 DEEP 09 - ROV 08; fixed in 96 % ethanol; ZMBN 157516 • 1 spec.; same data as for preceding; DNA-voucher: LC 01; ZMBN 157517 • 1 spec.; same data as for preceding; DNA-voucher: LC 04; ZMBN 157518 • 1 spec.; same data as for preceding; ZMBN 157520 • 1 spec.; same data as for preceding; DNA-voucher: LC 02; ZMBN 157513 • 1 spec.; same data as for preceding; DNA-voucher: LC 03; ZMBN 157514 • 1 spec.; same data as for preceding; DNA-voucher: LC 05; ZMBN 157519 • 3 specs; same data as for preceding; mounted on SEM-stubs; ZMBN 157681 to 157683 • 1 spec.; Loki’s Castle hydrothermal vent field; 73.5662 ° N, 8.1610 ° E; 2335 m depth; 17 Jul. 2010; collected by ROV; sample GS 10 - ROV 06 - b; fixed in 96 % ethanol; ZMBN 157521 • 1 spec.; same data as for preceding; 73.5668 ° N, 8.1605 ° E; 2373 m depth; 19 Jul. 2010; collected by ROV; sample GS 10 - ROV 10; fixed in 96 % ethanol; ZMBN 157522 • 109 specs; same data as for preceding; 73.5663 ° N, 8.1610 ° E; 2350 m depth; 11 Jul. 2015; collected by ROV; sample GS 15 - AGR 09; fixed in 96 % ethanol; ZMBN 154069 • 3 specs; same data as for preceding; DNA vouchers: K 49, K 50, K 51; no repository (specimens used for DNA) • 1 spec.; same data as for preceding; DNAvoucher: CaH 01; ZMBN 157419 • 1 spec.; same data as for preceding; DNA-voucher: CaH 02; ZMBN 157420 • 1 spec.; same data as for preceding; DNA-voucher: CaH 04; ZMBN 157422 • 1 spec.; same data as for preceding; DNA-voucher: CaH 05; ZMBN 157423 • 1 spec.; Loki’s Castle hydrothermal vent field, barite field; 73.5664 ° N, 8.1618 ° E; 2342 m depth; 10 Jul. 2017; collected by ROV; sample GS 17 - ROV 18 - SS 4; fixed in 96 % ethanol; ZMBN 157524 • 8 specs; Loki’s Castle hydrothermal vent field, barite field, chimney; 73.5666 ° N, 8.1624 ° E; 2344 m depth; 12 Jul. 2017; collected by ROV; sample GS 17 - ROV 21 - R 1; fixed in 96 % ethanol; ZMBN 157523 • 2 specs; Loki’s Castle hydrothermal vent field, barite field, worm forest; 73.5663 ° N, 8.1624 ° E; 2342 m depth; 18 Jul. 2018; collected by ROV; sample GS 18 - 107 - ROV 26; fixed in 96 % ethanol; ZMBN 157597 • 1 spec.; same data as for preceding; ZMBN 157598 • 2 specs; same locality as for preceding; 73.5662 ° N, 8.1621 ° E; 2341 m depth; 22 Jul. 2018; collected by ROV; GS 18 - 107 - ROV 28; fixed in 96 % ethanol; ZMBN 157599 • 1 spec.; Loki’s Castle hydrothermal vent field, oasis, worm forest; 73.5671 ° N, 8.1617 ° E; 2356 m depth; 1 Jul. 2019; collected by ROV; GS 19 - 108 - ROV 25; fixed in 96 % ethanol; ZMBN 138216 • 7 specs; same data as for preceding; fixed in 96 % ethanol; ZMBN 138212. Other material ARCTIC MID-OCEAN RIDGE • 37 specs; 68.70600 ° N, 11.61100 ° W; 1811 m depth; 16 Mar. 1984; collected by dredge; sample HM 84.03.16 - 2; fixed in formaldehyde and transferred to 75 % ethanol; ZMBN 144543 • 6 specs; 69.60600 ° N, 9.91000 ° W; 2212 m depth; 26 Jul. 1986; collected by dredge; sample HM 86.07.26 - 1; fixed in formaldehyde and transferred to 75 % ethanol; ZMBN 157644 • 1 spec.; 69.10616 ° N, 9.9120 ° W; 2174 – 2204 m depth; 17 Sep. 2011; sample M 85 - 3 - 1155; fixed in 96 % ethanol; DNA-voucher: MG 1000; SMF 32807 • 1 spec.; same data as for preceding; DNA-voucher: MG 1001; no repository (specimen used for SEM) • 1 spec.; 69.103 ° N, 9.9225 ° W; 2169 – 2172 m depth; 17 Sep. 2011; collected with Agassiz trawl; sample M 85 - 3 - 1160; fixed in 96 % ethanol; DNA-voucher: MG 763 no repository (specimen used for SEM) • 1 spec.; 71.1110 ° N, 7.92933 ° W; 2160 – 2203 m depth; 17 Sep. 2011; fixed in 96 % ethanol; collected with epibenthic sledge; sample M 85 - 3 - 1159; DNA-voucher: MG 1041; SMF 32878 • 1 spec.; same data as for preceding; DNA-voucher: MG 1042 no repository (specimen used for SEM) • 1 spec.; same data as for preceding; DNA-voucher: MG 1043 no repository (specimen used for SEM) • 1 spec.; same data as for preceding; DNA-voucher: MG 1044; SMF 32879 • 1 spec.; same data as for preceding; DNA-voucher: MG 1045; SMF 32880.	en	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. European Journal of Taxonomy 987: 1-25, DOI: 10.5852/ejt.2025.987.2855, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2855/12979
