Polycirrus antarcticus

Polycirrus antarcticus (Willey, 1902)

Fig. 5a–e

Ereutho antarcticus Willey, 1902: 281, Pl. XLII., fig. 6, pl.XLVI, fig. 6.

Polycirrus insignis Gravier, 1907: 54–56, figs 35, 36. New synonym.

Type locality. Antarctica, Cape Adare.

Material examined. HOLOTYPE: Antarctica, Cape Adare, coll. 25.i.1900, washed up after a gale, BMNH 1902:1.8.18, 71°17′ S, 170°14′ E.

HOLOTYPE: Polycirrus insignis A 229, MNHN 1542, Expedition Charcot, Port Charcot, 40 m, coll. 1903–1905, id. 1906, 66°15'S 135°55'E.

Description. Based on holotypes of E. antarcticus and P. insignis. Holotype of E. antarcticus incomplete, 23 chaetigers, 15 mm long, 2.5 mm wide; mature female (from Willey 1902); original description does not mention any damage but some body wall damage now present. Holotype of P. insignis complete, 36 chaetigers, 25 mm long (Fig. 5a, b).

Venter with anterior mid-ventral groove and discrete ventro-lateral pads; pads more-or-less smooth, extending from segment 3 to 10; mid-ventral groove from segment 4 (Fig. 5c).

Buccal tentacles of one type (most are missing), cylindrical, uniformly thin and weakly grooved. Prostomial ridge slightly curved, not extending laterally. Upper lip trefoiled with lateral blindly ending enclosed diverticulae (lateral lobes not as large as medial lobe), margin of medial lobe convoluted; oral surface glandular and ciliated. Inner lower lip oblong; outer region flat, shield-like, oblong, wider than long, tessellated, extending posteriorly to segment 3. Achaetous segments visible dorsally but obscured by expanded outer lower lip ventrally (Fig. 5c, d).

Notochaetigerous segments 11 (10 on one side), extending to segment 13. Notopodia digitiform, lobes both similar, low and rounded (Fig. 5c). Notochaetae within a chaetiger consisting of one type (chaetigers 5 and 10 examined; most chaetae damaged), of two distinct lengths, smooth, narrowly winged (some hirsute at tip as a result of wear), subdistally slightly expanded), posteriorly same form as those anteriorly with blades more striated (Fig. 5e); posterior notochaetae damaged and not illustrated.

Neurochaetae beginning on segment 16. Neuropodial tori erect pinnules, similar along body. Uncini with short neck and straight to convex base (Type 1), single tooth above main fang (in holotypes of both E. antarcticus and P. insignis) or teeth arranged in double transverse series (from type description), subrostral process absent (from type description) or present as low protuberance (observed in holotypes).

Nephridial papillae not observed.

Comments. We have synonymised P. insignis Gravier, 1907 with P. antarcticus (Willey, 1902) after finding no significant differences between the holotypes of both species. In particular, there are no differences in the number of notochaetigerous segments (11 in both species) and minimal difference in the segment having the first neurochaetae (segment 16 in P. antarcticus, segment 14 in P. insignis), which is acceptable intraspecific variability for the genus (see Table 1).

Interestingly, Hessle (1917), Benham (1921), and Holthe (1986b) all considered that P. antarcticus might also be a synonym of E. kerguelensis McIntosh, 1885 (now Polycirrus kerguelensis). However we reject this synonymy since there are significant differences between the two taxa, including the first occurrence of neurochaetae (segment 16 in P. antarcticus, segment 6 in P. kerguelensis) and the form of the notochaetae which are smooth in P. antarcticus and hirsute in P. kerguelensis.