Prionospio plumosa M. Sars

Hektoen, Martin M., Radashevsky, Vasily I. & Bakken, Torkild, 2025, Partial revision of northern European Prionospio Malmgren, 1867 (Annelida: Spionidae), European Journal of Taxonomy 1027, pp. 1-58 : 34-40

Prionospio plumosa M. Sars in G.O. Sars, 1872

Figs 15–17

Prionospio plumosus M. Sars in G.O. Sars, 1872: 410–411.

Prionospio ( Prionospio) tripinnata Maciolek, 1985: 343–345 , fig. 6. Syn. nov.

Prionospio plumosus – Sars 1873: 263–268, figs 13–29. — Bidenkap 1894: 94.

Prionospio steenstrupi – Bidenkap 1894: 93.

Prionospio plumosa – Söderström 1920: 233–234, fig. 141. — Kirkegaard 1996: 86, fig. 39. — Hektoen et al. 2024: figs 1, 4.

Prionospio ( Prionospio) plumosa – Hartmann-Schröder 1996: 326–327.

Prionospio sp. – Gaudron et al. 2010: 5 (genetic data). — Rubin-Blum et al. 2014 (genetic data).

Diagnosis

Prostomium triangular, anteriorly truncate, posteriorly extending to end of chaetiger 1 as a short caruncle. Eyes absent in adults. Four pairs of branchiae on chaetigers 2–5; those of chaetigers 2, 3 and 5 with digitiform pinnules, branchiae of chaetiger 4 apinnate. Branchiae of chaetigers 2 and 5 long, with naked distal tips, on chaetigers 3 and 4 short and stout. Neuropodial postchaetal lamellae of chaetiger 2 not elongated ventrally. Dorsal crests from chaetiger 6 or 7. Sabre chaetae in neuropodia from chaetigers 10– 12, with heavily granulated distal part. Hooded hooks in notopodia from chaetigers 26–43, in neuropodia from chaetigers 12–14.

Type material of Prionospio plumosa

Neotype (designated here)

NORWAY • Filtvedt , Braendtangen, Drøbaksundet; 18 Aug. 1910; Hvitfisken Kristianiafjorden leg.; van Veen grab; NHMO C7075 .

Type material of Prionospio tripinnata

Holotype

LIBYA • 33°57.000′ N, 15°8.202′ E; depth 500–509 m; 2 Sep. 1970; Atlantis II R/V 59 leg.; stn 211; USNM 67678 .

Other material examined

SWEDEN – Bohuslän • 5 specs; Väderön ; depth 109 m; 29 Jun. 1869; stn VädOls6; SMNH 120288 .

