Polycirrus hamiltoni Benham. Smallest 1921

Polycirrus hamiltoni Benham, 1921

Fig. 29a–f

Polycirrus hamiltoni Benham, 1921: 94, pl. 9, fig. 101–106.

Type locality. Macquarie Island, Antarctica.

Material examined. SYNTYPES: 3, AM W611, Australian Antarctic Expedition, Australia, Macquarie Island, Garden Bay, intertidal 54°30ʹ S, 158°57ʹ E (smallest syntype illustrated here).

Additional material examined. 8 specimens, AM W824, Australia, Macquarie Island, 54°30ʹ S, 158°57ʹ E.

Description. Syntypes mainly well preserved with body wall intact, yellowish in colour, 2 complete and 1 incomplete individuals forming type series. Complete individuals 10 mm long (without tentacles), 1 mm wide for 50 segments and 15 mm long (without tentacles) and 1.2 mm wide for 65 segments. Posteriorly incomplete specimen (illustrated here and separated in a microvial from other syntypes) 10 mm long (without tentacles which are missing) and 1 mm wide for 37 segments.

Dorsum anteriorly tessellated. Venter anteriorly with mid-ventral groove and discrete ventro-lateral pads; pads more-or-less smooth, extending from segment 3 to 12. Mid-ventral groove from segment 2 (Fig. 29a).

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 distinctly curved, extending laterally along anterodorsal base of upper lip. Upper lip trefoiled with lateral blindly-ending enclosed diverticula, margin of medial lobe convoluted (slightly); oral surface glandular, ciliated, with grooves leading to mouth. Inner lower lip oblong, raised, ridged; 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.

Notochaetigerous segments 30–34, extending to segments 32–36. Notopodia digitiform anteriorly and moreor-less rectangular posteriorly, prechaetal lobe low, postchaetal lobe digitiform, longer than prechaetal initially, though lobes becoming equal posteriorly (Fig. 29b). Notochaetae within a chaetiger consisting of two types (chaetigers 4, 16 examined), hirsute, subdistally expanded (slightly), posteriorly same form as those anteriorly; secondary notochaetae in all chaetigers pinnate (Fig. 29c, d). Neurochaetae beginning on segment 9. Neuropodial tori erect pinnules, differ along body (uncini arranged in C-shaped row in posterior tori). Uncini with short neck and straight to convex base (Type 1), teeth above main fang arranged in double transverse series (MF:1:∞) enlarged median tooth above main fang present, subrostral process absent (Fig. 29e, f).

Nephridial papillae present, globular. Pre-gular membrane nephridial papillae present on segment 4 only. Postgular membrane nephridial papillae present, extending from segment 5 to 8; situated at ventral base of notopodia (Fig. 29a). Pygidium simple rosette.

Comments. The specimens described here and labelled as syntypes are not the same as those described by Benham (1921). The size and chaetiger numbers do not match. Further, Benham states in his original description that one of the specimens is a mature female, whereas (AM W611) contains two mature males; however, in all other respects the material fits Benham's description and is accepted here as representing syntype material. It is likely that the syntypes were designated after Benham (1921) described the species P. hamiltoni.