Polyeunoa laevis McIntosh 1885

Polyeunoa laevis McIntosh, 1885

(Figs. 1 A–H, 2A–D)

Polyeunoa laevis McIntosh, 1885: 76, pl. 12 fig. 2, pl. 20 fig. 8, pl. 7A figs. 12, 13; Bergström (1916): 288, pl. 3 fig. 7; Fauvel (1936): 12; Monro (1936): 102 [part]; Uschakov (1962): 177; Hartman (1964): 42, pl. 12 figs. 5–7 [part]; Hartman (1967): 38; Hartman (1978): 136; Pettibone (1969): 46, fig. 1; Orensanz (1976): 11; Hartmann-Schröder (1983): 261; Knox & Cameron (1998): 34, figs. 69–72; Barnich et al. (2012): XXX.

Enipo rhombigera Ehlers, 1908: 47, pl. 4 figs. 1–12; Ehlers (1913): 449.

Polyeunoe (sic!) dubia Hartmann-Schröder, 1965: 69, figs. 13–17 [new synonymy].

Polynoe thouarellicola Hartmann-Schröder, 1989: 207, figs. 1–11.

Polynoe antarctica: Knox & Cameron (1998): 35, figs. 73–76 [not P. a n t a rc t i c a Kinberg, 1858, see below].

Type material. Polyeunoa laevis: Syntypes BMNH 1885.12.1.55 (2 cs, 8 af & numerous fragments), “Challenger“ Exp., St. 145A, off Prince Edward Island, 46°41’S 38°10’E, 27 December 1873, 310 fms, volcanic sand.

Enipo rhombigera: Lectotype [designated herein, spm. described and figured in detail in Ehlers 1908] ZMB 10581 (cs), Deutsche Tiefsee-Exp. 1898/1899, St. 131, E of Bouvet Island, 54°28’S 3°30’E, 457 m, volcanic sand. Paralectotypes ZMB 5759 (numerous spms.), Deutsche Südpolar-Exp. 1902/1903, Winterstation, 350– 385 m.

Polyeunoe dubia: Holotype ZMH P- 1527 (af) & paratype ZMH P- 15249 (af), Mar Chile I Exp., St. X1, Gulf of Concorado (S Chile), 21 March 1960, 170 m, fine sand with stones, mud and detritus.

Polynoe thouarellicola: Holotype ZMH P- 19360 (cs) & paratype ZMH P- 19364 (af), ANT VI/2 Exp., RV “Polarstern“, St. 12/227, Elephant Island, 61°91.8’S 56°11’W, 16 December 1987, 387– 426 m, bottom trawl, on Thouarella sp. (gorgonarian coral).

Additional material. Off coast of Argentina / S of Falklands: 2 spms., SMF 19955, “Walter Herwig” 15, St. 234, E Santa Vitória do Palmar, 35°14’S 52°28’W, 12 June 1966, 200 m. 21 spms., SMF 19956, “Walther Herwig” 15, St. 245, E Mar de Ajó, 36°49’S 54°02’W, 14 June 1966, 600 m, associated with octocorals. 2 spms., MACN-In 39410, “Walther Herwig” 15, St. 245, E Mar de Ajó, 36°49’S 54°02’W, 14 June 1966, 600 m, associated with octocorals. 1 spm., SMF 20035, “Walther Herwig” 15, St, 246, E Mar de Ajó, 36°48’S 54°03’W, 14 June 1966, 500 m. 1 spm. (mf), SMF 19958, “Walther Herwig” 15, St. 306, E Comodoro Rivadavia, 45°46’S 60°19’W, 25 June 1966, 200 m. 1 spm., SMF 19957, “Walther Herwig” 15, St. 340, S Malvinas Islands (Falklands), 53°47’S 58°46’W, 1 July 1966, 165 m.

Weddell Sea (Collection of M.C. Gambi): 14 spms., EASIZ I Exped., ANT XIII/3, St. 39/001, NE Kap Norvegia, 71°03.10’S 11°25.50’W, 5 February 1996, bottom trawl, 462–481 m, on gorgonarian coral. 7 spms., EASIZ I Exped., ANT XIII/3, St. 39/005, SW Kap Norvegia, 71°40.49’S 12°41.70’W, 6 February 1996, epibenthic sledge, 254– 239 m, on gorgonarian coral. 2 spms., EASIZ I Exped., ANT XIII/3, St. 39/011, between Vestkap and Halley, 73°22.60’S 21°10.60’W, 13 February 1996, bottom trawl, 338– 333 m, on gorgonarian coral. 5 spms., EASIZ I Exped., ANT XIII/3, St. 39/012, between Vestkap and Halley, 73°18.10’S 21°10.10’W, 13 February 1996, bottom trawl, 459– 457 m, on gorgonarian coral. 1 spm., SMF 21633, EASIZ I Exped., ANT XIII/3, St. 39/014, between Vestkap and Halley, 73°36.1’S 22°35.7’W, 14 February 1996, small dredge, 850–889 m, on Primnoisis sp., ded. M.C. Gambi. 10 spms., EASIZ I Exped., ANT XIII/3, St. 39/015, between Vestkap and Halley, 73°42.00’S 22°30.50’W, 15 February 1996, bottom trawl, 446– 428 m, on gorgonarian coral. 3 spms., EASIZ I Exped., ANT XIII/3, St. 39/016, between Vestkap and Halley, 73°53.40’S 22°26.90’W, 15 February 1996, bottom trawl, 246– 242 m. 3 spms., EASIZ I Exped., ANT XIII/3, St. 39/017, between Vestkap and Halley, 73°18.00’S 21°09.90’W, 16 February 1996, bottom trawl, 468– 465 m, on gorgonarian coral. 3 spms., EASIZ I Exped., ANT XIII/3, St. 39/026, W of Kap Norvegia, 71°29.30’S 14°18.6’W, 24 February 1996, small dredge, 216– 222 m. 5 spms., EASIZ I Exped., ANT XIII/3, St. 39/032, NW of Atka, 70°28.90’S 8°15.1’W, 4 March 1996, small dredge, 286– 283 m, on Primnoisis sp. and Dasystenella sp. 5 spms., EASIZ II Exped., ANT XV/3 St. 48/078, Drescher Inlet, 72°51.1’S 19°15.1’W, 3 February 1998, bottom trawl, 391 m.