09528795FFD2FFB16252FBB8D881FC47.taxon	description	Description Holotype complete, 12 mm long, 0.7 mm wide, 72 segments. Other complete specimens ranging 3 – 12 mm in length and 0.2 – 0.7 mm in width for 47 – 77 segments. Colour in ethanol light tan to brown, rarely dark grey (Figs 3 – 4). Body long and slender, without any distinct enlargement, cylindrical in cross section in anterior and middle body, dorsoventrally flattened in posterior region (Figs 3 – 4). Anterior 8 – 13 segments 3 – 4 times wider and higher than long, round in cross section, lengthening to 2 – 3 times wider and higher than long in midbody. Posterior 20 segments 4 – 5 times wider and 2 times higher than long, oval to rectangular in cross section. Dorsal groove or ridge absent. Thin ventral groove accompanied by dark line sometimes present, depending on fixation. Prostomium half to two thirds as long as peristomium, conical, rounded on anterior margin, without rings; eyespots absent (Figs 5 A – C, F, 6 B – C); nuchal organs simple round slits at posterior lateral margins (Fig. 5 C – E). Peristomium as long as 3 – 4 anterior segments, as high and wide as long, with three distinct rings of similar length, anterior ring overlapping prostomium dorsally, middle ring overlapping posterior ring dorsally between tentacles, posterior ring partially fused to chaetiger 1. Dorsal tentacles arising from third peristomial ring, well separated from one another and anterior to first pair of branchiae (Figs 5 A – C, F, 6 B – C). First pair of branchiae arising between posterior margin of peristomium and first segment postero-lateral to tentacles. Second pair of branchiae arising from chaetiger 1, dorsal and slightly posterior to parapodia (Fig. 5 A – B, F). Subsequent branchiae similarly placed, present only in anterior part of body. Parapodia biramous, neuropodia and notopodia well separated, notopodia forming low shoulders in anterior chaetigers, neuropodia lateral anteriorly and nearly reaching ventral position in posterior chaetigers. Capillary chaetae 8 – 10 per neuropodium and notopodium from chaetiger 1, decreasing in number posteriorly; finely fibrillated along one edge (Fig. 7 A – B). On neuropodia and notopodia without spines, capillary chaetae are arranged in two rows, posterior capillaries twice as long as anterior ones (Fig. 7 A). Bidentate spines from chaetiger 4, 3 – 6 per neuropodium; from chaetiger 16, 3 – 4 per notopodium; long, relatively thick, slightly curved with basal shoulder, main fang thick, pointed, at 45 ° angle from shaft, apical tooth short, pointed, in prolongation of alate flange on convex side of shaft (Fig. 7 C – G). Companion capillaries arise between most spines. Pygidium with terminal anus and rounded ventral lobe (Fig. 6 A). Methylene blue staining pattern The entire body retains a light blue colour with dark blue circles around neuropodia and notopodia anteriorly. Some dark intersegmental ventral bands are sometimes visible on the first few segments.	en	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. European Journal of Taxonomy 987: 1-25, DOI: 10.5852/ejt.2025.987.2855, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2855/12979