NORWAY – Rogaland • 1 spec.; Sauda ; depth 38 m; 6 May 1981; stn7; NTNU-VM 25670 • 10 specs; Bokn, Lådeskjera ; 59°11.893′ N, 5°28.880′ E; depth 102 m; 4 Apr. 2021; Åkerblå AS leg.; stn LÅD-1; van Veen grab; NTNU-VM 84075 . – Vestland • 2 specs.; Ullensvang, Hessvik ; 0°07.754′ N, 6°09.062′ E; depth 66 m; 1 Jul. 2010; SAM leg.; stn HES 1-1; van Veen grab; SMNH 129904 • 1 spec.; Bergen, Lyreneset ; 60°23.692′ N, 5°16.214′ E; depth 34 m; 6 Jun. 1999; SAM leg.; stn Lyr 2-1, van Veen grab; SMNH 129905 • 20 specs; Gulen, Hardbakkeneset ; 61°01.003′ N, 4°57.039′ E; depth 80 m; 19 Sep. 2019; Åkerblå AS leg.; stn HAR-1; van Veen grab; NTNU-VM 84082 • 15 specs; Fjaler, Hegnes ; 61°21.470′ N, 5°17.110′ E; depth 244 m; 4 Dec. 2019; Åkerblå AS leg.; stn HEG-1; van Veen grab; NTNU-VM 84079 • 2 specs; Flora, Vågsøya ; 61°29.177′ N, 5°01.489′ E; depth 71 m; 31 Oct. 2019; Åkerblå AS leg.; stn VÅG-1; van Veen grab; NTNU-VM 84080 • 30 specs; Bremanger Gulestø ; 61°45.515′ N, 5°04.437′ E; depth 145 m; 8 Oct. 2019; Åkerblå AS leg.; stn GUL-1; van Veen grab; NTNU-VM 84078 • 2 specs; same data as for preceding; SEM stub; NTNU-VM 85856 • 1 spec.; same data as for preceding; SEM stub; NTNU-VM 85855 • 2 specs; Selje, Beitveit ; 62°08.325′ N, 5°19.764′ E; depth 117 m; 10 Oct. 2019; Åkerblå AS leg.; stn BEI-1; van Veen grab; NTNU-VM 84091 • 20 specs; Alver, Jibbersholman ; 60°45.052′ N, 4°53.330′ E; depth 80 m; 18 Dec. 2019; Åkerblå AS leg; stn JIB-4; van Veen grab; NTNU-VM 84076 • 5 specs; Gulen, Lyngholmen ; 61°00.924′ N, 5°00.550′ E; depth 112 m; 20 Apr. 2021; Åkerblå AS leg.; stn LYN-1; van Veen grab; NTNU-VM 84084 • 10 specs; Fjaler, Kyravika ; 61°19.115′ N, 5°09.559′ E; depth 400 m; 14 Dec. 2021; Åkerblå AS leg.; stn KYR-1; van Veen grab; NTNU-VM 84081 • 20 specs; Bremanger, Juvika B; 61°53.805′ N, 5°38.062′ E; depth 186 m; 9 Dec. 2021; Åkerblå AS leg.; stn JUV-1; van Veen grab; NTNU-VM 84088 • 2 specs; Bergen, Brettesnes ; depth 36–55 m; M. Sars leg.; van Veen grab; NHMO C7022 . – Møre og Romsdal • 25 specs; Stranda, Opshaugvik ; 62°17.350′ N, 6°59.630′ E; depth 376 m; 31 Mar. 2020; Åkerblå AS leg.; stn OPS-3; van Veen grab; NTNU-VM 84093 • 17 specs; Fraena, Storvika ; 62°48.113′ N, 6°58.539′ E; depth 182 m; 24 Sep. 2019; Åkerblå AS leg.; stn STO-1; van Veen grab; NTNU-VM 84074 • 1 spec.; Gjemnes, Høybuvika ; 62°57.443′ N, 8°03.334′ E; depth 285 m; 14 Dec. 2021; Åkerblå AS leg.; stn HØY-3; van Veen grab; NTNU-VM 84077 • 20 specs; Høybuvika ; 62°57.545′ N, 8°03.082′ E; depth 281 m; 14 Dec. 2021; Åkerblå AS leg.; stn HØY-1; van Veen grab; NTNU-VM 84086 • 15+ specs; Ørsta, Sagelva ; 62°20.277′ N, 6°23.084′ E; depth 186 m; 7 Oct. 2020; Åkerblå AS leg.; stn SAG-1; van Veen grab; NTNU-VM 84085 • 1 spec.; same data as for preceding; SEM stub; NTNU-VM 85857 • 1 spec.; same data as for preceding; SEM stub; NTNU-VM 85858 • 10 specs; Kristiansund, Endreset ; 63°01.893′ N, 7°42.726′ E; depth 203 m; 10 Sep. 2019; Åkerblå AS leg.; stn END-4; van Veen grab; NTNU-VM 84087 . – Trøndelag • 5+ specs; Heim, Vullum ; 63°02.888′ N, 8°12.819′ E; depth 282 m; 3 Aug. 2021; Åkerblå AS leg.; stn VUL-1; van Veen grab; NTNU-VM 84090 • 13 specs; Fiborgtangen ; 63.7165° N, 11.1457°; depth 30 m; 1983; stn 13; van Veen grab; NTNU-VM 25391 • 3 specs; same data as for preceding; NTNU-VM 25389 • 5 specs; same data as for preceding; NTNU-VM 25390 • 1 spec.; Ørland, Storforsna, Vågen ; 63.6541° N, 9.4069° E; depth 80–120 m; 1951; E. Sivertsen leg.; NTNU-VM 25797 . – Troms • 5 specs; Tromsø, Tromsø ; depth 273 m; 30 Jun. 2010; van Veen grab; SMNH 129903 .

Examined material with sequence data

NORWAY – Vestland • 1 spec.; Fjaler , Hegnes; 61°21.470′ N, 5°17.110′ E; depth 244 m; 4 Dec. 2019; Åkerblå AS leg.; stn HEG-1; van Veen grab; NTNU-VM 84089 • 1 spec.; Selje , Beitveit; 62°08.325′ N, 5°19.764′ E; depth 117 m; 10 Oct. 2019; Åkerblå AS leg.; stn BEI-1; van Veen grab; NTNU-VM 84092 • 1 spec.; Alver , Jibbersholman; 60°45.052′ N, 4°53.330′ E; depth 80 m; 18 Dec. 2019; Åkerblå AS leg.; stn JIB-4; van Veen grab; NTNU-VM 84094 • 1 spec.; Bergen , Flesland; 60°17.052′ N, 5°12.087′ E; depth 72 m; 2 Sep. 2014; Bergen University Museum leg.; stn HB 2014.09.02 -1; van Veen grab; ZMBN 152635 . – Nordland • 1 spec.; Alstahaug , Skorpa; 66°01.900′ N, 12°28.864′ E; depth 107 m; 22 Nov. 2019; Åkerblå AS leg.; stn NSK-1; van Veen grab; NTNU-VM 84083 .

