Eunoe oerstedi Malmgren 1866

Eunoe oerstedi Malmgren, 1866

(Fig. 3 A–H)

Eunoe oerstedi Malmgren, 1866: 61, pl. 8 figs. 3A–D; Pettibone (1954): 219, fig. 26d; Uschakov (1982): 177, pl. 67 figs. 9–10.

Harmothoe (Eunoe) oerstedi: Pettibone (1963): 44, fig. 9d. (for further synonymy see Pettibone 1954).

Additional material. 1 spm., SMF 17446, "Johan Ruud" St. 476, 70 °01.43’N 30°47.70’E, NE Atlantic, N Norway, Varangerfjord, SE Skallne, 10 May 2006, epibenthic sledge, 232 m, ded. & ded. C. d'Udekem d'Acoz. 1 spm., SMF 17467, "Johan Ruud" St. 308, 70 °57.90’N 25°27.05’E, NE Atlantic, N Norway, Magerøysundet, Risvikneset, 14 April 2005, dive, 20 m, leg. & ded. C. d'Udekem d'Acoz. 1 spm., SMF 17478, "Johan Ruud" St. 298, 70 °58.73’N 25°17.78’E, NE Atlantic, N Norway, Magerøysundet, Stikkelsvågnaeringen, 13 April 2005, dive, 20 m, leg. & ded. C. d'Udekem d'Acoz. 1 spm. (af), SMF 17479, "Johan Ruud " St. 299, 70°59.26’N 25°19.99’E, N E Atlantic, N Norway, Magerøysundet, Stikkelsvågnaeringen, 13 April 2005, dive, 20 m, leg. & ded. C. d'Udekem d'Acoz. 1 spm. (af), SMF 17481, "Johan Ruud" St. 310, 70 °59.35’N 25°20.34’E, NE Atlantic, N Norway, Stikkelsvågnaeringen, 14 April 2005, dive, 20 m, leg. & ded. C. d'Udekem d'Acoz. 2 spms. (juv.), SMF 17504, "Johan Ruud" St. 734, 69 °52.04’N, 18°52.82’E, NE Atlantic, N Norway, Kvalsund i Kårvik, 7 October 2002, epibenthic sledge, 60 m, leg. & ded. C. d'Udekem d'Acoz. 1 spm. (juv.), SMF 17513, "Johan Ruud" St. 733, 69 °52.04’N, 18°52.82’E, NE Atlantic, N Norway, Kvalsund i Kårvik, 7 October 2002, epibenthic sledge, 60 m, leg. & ded. C. d'Udekem d'Acoz. 1 spm., SMF 17514, " Jan Mayen " St. 196, 78 °52.2’N 22°13.4’E, Arctic Ocean, Svalbard, Hinlopen, 23 September 2003, Sneli sledge, 120 m, leg. & ded. C. d'Udekem d'Acoz. 2 spms. (juv.; 1 cs, 1 af), SMF 17521, " Jan Mayen " St. 196, 78 °52.2’N 22°13.4’E, Arctic Ocean, Svalbard, Hinlopen, 23 September 2003, Sneli sledge, 120 m, leg. & ded. C. d'Udekem d'Acoz. 2 spms., SMF 17527, " Jan Mayen " St. 204, 78 °40.6’N 21°23.8’E, Arctic Ocean, Svalbard, S Hinlopen, 23 September 2003, Sneli sledge, 50 m, leg. & ded. C. d'Udekem d'Acoz. 1 spm., SMF 18853, St. HP-376, 44 ° 59.136'N 67°1.944'W, NE Pacific, Canada, St. Andrews, Passamaquoddy Bay, silt substrate, 70 m,trawl, 7 August 2008, leg. E. Corstorphine & C. Carr, ded. C. Carr. 1 spm., SMF 18860, St. HP-386, 45 °0.402'N 67°2.502'W, NE Pacific, Canada, St. Andrews, Passamaquoddy Bay, silt substrate, 10 m, trawl, 14 August 2008, leg. E. Corstorphine & C. Carr, ded. C. Carr. 1 spm. (cs), SMF 18895, "G.O. Sars" St. 2669, 71 °14.90’N 26°56.02’E, NE Atlantic, N Norway, 18 August 2007, 281.6 m, ded. A. Sikorski.

