Polycirrus twisti Potts, 1928

Glasby, Christopher J. & Hutchings, Pat, 2014, Revision of the taxonomy of Polycirrus Grube, 1850 (Annelida: Terebellida: Polycirridae), Zootaxa 3877 (1), pp. 1-117 : 107-108

Polycirrus twisti Potts, 1928

Fig. 60a–c

Polycirrus twisti Potts, 1928: 689–700 , fig. 212.

Type locality. Suez Canal.

Material examined. HOLOTYPE: CUMZ AN 1.1930 , Suez Canal, St. K. O, coll. Cambridge Expedition to the Suez Canal, 18.x.1924 .

Description. Holotype poorly preserved with body wall damaged, chaetae present mainly intact, yellowish brown in colour, consists of fragments of probably two individuals. First individual anterior fragment 4.0 mm long, 1.0 mm wide excluding buccal tentacles, with eight segments. Second individual with anterior fragment 12 mm long, 1.2 mm wide for about 21 segments but posterior portion damaged and poorly preserved. Median fragment 30 mm long, 1.2 mm wide. Two posterior fragments with following dimensions: 12 mm long, 1.2 mm wide, and 20 mm long, 1.2 mm wide, only anterior 5 mm well preserved. Sex unknown.

Dorsum anteriorly tessellated. Venter anteriorly with mid-ventral groove and discrete ventro-lateral pads; pads incised and tessellated.

Buccal tentacles numerous, of two types: (1) cylindrical, thickened distally and distinctly grooved and (2) cylindrical, uniformly thin and weakly grooved, both arising dorsally on prostomial ridge. Prostomial ridge distinctly curved, extending laterally along anterodorsal base of upper lip. Upper lip trefoiled with lateral, blindly ending, enclosed diverticulae, margin of medial lobe convoluted, glandular; oral surface glandular, ciliated, with grooves leading to mouth. Inner lower lip oblong hidden by upper lip, ridged; outer region flat, shield-like, subtriangular and pointing toward mouth, inflated, ridged and grooved, extending posteriorly to segment 3. Achaetous segments visible dorsally but obscured by expanded outer lower lip ventrally.

Notochaetigerous segments 30, extending to segment 32 (approx. according to Potts (1928)). Notopodia moreor-less rectangular, paddle-shaped, prechaetal lobe low, postchaetal lobe digitiform, longer than prechaetal. Notochaetae within a chaetiger consisting of two types (chaetiger 12 examined), pinnate, posteriorly same form as those anteriorly; secondary notochaetae in all chaetigers smooth, narrowly winged, slender, uniformly tapered ( Fig. 60a, b ). Neurochaetae beginning on segment 3 (according to description, but this seems unlikely). Posterior neuropodial tori erect pinnules. Uncini with long neck and concave base (Type 2), posterior ones with shorter neck and straight base, teeth above main fang arranged in multiple series (posterior ones), subrostral process absent (posterior ones) ( Fig. 60c ).

Nephridial papillae present, globular, post-gular ones flatter. Post-gular membrane nephridial papillae present, extending from segment 5 over an undeterminable number of anterior chaetigers; situated at base of notopodia. Pygidium simple rosette.

Comments. The University Museum of Zoology, Cambridge, has a policy of not sending material in the mail and thus the types had to be examined in the Natural History Museum, London. Facilities for drawing the anterior end were not available; thus, the anterior end of the species unfortunately remains unfigured. We have reproduced Potts’ (1928) figure of the chaetae here.

Figures

FIGURE 60. Polycirrus twisti Potts. a, b. Notochaetae, smooth and pinnate. c. Neurochaetae. (Modified after Potts, 1928; no scales provided in original).