Cossura hutchingsae, 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 : 10-11

Cossura hutchingsae n. sp.

Figs 7 , 8

Type locality. Australia, New South Wales, Hawkesbury River.

Type material. Holotype anterior fragment with 18 chaetigers, all thoracic, 3 mm long, 0.64 mm wide, New South Wales, Hawkesbury River, 200 m south of eastern end of Spectacle Island , 8­V­84 3­3­ 3 W. 43372.

Paratypes, 9 specimens, Victoria, mouth of Yarra River, Hobsons Bay, Port Phillip Bay (37°50'29"S 144°53'52"E), 23 Jun. 1975, coll. Marine Studies Group, W. 16338; 1 specimen, New South Wales, Hawkesbury River, 200 m south-east of Croppy Point (33°33'S 151°17'E), 21-VIII-84 2­3­3, W.42865 .

Additional material examined. New South Wales. 1 specimen, Hawkesbury River, between Juno Head and Hungry Beach (33°34'S 151°16'E), mid-stream, 07 Aug. 1981, 1-3-2, depth 10 m, coll.A. R. Jones,A. Murray, W. 43417 ; 1 specimen, Hawkesbury River, 200 m south of eastern end of Spectacle Island (33°32'30"S 151°13'30"E), 3-3-2, 05 Aug. 1984, depth 5 m, Smith-McIntyre grab, sandy mud, coll. A. R. Jones, A. Murray, W. 43369 ; 1 specimen, 3242 Bega River, Tathra 2008, west of Hancock Bridge (36°41'54"S 149°58'15" E), depth 5.9 m, 3 April 2008, coll. K.B. Attwood, S.J. Keable, A. Murray , R. T. Springthorpe, RV Baragula, van Veen grab, sandy mud, W.43346 ; 1 specimen, west of La Perouse, Botany Bay (33°59'24"S 151°12'48"E), 10 Mar. 1977, depth 13 m, coll. State Pollution Control Commission , st.99, W.13652; 1 specimen, Botany Bay, west of La Perouse (33°59'18" S 151°12'38"E), depth 19.2 m, 02 Feb. 1977, col. State Pollution Control Commission , st.81, W.13653.— Queensland. 1 specimen, Calliope River, Gladstone (23°51'S 151°10'E), Dec. 1976, coll. P.Saenger , W.13224.

Diagnosis. Prostomium trapezium-shaped with wide round anterior margin. 17–21 thoracic chaetigers; border between body regions unclear. Branchial filament arising from border between chaetigers 2 and 3. Anterior margins of thoracic segmental borders dorsally drawn forward. Thoracic neuropodia with 2–3 very thick bent chaetae with long thread-like distal tips; other chaetae in thorax and abdomen capillary.

Description. All specimens incomplete, with 18–50 segments, 4–12 mm in length, 0.4–0.8 mm in width. Anterior region (thorax) with 17–21 chaetigers; border between regions unclear ( Figs 7A , 8A,B ). In specimen with gametes in body cavity they start from chaetiger 24. Thoracic chaetigers have glandular inflations on their lateral and dorsal sides, mid-dorsally dorsal groove located between them. Anterior margins of segmental borders dorsally drawn forward, to the base of branchial filament ( Figs 7B,E , 8A ). Segments becoming longer in the abdominal region.

Prostomium trapezium­shaped, flattened dorsoventrally, anterior margin from semi-circular to almost straight ( Figs 7B,E , 8C ). Posterior ring as long as peristomium; border with peristomium not always clear; prostomial furrow developed to various degrees; in some specimens additional furrows in prostomium and peristomium.

Branchial filament arising from border between chaetigers 2 and 3 ( Figs 7B,D–F , 8C,D ), in some cases may be impression of its attachment from anterior border of chaetiger 3. Nuchal organs not seen.

Chaetiger 1 with uniramous parapodia, all next segments bearing biramous parapodia. All chaetae hirsute capillaries with smooth shafts; arranged in two indistinct rows. Thicker chaetae are located in anterior row, thinner ones in posterior ( Fig. 7D,F,G ). First chaetiger bears four or five chaetae, in next segments notopodia bear 5 chaetae in anterior row and 4–5 in posterior, neuropodia bear 2–3 very thick (14–16.5 μm in thickness) bent chaetae with long thread­like distal tips in anterior row and 4–5 capillaries in posterior ( Figs 7F,G , 8E,F ). After chaetiger 10–13 these thick chaetae replaced with normal capillary chaetae. Chaetae in abdomen thinner and more numerous, 12–14 chaetae per ramus ( Fig. 8G ).

Gametes in body cavity were observed in one specimen from Victoria (W.16338) ( Fig. 7A ).

Posterior end unknown.

Etymology. This species has been named in honour of Pat Hutchings from Australian Museum, in recognition of her great contribution to the knowledge of polychaetes and Australian marine biota.

Remarks. Thickened chaetae in thoracic chaetigers are described also for Cossura heterochaeta , C. rostrata Fauchald, 1972 , and C. ginesi . Cossura ginesi differs by the shape of prostomium with anterior extension. Cossura heterochaeta and C. rostrata have a conical prostomium (round to obtuse in C. hutchingsae n.sp.), and there are two types of anterior thickened chaetae—with arista and without it—in C. heterochaeta , whereas in our worms they are uniform having aristas. Besides, C. hutchingsae n.sp. has more anterior segments (17–21 instead of 12–14 in C. heterochaeta ). The most characteristic features of this new species are the inflated pads in thorax and the segmental borders drawn forward dorsally, giving it a peculiar appearance.

Figures

Figure 7.Cossura hutchingsae n. sp. Stereo microscope,C–G stained with methylen blue.(A) paratype,W.16338, dorsolateral view, gametes in the middle region are seen; (B) W.43346, anterior end, dorsal view; (C) paratype, W.42865, dorsolateral view (arrow indicates border between regions; chaetae bundles shifted to the middle of segments);(D) W.13652, anterior end, lateral view; arrowhead indicates mouth opening; (E) holotype, W.43372, anterior end, dorsal view; (F) holotype, W.43372, anterior end, lateral view; (G) W.43369, chaetigers 3–13, lateral view. Scale bars: A, D = 600 μm, B, E, F, G = 200 μm, C = 1 mm.

Figure 8. Cossura hutchingsae n. sp. Paratype, W.42865, SEM. (A) general view from dorsal side; (B) general view from lateral side; (C) anterior end, dorsal view; (D) anterior end, lateral view; (E) notochaetae of chaetiger 3; (F) neurochetae of chaetiger 6; (G) parapodia of chaetiger 25. Scale bars: A, B = 1 mm, C, D = 200 μm, E, F = 20 μm, G = 100 μm.