Genus Prionospio Malmgren, 1867 Prionospio Malmgren, 1867: 201. Prionospio – Blake & Kudenov 1978: 211–212. — Maciolek 1985: 325–283. — Blake et al. 2020: 61–62. Type species Prionospio steenstrupi Malmgren, 1867, by monotypy. Diagnosis Prostomium anteriorly rounded to truncate, with frontal margin entire to weakly incised, rarely with fronto-lateral horns; subtriangular, rectangular or oval in shape, extending posteriorly at least to end of chaetiger 1 as a low caruncle. Nuchal organs U-shaped lateral to caruncle. Red, rarely black eyes present or absent. Occipital antenna absent. Peristomium at least partially fused with notopodial postchaetal lamellae of chaetiger 1, forming low wings to prominent ear-shaped structures on lateral sides of prostomium. Notopodial lamellae of chaetiger 1 small, usually fused with dorsal posterior parts of peristomium; neuropodia lamellae small. Noto- and neuropodial postchaetal lamellae largest on branchiate chaetigers, reduced thereafter. Notopodial lamellae on postbranchiate chaetigers often interconnected by dorsal transverse low ridges to high crests. Interparapodial pouches or membranous folds present or absent. Branchiae usually from chaetiger 2, rarely from chaetiger 3 or absent, limited to anterior part of body, cylindrical or flattened with surfaces perpendicular to body axis, free from notopodial lamellae, smooth, apinnate or with digitiform pinnules. Hooks bi-, tri-, quadri- or multidentate, with inner and/ or rarely only outer hoods, present in noto- and neuropodia; shaft slightly curved, without constriction. Sabre chaetae usually present in neuropodia, rarely absent. Pygidium with one long middorsal cirrus and two shorter ventral cirri; rarely ventral cirri reduced. Remarks This diagnosis mainly follows that of Blake et al. (2020), with addition of characters described by Radashevsky (2012) and as required by accommodation of Prionospio cerastae Radashevsky, 2015 which has fronto-lateral horns on the prostomium.

Published as part of Hektoen, Martin M., Radashevsky, Vasily I. & Bakken, Torkild, 2025, Partial revision of northern European Prionospio Malmgren, 1867 (Annelida: Spionidae), pp. 1-58 in European Journal of Taxonomy 1027 on pages 4-5, DOI: 10.5852/ejt.2025.1027.3127, http://zenodo.org/record/17866576