Prionospio sp. 6

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 : 49-52

Prionospio sp. 6

Fig. 22; Table 3

Prionospio sp. 6 – Hektoen et al. 2024: figs 1, 4.

Diagnosis

Prostomium narrow, anteriorly rounded, posteriorly extending to middle of chaetiger 1 as a short caruncle. Eyes absent. One pair of apinnate branchiae on chaetiger 3. Notopodial postchaetal lamellae of chaetiger 3 largest, rounded, of chaetigers 2 and 4 triangular. Dorsal crests absent. Neuropodial postchaetal lamellae oblong. Sabre chaetae in neuropodia from chaetiger 10. Hooded hooks in neuropodia from chaetigers 10–11.

Material examined

NORWAY – Vestland • 1 spec.; Høyanger, Torvund ; 61.13583° N, 5.75473° E; depth 1255 m; 3 May 2017; Bergen University Museum leg.; stn KB 2017-05-05 GR; van Veen grab; SEM stub; ZMBN 152561 • 1 spec.; Bømlo, Sveio ; 59.56729° N, 5.21568° E; depth 328 m; 28 Apr. 2017; Bergen University Museum leg.; stn KB-20; van Veen grab; ZMBN 152636 .

Examined material with sequence data

NORWAY – Vestland • 1 spec; Sognefjorden ; 61.05012° N, 5.40056° E; depth 1236 m; 3 May 2017; Bergen University Museum leg.; stn kb 2017-05-02; van Veen grab; ZMBN 152637 .

Description

Three specimens examined, all 0.1 mm wide or smaller. One specimen likely complete, but damaged posteriorly, in three fragments totaling 40 chaetigers. Color in alcohol pale white. Prostomium narrow, anteriorly rounded ( Fig. 22A–B), extending to middle of chaetiger 1 as a short caruncle. Eyes absent. Posterior dorsolateral parts of peristomium fused with notopodial postchaetal lamellae of chaetiger 1 forming ear-shaped structures lateral to prostomium. Palps in one specimen, broken, as long as four chaetigers ( Fig. 22A).

One pair of branchiae on chaetiger 3 in all three specimens, with no scars visible on other chaetigers. Branchiae apinnate, with lateral ciliation, triangular, shorter than notopodial postchaetal lamellae on the same chaetiger ( Fig. 22A). Nototrochs transverse ciliary bands between branchial bases. Dorsolateral longitudinal ciliation absent.

Notopodial prechaetal lamellae inconspicuous. Notopodial postchaetal lamellae of chaetiger 1 rounded, fused with peristomium. Lamellae of chaetiger 2 triangular; lamellae of chaetiger 3 greatly enlarged, rounded, with a small, elongated tip; lamellae triangular on chaetiger 4, rounded on chaetiger 5, lower and oval-shaped on succeeding chaetigers. Dorsal crests absent. Neuropodial prechaetal lamellae inconspicuous. Neuropodial postchaetal lamellae of chaetiger 1 small and oblong; lamellae of chaetigers 2–7 rectangular, broader than high; lamellae lower and rounded on succeeding chaetigers ( Fig. 22A–B). Interneuropodial pouches absent.

Capillary chaetae in single rows in all chaetigers, alimbate and smooth. Sabre chaetae in neuropodia from chaetiger 10. Hooded hooks in notopodia not observed. Hooded hooks in neuropodia from chaetigers 10–11.

Pygidium missing in all specimens.

Remarks

Prionospio sp. 6 is represented only by three small incomplete specimens which could be juveniles with not yet fully developed features. Although molecular data of one of these specimens distinguished it from other Prionospio ( Hektoen et al. 2024: figs 1, 4), we do not formally name it pending examination of additional specimens.

The species does bear resemblance to other small-sized species of Prionospio and Aurospio but can be distinguished morphologically from all such species ( Table 3).

Habitats and distribution

Prionospio sp. 6 was collected from Norwegian fjords in the northern part of the North Sea and southern part of the Norwegian Sea. Worms were found in silty and muddy sediments at depths of 328–1255 m.

Identification key to the species of adult Prionospi o Malmgren, 1867 i n Northern Europe

1. At least some branchiae with pinnules ............................................................................................. 2 – All branchiae apinnate ...................................................................................................................... 6

2. Pinnate branchiae on chaetigers 2, 3 and 5, pinnules on branchiae of chaetiger 3 may only be present basally .................................................................... Prionospio plumosa M. Sars in G.O. Sars, 1872 – Pinnate branchiae otherwise ............................................................................................................. 3

3. Dorsal crests absent ...................................... Prionospio multisetosa Delgado-Blas & Peraza, 2024 – Dorsal crests present ......................................................................................................................... 4

4. High dorsal crest present on chaetiger 7 only ........................... Prionospio fallax Söderström, 1920 – Dorsal crests present on more than one chaetiger ............................................................................ 5

5. Dorsal crests from chaetiger 6, membranous folds between successive notopodia on some chaetigers between chaetigers 4 and 17 ............................................... Prionospio steenstrupi Malmgren, 1867 – Dorsal crests from chaetiger 7, membranous folds between successive notopodia absent ................. ................................................................................................... Prionospio sigvaldadottirae sp. nov.

6. One pair of branchiae on chaetiger 3 ........................................................................ Prionospio sp. 6 – More than one pair of branchiae ....................................................................................................... 7

7. 2–5 pairs of branchiae from chaetiger 2 or 3 (usually three pairs of branchiae from chaetiger 3). Low dorsal crests from chaetiger 6–9 ............................................ Prionospio banyulensis Laubier, 1966 – At least five pairs of branchiae from chaetiger 2. Dorsal crests from chaetiger 10 or later ............. 8

8. Up to six pairs of branchiae. Prostomium extending to end of chaetiger 2. Lower part of neuropodial postchaetal lamellae of chaetiger 2 elongated and pointed downwards ............................................. ................................................................................................ Prionospio cirrifera Wirén, 1883 agg.

– Up to 13 pairs of branchiae. Prostomium extending at the most to the middle of chaetiger 2. Lower part of neuropodial postchaetal lamellae of chaetiger 2 rounded ..................................................... 9

9. Prostomium anteriorly rounded, narrow caruncle extending to middle of chaetiger 2. Median eyes small or large .............................. Prionospio sanmartini Delgado-Blas, Díaz-Díaz & Viéitez, 2019

– Prostomium triangular, anteriorly truncate, thick caruncle extending to end of chaetiger 1. Eyes indistinct in all individuals ..................................................................... Prionospio fiordica sp. nov.