Cossura, Webster & Benedict, 1887

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 : 20-24

Cossura sp. A

Fig. 17

Material examined. Anterior fragment, 1.1 mm wide, 7 mm long; New South Wales, east of Gigue (36°59'24"S 150°21'12"E), RV Franklin, FR 1086-06, 11 Dec. 1986, depth 900 m, thick grey mud and abundant worm tubes, W.23618 .

Description. Specimen incomplete, with 28 chaetigers, all thoracic. Big and thick worm with cylindrical body. Coloration uniform yellow. Chaetal bundles arising from anterior borders of segments; in chaetigers 27–28 slightly shifted towards middle parts ( Fig. 17A ). Segments bearing inflations, probably glandular, divided by dorsal groove; segmental borders perpendicular to body axis ( Fig. 17A, C ).

Prostomium short, round, flattened dorsoventrally, triangle from lateral view, with developed prostomial furrow ( Fig. 17C,D ). Posterior ring slightly shorter than peristomium. Beginning from posterior prostomial ring body rapidly expanding in width and in thickness. Branchial filament arising from anterior border of third chaetiger ( Fig. 17C,D ).

Chaetiger 1 with uniramous parapodia, all the next segments with biramous parapodia.All chaetae are capillaries arranged in two distinct rows ( Fig. 17B,D ). Neuropodia bearing 5 thicker chaetae in anterior row and 9–10 thinner ones in posterior row. Notopodia bear 6–7 chaetae in each row, all notochaetae as thick as posterior neuropodial chaetae ( Fig. 17B ). Posterior end unknown.

Remarks. Without the abdominal part it is impossible to identify this specimen. It is unknown if Cossura sp. A has acicular chaetae on abdomen. It differs from most Cossura species with branchial filament arising from chaetiger 3 by its bigger size and its number of thoracic chaetigers (at least 28). Description of C. sima Fauchald, 1972 corresponds by the body width and number of thoracic chaetigers as well as by round shape of the anterior border of the prostomium, but in Cossura sp. A prostomium is longer and body rapidly expands in width beginning from the posterior prostomial ring, whereas in C. sima body width enlarges gradually; besides C. sima has dark pigment spots at the base of each parapodium and Cossura sp. A has uniform yellow body.

ACKNOWLEDGMENTS. This study was supported by Australian Museum Geddes Visiting Collection Fellowships, 2012 –2013, Russian Scientific Foundation, grant no. 14­50­00029, and a grant from the Russian Foundation of Basic Research no. 15-04-05875. All the research and collections staff at the Australian Museum were welcoming and very helpful. I am grateful to Stephen Keable for his great help with collections and databases, Sue Lindsay for assistance with SEM and light microscopy, Elena Kupriyanova, Pat Hitchings, and Anna Murray for their hospitality during my stay in Sydney. I am thankful to Geoff Read for sending specimens from New Zealand, and Linda Ward and Sergio Salazar­Vallejo for their help with literature. I express my sincere gratitude to Guy Bachelet and Óscar Díaz­Díaz for the critical reviews of manuscript which have significantly improved it.

Figures

Figure 17. Cossura sp. A. W.23618, stereomicroscope; B, D, methylen blue staining. (A) dorsal general view; (B) lateral general view; (C) anterior end, dorsal view; (D) anterior end, lateral view. Scale bars: A–D = 500 μm.