Cossura keablei, Zhadan, 2015

Zhadan, Anna, 2015, Cossuridae (Annelida: Polychaeta: Sedentaria) from Australian and Adjacent Waters: the First Faunistic Survey, Records of the Australian Museum 67 (1), pp. 1-24 : 13-15

Cossura keablei n. sp.

Figs 9–11

Type locality. Fiji, Suva Harbour.

Type material. Holotype anterior fragment 0.5 mm wide, 8.75 mm long, with 24 thoracic chaetigers; Fiji, Suva Harbour (18°8'S 178°25'E), Oct. 1998, coll. Shirley Mohammed, stn.18 A, W.45623.

Paratypes 2 specimens, Philippines, west coast of Marinduque Island (13°30'N 121°30'E), Dec. 1996, coll. MARCOPPER staff, Stn. 30, W.27171; 1 complete specimen, SEM pin mount, Philippines, west coast of Marinduque Island (13°30'N 121°30'E), Dec. 1996, coll. MARCOPPER staff, Stn. 30, W.42862 ; 1 specimen, Fiji, Suva Harbour (18°8'S 178°25'E), Benthic survey, Oct. 1998, coll. Shirley Mohammed, stn.18 A, W.46099 .

Additional material examined. Philippines. 3 specimens, West coast of Marinduque island (13°30'N 121°30'E), W.27175 .— Fiji. 3 specimens, stn.19B, Suva & Nadi Harbour, Benthic survey, Oct. 1998, coll. Shirley Mohammed, W. 43358 ; 1 specimen, Suva & Nadi Harbour, Benthic survey, Oct. 1998, coll. Shirley Mohammed, stn.7B, W.43355 ; 1 specimen, Suva & Nadi Harbour, Benthic survey, Oct. 1998, coll. Shirley Mohammed, stn. 31A, W.43354 ; 9 specimens, Suva & Nadi Harbour, Benthic survey, Oct. 1998, coll. Shirley Mohammed, stn.34B, W.43357 .

Diagnosis. Prostomium rectangular or trapezium-shaped, with round or almost straight anterior margin, flattened dorsoventrally. 22–26 thoracic chaetigers; anterior segments without glandular pads. Branchial filament arising from chaetiger 3. All chaetae capillary of similar thickness. Thoracic chaetigers with 6–9 chaetae per ramus, abdominal chaetigers with 2–3 thin capillary chaetae in each ramus. Pygidium without cirri and other appendages.

Description. Body length of complete specimen (W.42862) about 4.5 mm, width 300 μm, consisting of 46 chaetigers. 22–26 thoracic chaetigers. Border between regions unclear, abdomen differs by position of parapodia on the middle of segment, less number of chaetae in bundles and longer segments ( Figs 9A , 10A , 11F ). Anterior segments without glandular pads ( Fig. 9C ).

Prostomium rectangular or trapezium-shaped, with round or almost straight anterior margin, flattened dorsoventrally ( Figs 9C,D , 10C,D , 11A,B ). Prostomial furrow well defined, posterior ring wider than prostomium, shorter or same length with peristomium, with midventral notch ( Figs 9C,D , 10C , 11B ). Branchial filament arising from anteromedial part of chaetiger 3 ( Figs 9C , 10C , 11B ).

Chaetiger 1 with uniramous parapodia, all next segments with biramous parapodia with widely arranged rami. All chaetae hirsute capillaries; arranged in two rows. First chaetiger bearing 8–10 chaetae, next segments 6–9 chaetae in each ramus, neurochaetae in anterior rows slightly thicker than other chaetae ( Figs 10A,B,D , 11B–E ). Lateral organs seen behind chaetae fascicles beneath notopodia ( Fig. 11B ). In abdominal region segments having two, rarely three thin, non-hirsute chaetae in each ramus ( Figs 10E , 11F ).

Pygidium without cirri and other appendages (probably lost) ( Fig. 10F ).

Etymology. This species has been named in honour of Steven Keable, in recognition of his great effort to maintain and improve the collection of invertebrates of Australian museum.

Remarks. Few cossurid species also have the branchial filament on chaetiger 3 and no acicular chaetae in abdomen: Cossura candida Hartman, 1955 , C. bansei Hilbig , C. chilensis Hartmann­Schröder, 1965 , C. bansei Hilbig, 1996 , C. dayi Hartman, 1976 , C. delta Reish 1958 and C. consimilis Read, 2000 . Cossura keablei differs from them by the trapezium shape of prostomium and by having 2–3 capillary chaetae per ramus in the abdominal region. Moreover, C. chilensis has 19 thoracic chaetigers, C.delta has 15–18 thoracic chaetigers which is less, and C.consimilis has 27–31 thoracic chaetigers which is more than in C. keablei . Cossura brunnea Fauchald, 1972 has trapezium prostomium but differs by less number of thoracic chaetigers, dark pigment pattern over the median and posterior regions of its body, and having three long anal cirri.

Figures

Figure 9. Cossura keablei n. sp. W.45623, holotype, stereomicroscope. B–D stained with methylen blue. (A) general ventral view; (B) transitional region; (C) anterior end, dorsal view; (D) anterior end, ventrolateral view. Scale bars: A = 1 mm, B–D = 300 μm.

Figure 10. Cossura keablei n. sp. Compound microscope. (A) W.27171, paratype, general view, anterior end from lateral, then from dorsal; (B) W.46099, paratype, lateral view; (C) W.27175, anterior end, dorsal view; (D) W.27171, paratype, anterior end, lateral view; (E) W.27171, paratype, abdominal parapodia; (F) W.27171, paratype, posterior end, dorsolateral view. Scale bars: A, B = 500 μm, C, D = 200 μm, E, F = 100 μm.

Figure 11. Cossura keablein. sp. Paratype, W.42862, SEM.(A) general view; thorax and beginning of abdomen; anterior end:posterolateral view, abdomen: ventral view; (B) anterior end, lateral view (arrow indicates lateral organ); (C) notopodia of chaetiger 3; (D) neuropodia of chaetiger 4; (E) parapodia of chaetigers 18–20; (F) abdominal parapodia. Scale bars: A, B = 100 μm, C–F = 20 μm.