Description (adults)

Neotype ( NHMO C7075) anterior fragment, 18 mm long, 1.7 mm wide, with 30 chaetigers, too damaged for close morphological examination after chaetiger 20. Color in alcohol pale brown to white. Prostomium triangular, anteriorly truncate, posteriorly extending to end of chaetiger 1 as a short, narrow caruncle. Nuchal organs U-shaped ciliary bands lateral to caruncle ( Fig. 15A). Neotype without eyes, some small specimens with faint lateral eyespots ( NTNU-VM 84077, 84085; Fig. 15B–C). Posterior dorsolateral parts of peristomium fused with notopodial postchaetal lamellae of chaetiger 1, forming ear-shaped structures lateral to prostomium. Palps missing in all specimens.

Branchiae on chaetigers 2–5; those of chaetigers 2, 3 and 5 with digitiform pinnules on anterior sides; branchiae of chaetiger 4 apinnate. Branchiae of chaetigers 2 and 5 long, rounded in cross section, those of chaetigers 3 and 4 shorter, triangular in cross section ( Fig. 15A) with dense lateral ciliation, distally flattened, foliaceous ( Figs 15C–D, 16C–D). Branchiae of chaetiger 2 with apinnate basal part, densely pinnate on anterior side three-fourths up the branchiae, ending in apinnate tip ( Fig. 16B). Branchiae of chaetiger 3 sparsely pinnate on anterior side halfway to two-thirds up branchiae ( Fig. 16C). Branchiae of chaetiger 4 apinnate, with raised edge running up the branchia ( Figs 15A, 16D); branchiae of chaetiger 5 densely pinnate on anterior side along almost entire length, with short slender apinnate tip ( Fig. 16E). Nototrochs transverse ciliary bands between branchial bases on chaetigers 2–5. Dorsolateral longitudinal ciliation present between chaetigers 4–6.

Notopodial prechaetal lamellae small, rounded on anterior chaetigers, reduced in posterior chaetigers. Notopodial postchaetal lamellae of chaetiger 1 triangular ( Figs 16A, 17A), fused with peristomium, on chaetigers 2–5 large and subtriangular, largest on chaetiger 3 ( Figs 16B–E, 17A). Lamellae rapidly diminishing in size, lower and rounded in postbranchial chaetigers, assuming low oval shape from chaetigers 8–9 ( Fig. 16F–H). Notopodial postchaetal lamellae joined across dorsum forming transverse crests from chaetiger 6 to chaetigers 10–15, crest highest on chaetiger 7 ( Figs 15A, C–D, 16F–H). Crest not visible at all on chaetiger 6 in some smaller specimens. Neuropodial prechaetal lamellae inconspicuous. Neuropodial postchaetal lamellae of chaetiger 1 broadly rounded, about one third to half the size of lamellae on subsequent chaetigers ( Figs 16A, 17A); lamellae of chaetiger 2 subrectangular, higher than broad with rounded edges ( Figs 16B, 17A); lamellae of chaetiger 3 oval, broad ( Figs 16C, 17A); lamellae of chaetiger 4 quadrangular with rounded edges ( Figs 16D, 17A); lamellae of subsequent chaetigers rounded, low and oval by chaetiger 12 ( Fig. 16E–H), reduced on succeeding chaetigers. Interneuropodial pouches absent.

Notopodial capillaries on anterior chaetigers arranged in numerous rows (7+), unilimbate and slightly granulated. Notopodial capillaries on middle chaetigers in two rows, unilimbate and slightly granulated. Neuropodial capillaries arranged in two rows in anterior chaetigers, unilimbate, granulated, anterior row shorter than posterior row. Posterior chaetae not observed in neotype, but notopodial capillaries in posterior chaetigers long, thin, alimbate and granulated in other specimens ( NTNU-VM 85856). Sabre chaetae in neuropodia from chaetigers 10–12 (chaetiger 10 in neotype) with strong granulation on median and distal parts of shaft, up to 10 per fascicle in neotype, up to three in smaller specimens ( Fig. 17B). Hooded hooks in notopodia not present in neotype, from chaetigers 26–47 in other specimens ( NTNU-VM 84090), up to six per ramus. Hooded hooks in neuropodia from chaetiger 12–14 ( 14 in neotype), up to eight per ramus. Both notopodial and neuropodial hooks with 3–4 pairs of upper teeth arranged in two vertical tows above main fang, with only outer hood, secondary inner hood absent ( Fig. 17C).

