Austropolaria magnicirrata, Neal, Barnich, Wiklund & Glover, 2012

Neal, L., Barnich, R. & Wiklund, H, 2012, A new genus and species of Polynoidae (Annelida, Polychaeta) from Pine Island Bay, Amundsen Sea, Southern Ocean-a region of high taxonomic novelty, Zootaxa 3542, pp. 80-88 : 83-87

Austropolaria magnicirrata n. gen. n. sp.

Fig. 2 A–G , Fig. 3 A–E and Fig. 4 A–E (holotype)

Holotype, NHM 2012.92

Paratypes 1&2, NHM 2012.93–94

Paratype, SMF 21299

Material Examined. BIOPEARL II Expedition 2008, cruise RRS James Clark Ross 179: holotype NHM 2012.92 ( BIO4 -EBS-1B-Supra, BIO4, 74.35865°S, 104.73444°W, 06 March 2008, 1415 m) Southern Ocean , Amundsen Sea, Pine Island Bay ; paratype SMF 21299 St. BIO4 (74.35865°S, 104.73444°W, 06 March 2008 ,1415 m) , paratypes 1& 2 NHM 2012.93-94 BIO5 (74.11842°S, 105.83757°W, 09 March 2008, 1477 m; 73.888646°S, 106.29387°W, 09 March 2008, 1148 m), Southern Ocean , Amundsen Sea, Pine Island Bay .

Additional material: 405 specimens were examined in total, all of which conformed with the type specimen.

Description (based on holotype, NHM 2012.92)

Body with 20 segments. Anterior end ( Fig. 2A ) of prostomium bilobed, without frontal filaments and eyes; ceratophore of median antenna near posterior margin, style of median antenna missing; palps smooth, tapering, reaching 1 ½ times the length of the everted pharynx.

Tentaculophores inserted laterally to prostomium, achaetous, each with a small, short dorsal and a larger, longer ventral tentacular cirrus. Pharnyx everted, with seven pairs of papillae distally, jaws with main fang, but without denticles. Second segment with first pair of reduced, knob-like elytrophores and biramous parapodia. ( Fig. 2A ).

Nine pairs of reduced, knob-like elytrophores (presence of elytra not confirmed), on segments 2, 4, 5, 7, 9, 11, 13, 15, 17; last three segments cirrigerous. Cirrigerous segments with large dorsal cirri with very prominent cirrophores of two kinds: 1) short, conical and 2) elongate, cylindrical, bent distally; styles of dorsal cirri all missing, some free in vial, long, smooth, tapering; dorsal tubercles absent. ( Fig. 2C ). Ventral cirri present from segment 3 to last segment, inserted subdistally on neuropodium; style smooth, tapering, not reaching tip of neuropodium ( Fig. 2D ).

Parapodia biramous; noto- and neuropodia with elongate acicular lobe; tips of noto- and neuroacicula penetrating epidermis ( Fig. 2D ). Notochaetae stout, serrated along convex margin, tip more or less blunt; neurochaetae more slender, with distal part flattened and serrated along lateral margins, tip unidentate, blunt to pointed. ( Fig. 2E–G ).

Posterior end with ventral keel, reaching back to segment 17, pygidium with dorsal anus, styles of anal cirri missing ( Fig. 2B ).

Measurements. Holotype (NHM 2012.92): cs, L 16 mm, W 7 mm for 20 segments ( Fig. 2A–G ); paratype (SMF 21299): cs, L 14 mm, W 7 mm for 19 segments; paratype 1 (NHM 2012.93): cs, L 17 mm, W 8 mm for 20 segments; paratype 2 (NHM 2012.94): cs, L 14 mm, W 6 mm for 19 segments. Additional specimens cs, L 4–6 mm, W 3–4 mm for 18–19 segments.

Distribution and habitat. Southern Ocean, Amundsen Sea, Pine Island Bay, 1000–1500m.

Etymology. The species name magnicirrata (Latin for large cirrus) refers to the large dorsal cirri with prominent cirrophores.