Diagnosis. Elytra at outer lateral margin with long, at posterior margin with short papillae; microtubercles conical to cylindrical, distally simple, bifid, or multifid, becoming larger towards posterior margin; macrotubercles scattered on surface and near posterior margin, cylindrical and distally branched multifid, or spiny.

Description (based on smaller specimen out of two, SMF 17527). Body with 36 segments. At anterior end (Fig. 3 A), prostomium bilobed, cephalic peaks absent (small peaks might be present in other specimens); ceratophore of median antenna in anterior notch, lateral antennae inserted ventrally, styles of antennae papillate, abruptly tapering subdistally; anterior pair of eyes situated dorsolaterally at widest part of prostomium, posterior pair dorsally near hind margin of prostomium; palps distinctly papillate, tapering.

Tentaculophores inserted laterally to prostomium, each with two notochaetae and a dorsal and ventral tentacular cirrus, styles of cirri papillate, abruptly tapering subdistally. Second segment with first pair of elytra, biramous parapodia, and long buccal cirri. Following segments with short, tapering, slightly papillate or smooth ventral cirri.

Fifteen pairs of elytra, covering dorsum, on segments 2, 4, 5, 7, then on every second segment to 23, 26, 29, 32; last four segments cirrigerous; elytra at outer lateral margin with long, at posterior margin with short papillae; microtubercles conical to cylindrical, distally simple, bifid, or multifid, becoming larger towards posterior margin; macrotubercles scattered on surface and near posterior margin, cylindrical and distally branched multifid, or spiny (Fig. 3 B,C). Cirrigerous segments with distinct dorsal tubercles; dorsal cirri with cylindrical cirrophore, style papillate, abruptly tapering subdistally.

Parapodia biramous; notopodia with elongate acicular lobe; neuropodia with elongate prechaetal acicular lobe with short, digitiform supra-acicular process; neuropodial postchaetal lobe shorter than prechaetal lobe, rounded; tips of noto- and neuroacicula penetrating epidermis (Fig. 3 D). Notochaetae stouter than neurochaetae, with distinct rows of spines and blunt tip (Fig. 3 E); neurochaetae all unidentate with distinct rows of spines, leaving rather long bare part distally, tip slightly falcate (Fig. 3 F–H).

Measurements. Specimens from Svalbard (SMF 17527): small specimen, cs, L 23 mm, W 6 mm (excl. chaetae) for 36 segments (Fig. 3 A–H); large specimen, cs, L 45 mm, W 12 mm (excl. chaetae) for 37 segments.

Specimens of Eunoe oerstedi can get very large in Arctic waters as is the case for E. nodosa. A rather large specimen found by D. Eibye-Jacobsen (pers. comm.) in Arctic Canada reached a length of 63 mm and a width of 22 mm (excl. chaetae). According to Pettibone (1963) specimens can grow even larger: length up to 80 mm, width 30 mm (incl. chaetae) for up to 42 segments.

Remarks. Eunoe nodosa and E. oerstedi have often been confused in the past (see also Pettibone 1954), but they differ in the shape and distribution of their elytral tubercles (Figs. 2 B–D, 3B–C). In E. nodosa microtubercles are mostly low, semi-globose, and with nodular papillae distally; macrotubercles occur in a row near the posterior margin, they are usually conical to cylindrical, and show nodular papillae distally. In E. oerstedi, however, macrotubercles are scattered on the surface and near the posterior margin, they are all distally branched multifid or spiny; microtubercles are much more erect than in E. nodosa, being conical to cylindrical and distally simple, bifid, or multifid.

At first glance Eunoe oerstedi and Acanthicolepis zibrowii n. sp. (see below) might be confused, since they show some similarities in their elytra. But they differ clearly in two important generic characters, i.e. the number of pairs of elytra and the shape of the tip in the neurochaetae: E. oerstedi has 15 pairs of elytra and neurochaetae with exclusively unidentate tip, while A. zibrowii n. sp. has 18 pairs and mainly bidentate neurochaetae with stout secondary tooth and only some unidentate neurochaetae.

Distribution and habitat. Arctic Ocean, North Atlantic and North Pacific; from shallow waters to 940 m (see Pettibone 1963).