09528795FFD2FFB16252FBB8D881FC47.taxon	discussion	Comparative remarks At present, nine species of Caulleriella have been reported from depths over 500 m (Blake 2021), including the new species described in the present paper. One species is known from the Pacific Ocean, four from the Southern Ocean and four from the Atlantic Ocean. Caulleriella jormungandri sp. nov. is most similar to C. eltaninae Blake, 2018 and C. kacyae Blake, 2018 from the Southern Ocean in having three peristomial rings. Caulleriella jormungandri differs from C. eltaninae in that the first segment is the first chaetiger (achaetous in C. eltaninae), in the presence of notopodial spines and in the lack of pygidial cirri. Caulleriella jormungandri mainly differs from C. kacyae by the lack of pygidial cirri and the number and distribution of spines in neuropodia (up to 6 from segment 4 in the former vs up to 6 from segment 18 in the latter) and notopodia (up to 4 from segment 16 in the former vs up to 2 from segment 105 in the latter). Caulleriella jormungandri is easily distinguished from other deep-sea North Atlantic species (Caulleriella filliformia Blake, 2021, Caulleriella pintada Blake, 2021 and Caulleriella rodmani Blake, 2021) by the body shape and the peristomium, as all these other species have threadlike bodies and a single peristomial ring.	en	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. European Journal of Taxonomy 987: 1-25, DOI: 10.5852/ejt.2025.987.2855, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2855/12979
09528795FFD2FFB16252FBB8D881FC47.taxon	distribution	Distribution and habitat Caulleriella jormungandri sp. nov. is a common species at Loki’s Castle vent site in areas with lowtemperature diffuse venting, where it is found in association with dense aggregations of other polychaetes (worm forest), in particular Sclerolinum contortum and Nicomache lokii. Additional specimens were collected from five localities close to Jan Mayen in depths between 1800 and 2200 m (Fig. 1). No indication of hydrothermal activity was recorded from the localities near Jan Mayen, suggesting that Caulleriella jormungandri is not strictly associated with hydrothermal environments.	en	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. European Journal of Taxonomy 987: 1-25, DOI: 10.5852/ejt.2025.987.2855, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2855/12979
09528795FFD9FFB1624DFC17DD98F9F9.taxon	type_taxon	Type species Raricirrus maculatus Hartman, 1961. Original designation.	en	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. European Journal of Taxonomy 987: 1-25, DOI: 10.5852/ejt.2025.987.2855, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2855/12979
09528795FFD9FFB1624DFC17DD98F9F9.taxon	diagnosis	Diagnosis (after Magalhães et al. 2017) Prostomium rounded, eyes absent, nuchal organs shallow ciliary pits, postero-lateral, rounded or elongate. Peristomium not obviously delimited from prostomium and chaetiger 1 dorsally; ventral cilia may be present on peristomium and first few segments; first segment complete chaetiger. Tentacles absent. Branchiae present on several segments, filiform or club-like distally. Notochaetae short and long serrate capillaries anteriorly and modified chaetae posteriorly as acicular spines, coarsely serrate forms and short pectinate falcigers. Neurochaetae short serrate capillaries and / or modified chaetae such as acicular spines, falcate and finely pectinate, and coarsely serrate chaetae. Simple enlarged spines may be present in one or two posterior end segments. Heart body enlarged dorsal vessel present in variable number of anterior and middle segments. Pygidium simple lobe, anal aperture usually dorsal; posterior region distinct with few segments wider than preceding ones. Asexual reproduction via architomy. Sexual reproduction may occur; epitoke individuals, hermaphroditism, seminal vesicle and reproductive stylet may be present.	en	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. European Journal of Taxonomy 987: 1-25, DOI: 10.5852/ejt.2025.987.2855, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2855/12979