Remarks. Austropolaria magnicirrata n. gen. n. sp. is remarkable within the Macellicephalinae for its 20 segments, nine pairs of reduced elytrophores, the distinct ventral keel and for its prominent cirrophores which at first glance could be mistaken for elytrophores. Two types of prominent cirrophores are found: shorter, conical and elongate, cylindrical cirrophores which are distally bent. The number and position of elongate cirrophores is varying in the specimens investigated here: e.g. only one elongate cirrophore on segment 6 (left side) in the holotype (NHM 2012.92) and on segment 16 (right side) in paratype (SMF 21299), but eight cirrophores distributed along the body in paratype 1 (NHM 2012.93) or two at segments 3 and 6 (left side) in paratype 2 (NHM 2012.94).

As discussed above Austropolaria magnicirrata n. gen. n. sp. might be confused with Bathypolaria carinata Levenstein, 1981 , which shows also a ventral keel and the two types of large cirrophores as confirmed by our investigation of specimens from Nazaré Canyon. The new species differs from B. carinata by the higher number of segments and elytrophores.

Ecology: At present Austropolaria magnicirrata n. gen. n. sp. is only known from Pine Island Bay in Amundsen Sea, where its distribution is limited to deeper sites (1000 m and 1500 m depth) and was not found at shallower 500 m stations. In total 405 specimens —adults and juveniles were collected. This species was particularly abundant (n=260) at basin location BIO4 at 1500m and less so at basin location BIO5 (n=89) (see Fig.1 ). Both sites are located near the Pine Island glacier. These deep basins had previously been interpreted as an evidence of past erosion by sub-glacial meltwater. Austropolaria magnicirrata n. gen. n. sp. represents yet another deep-water species of Macellicephalinae , strengthening its position as a preliminary deep- water group and providing further link between deep-shelf Antarctic habitats and true deep-sea.

DNA: Sequences of Austropolaria magnicirrata n. gen. n. sp. are published at NCBI Genbank with accession numbers 16S JX863896 and 18S JX863895 and voucher specimen for the sequences is deposited at the Natural History Museum in London, UK, voucher number NHM 2012.95.

Figures

FIGURE 1. Pine Island Bay and the position of epibenthic sledge stations sampled during the BIOPEARL 2 (JR 179) cruise. (modified from Kaiser et al. (2009)

FIGURE 2. Austropolaria magnicirrata n. gen. n. sp., holotype NHM 2012.92. (A) anterior end, dorsal view; left dorsal cirrus of segment 3 and styles of median antenna and left tentacular cirri missing, parapodia of left side damaged; (B) posterior end, lateral view; parapodia not figured, styles of dorsal and anal cirri missing; (C) elongate cirrophore of segment 6, reduced elytrophore of segment 7, and conical cirrophore of segment 8, left side; (D) right cirrigerous parapodium of segment 6, posterior view; style of dorsal cirrus missing; (E) long notochaeta; (F) distal half of middle neurochaeta; (G) tip of same. (Scales A–C = 2 mm; D = 1 mm; E, F = 250 µm; G = 100 µm).

FIGURE 3. Austropolaria magnicirrata n. gen. n. sp., holotype NHM 2012.92 (a) live specimen, dorsal view; (b) preserved specimen, dorsal view; (c) detail of prostomium in dorsal view, style of medina antenna and styles of tentacular cirri missing, damaged; (d) extended pharynx with proboscisidial papillae; (e) pygidial keel, ventral view (Scales: A–C = 1 mm; D–E = 200 µm).

FIGURE 4. Austropolaria magnicirrata n. gen. n. sp., holotype NHM 2012.92 (a) cirrophores—ci and elytraphores—el on segments 3–6, elytra and styles of dorsal cirri missing, damaged; (b) parapodium; (c) notochaeta, SEM image; (d) notchaetae; (e) neurochaetae. (Scales: A = 200 µm; B = 1mm; C = 20 µm; D = 125 µm; E = 50 µm). Footnotes: In the ‘Material’ section, complete specimens are indicated by ‘cs’. Measurements: length (L) is measured from the anterior margin of the prostomium to the posterior border of the last segment (pharynx not included, if everted), width (W) is taken at the widest segment, including parapodia but excluding chaetae.