Ross Sea (Collection of M.C. Gambi): 17 spms., Terra Nova Bay, Road Bay, st. E 2, 24 December 1989 dredge, 100 m depth.

Diagnosis. Prostomium with cephalic peaks poorly developed or absent. Antennae and cirri very long, median antenna much longer than lateral antennae. Tip of neuropodial acicular lobe not extended to supra-acicular process. Neurochaetae mainly unidentate, some minutely bidentate. Ventral cirri long, reaching to tip of neuropodia in anterior segments.

Description (based on additional specimen in good condition, SMF 21633, Fig. 1, and paralectotype of Enipo rhombigera ZMB 5759, Fig. 2).

Prostomium bilobed, with indistinct cephalic peaks (Fig. 1 A); ceratophore of median antenna in anterior notch, style smooth, tapering, very long (reaching back to segment 14 in paratype of E. rhombigera, Figs. 2 A,B); lateral antennae inserted ventrally to median antenna, styles smooth, tapering; anterior pair of eyes situated dorsolaterally at widest part of prostomium, posterior pair dorsally near hind margin of prostomium; palps tapering.

First or tentacular segment with a pair of tentaculophores inserted laterally to prostomium, without notochaetae, but with a dorsal and a ventral tentacular cirrus, styles smooth, very long, tapering (Fig. 2 B). Second or buccal segment with first pair of elytra, biramous parapodia and long tapering ventral or buccal cirri. Following segments with ventral cirri rather long, reaching to tip of neuropodium in anterior segments, getting shorter more posteriorly (Fig. 1 C).

Fifteen pairs of elytra, on segments 2, 4, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 26, 29 and 32 (in other specimens additional, sporadically and irregularly arranged pairs of elytra present after segment 32); elytra nearly covering dorsum in anterior body region, becoming smaller more posteriorly; usually smooth, occasionally anterior elytra with few scattered marginal papillae near anterior margin (Figs. 1 B, 2B,C). Cirrigerous segments with small, rather indistinct dorsal tubercles in anterior segments, tending to disappear more posteriorly; dorsal cirri with cylindrical cirrophore, styles smooth, very long and tapering (Fig. 2 A–D).

Parapodia biramous; notopodia and neuropodia with prominent acicular lobe, tip of neuropodial acicular lobe not extended to supra-acicular process; tips of noto- and neuroacicula penetrating epidermis (Fig. 1 C). Notochaetae few, about as stout as neurochaetae, with faint rows of spines and blunt tip (Fig. 1 D,E); neurochaetae more numerous, with distinct rows of spines distally, and mostly with unidentate tip, occasionally bidentate, with minute secondary tooth (often abraded) (Fig. 1 F–H).

Dorsal side of segments with or without transverse or longitudinal pigmentation (in ethanol).

Measurements. Specimens figured here: cs in two fragments, L 55 mm, W 6 mm for 64 segments (Fig. 1, SMF 21633); cs, L 60 mm, W 7 mm for 62 segments (Fig. 2, ZMB 5759, paratype of E. rhombigera). Largest complete syntype of P. l a e v i s (BMNH 1885.12.1.55): L 38 mm, W 7 mm for 68 segments.

Remarks. As noted already by several authors, like Bergström (1916), Pettibone (1969), and Stiller (1996), Polyeunoa laevis shows a number of variable characters. Examination of several specimens from the same station (ANT XIII/3 St. 0019) confirmed that not only the number and insertion of elytra and the expression of the cephalic peaks are variable characters, but also the presence and extent of pigmentation on the dorsum and the presence or absence of dorsal tubercles are subject to individual variability. However, characters which are constant and clearly allow the identification of P. la ev i s are the presence of neuropodia with tip of acicular lobe not extended to supraacicular process and neurochaetae all unidentate or mostly unidentate and some minutely bidentate. Additional molecular characters might be helpful, but such a study is beyond the scope of this paper (see also remark related to the genus Polyeunoa above).

If specimens of P. laevis show only 15 pairs of elytra, differentiation from Neopolynoe antarctica (Kinberg, 1858) n. comb. (see below) might be difficult. However, in the latter species the anterior pair of eyes is situated slightly in front of the widest part of the prostomium, the cephalic peaks are well developed, and the tip of the acicular neuropodial lobe, is extended to a thick, stout supra-acicular process (Table 2).

Polyeunoa laevis and Parapolyeunoa flynni (Benham, 1921) n. comb. have often been confused in the past. As we demonstrate below, differentation of both species is rather easy, since Parapolyeunoa flynni is mainly characterised by the presence of distinct cephalic peaks, a short, digitiform supra-acicular process, short ventral cirri and distinctly bidentate neurochaetae (Table 2).

Distribution. Widely distributed in the SW Atlantic (northwards up to Buenos Aires) and the Magellan, Sub- Antarctic and Antarctic regions, in 35–2450 m depth, often associated with gorgonarian corals, e.g., with Thouarella sp., Primnoisis sp. or Dasystenella sp. (see also Stiller 1996, Barnich et al. 2012)