09528795FFD9FFAD61E9F9FADD6FF93C.taxon	description	Figs 8 – 9	en	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. European Journal of Taxonomy 987: 1-25, DOI: 10.5852/ejt.2025.987.2855, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2855/12979
09528795FFD9FFAD61E9F9FADD6FF93C.taxon	diagnosis	Diagnosis Heart body from chaetiger 2; branchiae cylindrical; distinct ciliary field near mouth; long serrate chaetae with straight tips in midbody neuropodia.	en	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. European Journal of Taxonomy 987: 1-25, DOI: 10.5852/ejt.2025.987.2855, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2855/12979
09528795FFD9FFAD61E9F9FADD6FF93C.taxon	materials_examined	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 BIODEEP 08 - LC-ROV 11; fixed in 96 % ethanol; DNA voucher: LC 06; 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 BIODEEP 08 - LC-ROV 12; 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 H 2 DEEP 09 - ROV 08; fixed in 96 % ethanol; ZMBN 157686 • 72 specs; same data as for preceding; ZMBN 157602 • 1 spec.; same data as for preceding; DNA-voucher: LC 08; ZMBN 157621 • 1 spec.; same data as for preceding; DNA-voucher: LC 09; 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 GS 10 - ROV 04; fixed in 96 % ethanol; DNA-voucher: LC 07; ZMBN 157509 • 1 spec.; same data as for preceding; DNA-voucher: LC 10; ZMBN 157510 • 1 spec.; same data as for preceding; DNA-voucher: LC 11; 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 GS 10 - ROV 07; 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 GS 10 - ROV 06 - 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 GS 10 - ROV 09; fixed in formaldehyde and transferred to 75 % ethanol; ZMBN 157622 • 1 spec.; same data as for preceding; fixed in 96 % ethanol; DNA-voucher: LC 12; 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: LC 13; 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 GS 10 - ROV 10; 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 GS 15 - AGR 09; 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 GS 17 - ROV 21 - R 1; 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 GS 18 - 107 - ROV 26; 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 GS 18 - 107 - ROV 28; 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 GS 19 - 108 - ROV 19; 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 GS 19 - 108 - ROV 22; 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 GS 19 - 108 - ROV 25; 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 GS 22 - 108 - ROV 575; 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 GS 17 - ROV 18 - SS 5; fixed in 96 % ethanol; ZMBN 157618.	en	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. European Journal of Taxonomy 987: 1-25, DOI: 10.5852/ejt.2025.987.2855, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2855/12979
09528795FFD9FFAD61E9F9FADD6FF93C.taxon	description	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. 9 B). 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. 9 A, 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.	en	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. European Journal of Taxonomy 987: 1-25, DOI: 10.5852/ejt.2025.987.2855, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2855/12979
09528795FFD9FFAD61E9F9FADD6FF93C.taxon	discussion	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.	en	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. European Journal of Taxonomy 987: 1-25, DOI: 10.5852/ejt.2025.987.2855, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2855/12979
09528795FFD9FFAD61E9F9FADD6FF93C.taxon	distribution	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).	en	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. European Journal of Taxonomy 987: 1-25, DOI: 10.5852/ejt.2025.987.2855, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2855/12979
