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 : 16

Cossura sp. cf. longocirrata

Webster & Benedict, 1887

Figs 12 , 13

Cossura longocirrata Webster & Benedict, 1887: 743 , pl. 8, figs 105–107. — Fournier & Petersen, 1991: 65, figs 1–2.

Type locality. Eastport , Maine .

Material examined. New South Wales. 1 complete specimen, Pittwale (33°35'49"S 151°18'51"E), Ceridan Fraser’s Honour project, depth 15.8 m, sandy mud, coll. P.A. Hutchings, K.B. Attwood, C. Fraser, RV Baragula, NSW 2740, 02 Dec. 2004 , W.42959; 2 specimens, Pittwale (33°35'49"S 151°18'51"E), Ceridan Fraser’s Honour project, depth 15.8 m, sandy mud, coll. P.A. Hutchings, K.B. Attwood, C. Fraser, RV Baragula, NSW 2740, 02 Dec. 2004 , W.42960; 1 specimen, Pittwater (33°36'02"S 151°18'46"E), 25 Aug. 1994 , depth 16.1 m, mud, FAC2 05 Pit 2/2 B Australian Museum Party, W. 23619 ; 1 specimen, Hawkesbury River, near Hungry Beach (33°35'S 151°17'E), 27-V-83 1-1-1, depth 4 m, coll. A. R. Jones, A. Murray, Smith­McIntyre grab, sandy mud, W.43367 ; 1 specimen, Botany Bay , 200–500 m west of runway extension (33°57'49"S 151°10'26"E), F.A.C. Study, G6­2­4, NSW­772, April 1992 , depth 7 m, W.43325; 3 specimens, Hawkesbury River, near Hungry Beach (33°35'S 151°17'E), 04 Feb. 1983 , Hawkesbury River Survey, depth 4 m, Smith­McIntyre grab, sandy mud, coll. A. R. Jones, A. Murray, W. 43253 ; 1 specimen, Hawkesbury River, between Juno Head and Hungry Beach, mid­stream (33°34'S 151°16'E), Hawkesbury River Survey, depth 10 m, 06 Nov. 1981 , Smith-McIntyre grab, muddy sand, coll. A. R. Jones, A. Murray , W.43254 ; 24 specimens, Hawkesbury, Brooklyn Boat Channel (33°33'S 151°14'E), River Brooklin dredging, H. R. S. Polychaetes, 21 Aug. 1980 , coll. A. R. Jones et al., W.196734 .

Description. Complete specimen (W.42959) has 46 chaetigers, body length 5.6 mm, body width 200 μm.Another incomplete specimen is 300 μm in width, 2.3 mm in length having 27 chaetigers. 13–18 (in rare case 22–23) thoracic chaetigers without clear border between regions ( Figs 12A,B , 13A ). In thoracic region chaetae emerge from the anterior margin of segments, body flattened dorsoventrally, segments short. Methylen blue staining revealed dark, probably glandular cells on lateral and dorsal parts of segments, but segments are not inflated ( Figs 12H , 13A ). In abdominal region segments longer, body cylindrical, chaetae thinner and less numerous ( Figs 12A,B , 13A ).

Prostomium conical, not flattened, with pointed tip, without eyes, nuchal organs not seen ( Figs 12I , 13B,C,F ). Prostomial furrow well defined in contracted specimens, in well-relaxed specimens absent. Posterior prostomial ring shorter than peristomium. Lateral margins of both prostomial parts usually convex, less straight ( Figs 12B,F , 13I ). Branchial filament arising from posterior part of chaetiger 2; in contracted specimens looking as attached to border between chaetigers 2 and 3 ( Figs 12G,H , 13B,C ).

Chaetiger 1 with uniramous parapodia, all the next segments bear biramous ones. All chaetae hirsute capillaries; arranged in two rows. Thicker chaetae located in anterior row, thinner ones in posterior. First chaetiger bearing 4–7 chaetae, next up to 9 in notopodia and up to 10 in neuropodia. 3 thick anterior neuropodial chaetae thicker than 3 thick anterior notopopodial chaetae ( Figs 12E , 13H,I ). In posterior thoracic and abdominal chaetigers all chaetae becoming thinner, less numerous and less hirsute, 4–5 chaetae per ramus ( Figs 12G , 13J ).

Oocytes observed in body cavity in specimens from Pittwale (W.42960) and Hawkesbury River (W.43367).

Pygidium with three long anal cirri, without intercirral processes ( Figs 12F , 13D ). Cirri easily lost, in most specimens only one or two cirri present. In one specimen (W.42960) pygidium was regenerating ( Fig. 13B,C ).

Remarks. This species closely resembled C. longocirrata Webster & Benedict, 1887 , having a conical prostomium, branchial filament inserted to chaetiger 2, no intercirral anal processes, absence of heavy acicular thoracic chaetae. Australian worms differ by generally less number of thoracic chaetigers (13–18, rarely up to 22, instead of 16–21 in C. longocirrata ). But it is not clear if they really belong to a separate species or represent an example of intraspecific variability. Detailed redescription of numerous specimens from different localities including type material of C. longocirrata was done by Fournier & Petersen (1991). They concluded it is a cold-temperate arctic-boreal species; it has usually been collected from below the halocline at a salinity of 30 or higher and a year-round bottom temperature below 5°C; it is doubtful whether C. longocirrata occurs anywhere in the Pacific Ocean. The most probably Australian worms described here represent a separate species but we did not find morphological characters allowing to erect a new species. An analysis using molecular methods is required to solve this problem. Furthermore, in our material was also present a similar species C. sp. cf. pygodactylata , that differs mostly by the presence of intercirral anal processes, but most specimens are incomplete, so there is a possibility that there is a mixture of two species in material referred to Cossura sp. cf. longocirrata .

Figures

Figure 12. Cossura cf. longocirrata Webster & Benedict, 1887. Light microscopy. A–F, compound microscope, G–I, stereomicroscope; G, H, methylen blue staining. (A) W.43325, general dorsal view; (B) W.42960, complete specimen with regenerating pygidium; anterior part dorsally, posterior ventrally; (C) same specimen, pygidium; (D) W.23619, lateral view; (E) same specimen, parapodia of chaetigers 3–7; (F) same specimen as in (D), pygidium; (G) W.43367, general lateral view; (H) same specimen as in (G), anterior end laterally; (I) same specimen, anterior end dorsally. Scale bars: A, B = 500 μm, C, E, F = 100 μm, D, H, I = 200 μm, G = 300 μm.

Figure 13. Cossura cf. longocirrata Webster & Benedict, 1887. SEM. A, B (W.196734), C–J (W.42959). (A) dorsal general view; (B) anterior end, dorsal view; (C) anterior end, lateral view; (D) pygidium, ventral view; (E) anterior region, lateral view; (F) anterior end, dorsal view; (G) posterior region, dorsolateral view; (H) notopodia of chaetigers 5–6; (I) neuropodia of chaetigers 5–6; (J) parapodia of chaetiger 22. Scale bars: A = 300 μm, B, E, G = 100 μm, C, D, F = 20 μm, H–J = 10 μm.