Polycirrus arcticus Sars 1865

Polycirrus arcticus Sars, 1865

Fig. 7a–f

Polycirrus arcticus Sars, 1865: 14; Holthe, 1986b: 147–148.

Leucariste albicans Malmgren, 1865: 390–391.

Type locality. Vadsø, Norway.

Material examined. SYNTYPES of Polycirrus articus ZMO C3204 Norway, Vadsø, lg. Danielsen. SYNTYPES of Polycirrus albicans SMNH 1131 ‘ Spetsb Naygatia’, 182 m (100 fms), A.J. Malmgren SMNH 6741; 1127 ‘ Spetsb Crassob’, 91 m (50 fms), ‘ Goes et Smitt’ SMNH 6743; 1124 ‘ Spetsb Wydels’, 73 m (40 fms), 1126 ‘ Goes et Smitt’ SMNH 6738 (designated here as LECTOTYPE); 1125 ‘ Spetsb Wahlenb’, 92 m (50 fms), A.J. Malmgren SMNH 6737; ZMO C1536 ‘ Kingsbay Spitzbergen, Lerbund’ 220 m (120 fms), viii.1861 (all places on the island of Spitsbergen, Svalbard Archipelago, Norway, Arctic Ocean).

Description. Syntypes of P. articus in poor condition, consisting of several complete specimens up to 30 mm long and 2 mm wide, colourless, virtually impossible to count number of chaetigers as segmentation indistinct, notopodia and neuropodia small and indistinct, ventral pads not differentiated. Following description based upon P. albicans (SMNH 6738) which consists of six individuals, the largest and best preserved specimen is described in detail and designated the lectotype; the other five lots (SMNH 6741, SMNH 6743, SMNH 6738, SMNH 6737 and ZMO C1536) are designated as paralectotypes. Lectotype pale cream in colour, 30 mm long and 2.5 mm wide excluding buccal tentacles, complete with about 46 segments. Sex male.

Body consists of 46–47 segments, 30–35 mm long. Body transparent, red nephridia and intestine visible through body wall according to Sars. Dorsum anteriorly smooth. Venter anteriorly with mid-ventral groove and poorly defined narrow ventro-lateral pads which are longer than wide; pads more-or-less smooth. Mid-ventral groove from segment 3.

Buccal tentacles numerous, of two types: (1) cylindrical, thickened distally, and distinctly grooved and (2) cylindrical, uniformly thin, and weakly grooved, both arising at junction between prostomium and upper lip. Prostomial ridge slightly curved, not extending laterally. Upper lip comprising single (medial) lobe only (folded, semicircular in shape), margin of lobe straight; oral surface glandular, ciliated, with grooves leading to mouth. Inner lower lip oblong (narrow), smooth; outer region flat, shield-like, subtriangular, and pointing toward mouth, ridged and grooved, extending posteriorly to segment 3. Achaetous segments visible dorsally but obscured by expanded outer lower lip ventrally (Fig. 7a).

Notochaetigerous segments 17 or18, extending to segment 19 or 20. Notopodia digitiform (conical with 7–8 capillaries according to Sars), lobes both similar, low and rounded (Fig. 7b). Notochaetae within a chaetiger one type (chaetiger 3 and midbody chaetiger examined), two distinct lengths, smooth, narrowly winged, uniformly tapered, posteriorly same form as those anteriorly (although fewer) (Fig. 7c). Neurochaetae beginning on segment 16. Neuropodial tori erect pinnules, similar along body. Uncini with short neck and straight to convex base (Type 1), teeth above main fang arranged in double transverse series (Sars records only one small tooth above one larger tooth), enlarged median tooth above main fang present, subrostral process present as low protuberance (Fig. 7d–f).

Nephridial papillae present, globular. Pre-gular membrane nephridial papillae present on segments 3 and 4. Post-gular membrane nephridial papillae present, extending from segments 5–14, situated at base of notopodia. Pygidium simple, short rosette.

Comments. Based on a comparison of the syntypes of both P. arcticus and P. albicans, both of which were examined, we confirm Holthe’s (1986b) view that P. albicans is a junior synonym of P. arcticus. The only differences between the two species are that P. albicans has a slightly tessellated anterior dorsum (smooth in P. arcticus), the number of notochaetigerous segments is 17 or 18 in P. arcticus (18 in P. albicans), neurochaetae begin on segment 16 in P. arcticus (15 in P. albicans), the number of post-gular membrane nephridial papillae (14 in P. arcticus; 6 in P. albicans). The differences in the number of nephridial papillae may be related to the sexual maturity of the specimen. The chaetal differences are not considered sufficient to regard them as two distinct species (see Table 1 for typical intraspecific variability ranges in the number of notochaetigerous segments and start of neurochaetae). Holthe (1986b) reports a range of 15–22 notochaetigerous segments for P. arcticus. Although Sars mentions 17 or 18 notochaetigerous segments in the type description, his illustration only shows 14.

Because the syntype specimens of P. arcticus are all in poor condition we have not designated a lectotype. Instead we have designated a lectotype from among the syntype series of P. albicans, and described and illustrated this specimen. The type locality of P. albicans was given as ‘ Spetsbergia’, which is now known as Spitsbergen. It is in the Arctic Circle about 1000 km to the NW of Vadsø, northern Norway, the type locality of P. arcticus.