Pygidium with one long middorsal cirrus and one pair of short ventral cirri ( NTNU-VM 84084, 84086, 84093), missing in neotype.

Remarks

A brief original description of Prionospio plumosus by Michael Sars was published after his death ( 22 October 1869) by his son, a Norwegian marine and freshwater biologist and professional illustrator Georg Ossian Sars (1872). The original description was based on an unknown number of specimens from the Drøbak sound, southern Norway. Later, Sars (1873) provided a detailed description and illustrations of this species. The type material was likely originally stored in the Natural History Museum, Oslo, but was not located by us or the curator of the NHMO (Ann-Helén Rønning pers. comm.). Sigvaldadóttir (1998) listed the type material of P. plumosa as deposited in the polychaete collection of the Smithsonian Institution, Washington D.C. (USNM 32698). However, neither the authors or curators were able to locate this material in the museum and the noted catalogue number is currently assigned to the holotype of Prionospio ornata Berkeley & Berkeley, 1961 from Peru (http://n 2t.net/ark:/65665/308a8bc18-4af6-4154-8d3b-e822fb633267). Therefore, we consider the types of P. plumosa to be lost. To ensure nomenclatural stability, we designate here a neotype (NHMO C7075). The specimen was collected in 1910 between Filtvet and Brenntangen in the Oslofjord, which is a narrow stretch of approximately 1.5 km long and depth up to 200 m. No further information is given on the label. The noted location is about 10 km south of the original type locality at Drøbak ( Sars 1872; Oug et al. 2014). Prionospio plumosa is rare, if still occurring, in the Oslofjord. The species has not been reported in the region in over a century, despite targeted sampling of Sars’ type localities in the past decade ( Oug et al. 2015).

Prionospio tripinnata Maciolek, 1985 was described based on a single specimen from a depth of 500 m in the Mediterranean Sea ( Maciolek 1985). The species was differentiated from P. plumosa by the branchiae of chaetigers 3 and 4 being shorter and stouter than those on chaetigers 2 and 5, and the branchiae of chaetiger 3 having only a basal patch of pinnules instead of having pinnules along ⅔ of the length. Sars (1873) noted regarding the length of the branchiae that “3 die og 2 det Par omtrent ligestore og kun halvt saa lange som første og sidste Par” (the 3 rd and 2 nd pairs are approximately equal in size, and ½ as long as the first and last pairs). This is also apparent in the provided illustrations ( Sars 1873: pl. xvii figs 13–14). Regarding the differences in the distribution of the pinnules on the branchiae of chaetiger 3, it can be considered due to worms studied being of different sizes. Sars (1873) described a specimen that was 30 mm long and 1.5 mm wide, while the only specimen of P. tripinnata was 12 mm long and 0.75 mm wide. Upon examination of the holotype of P. tripinnata , we found it similar to smaller specimens of P. plumosa from Norway and Sweden. Prionospio tripinnata is accordingly considered a junior synonym of P. plumosa . The molecular analysis by Hektoen et. al. (2024) also indicated that P. plumosa is present in deep waters in the Eastern Mediterranean.

Prionospio plumosa can be distinguished from all other Prionospio by the presence of digitiform pinnules on the branchiae of chaetigers 2, 3 and 5. To our knowledge, it is the only species, together with Prionospio kirrae Wilson, 1990 , with pinnules covering the anterior side of the branchiae (the branchiae of chaetiger 5 in P. kirrae ) rather than the posterior and/or lateral sides. Dorsal crests in the examined specimens of P. plumosa were present from either chaetiger 6 or 7. The worms sequenced by Hektoen et al. (2024) included specimens with dorsal crests both from chaetiger 6 and 7, indicating that the absence of crest on chaetiger 6 is either intraspecific variation or a preservation artifact.

Prionospio plumosa has been noted as rare in taxonomic literature ( Sars 1872; Bidenkap 1894; Söderström 1920; Kirkegaard 1996), with sparse records in the 20 th century. However, in the last decade, P. plumosa has been frequently reported in ecological surveys near aquaculture sites in Norway. The species was originally described from dead algal fragments ( Sars 1873), indicating that the type locality was an area where organic matter accumulated, perhaps mirroring conditions close to modern day finfish farms. Through the examination of unidentified material in various museum collections, additional specimens collected in the 20 th century were discovered, amending the spotty records, including the 1910 neotype (NHMO C7075) and specimens from the Trondheimsfjord ( Norway) collected in 1951 (NTNU-VM 25797) and the 1980s (NTNU-VM 25389–25391).

Habitats and distribution

Prionospio plumosa is common along the Norwegian coast, most often in muddy and silty sediments affected by high organic load at depths of 34– 500 m. It has also been recorded from the Mediterranean Sea at depths of 500–1000 m.