Cyclochlamys bacachorda, Dijkstra & Maestrati, 2015

Dijkstra, H. H. & Maestrati, P., 2015, Pectinoidea (Bivalvia: Propeamussiidae and Cyclochlamydidae) from the southwestern Indian Ocean, African Invertebrates 56 (3), pp. 585-585 : 622-623

Cyclochlamys bacachorda sp. n.

Fig. 8A–F

Etymology: From the Latin baca (f.) (pearl), chorda (f.) (string), after commarginal lirae with closely arranged small tubercles on left valve.

Description: Shell up to 3 mm in height, fragile, subcircular to circular, somewhat wider than high, stronglY inequivalve, almost equilateral, left valve more inflated than right valve, umbonal angle 105°, colourless and transparent.Auricles of similar size and almost contiuous with shell disc. Prodissoconch 270 µm long. Left valve smooth or sculptured with fine commarginal ridges in earlY growth stage (up to 2 mm maximum), coarse and prominent commarginal lirae or lamellae with close-set tubercles on intersections near ventral margin (3–5 per mm), closelY spaced fine radial threads (c. 10 per mm) multiply by intercalation. Auricles with close-set commarginal lirae or lamellae (5–8). Right valve with outer laYer of commarginallY elongate, hexagonal prisms, and broad, flexable ventral apron. Anterior auricle demarcated with shell disc, throughout commarginally sculptured, posterior continuous with shell disc and smooth.

Dimensions (holotype): height 3.0 mm, width 3.4 mm, convexity 0.7 mm.

Type material: Holotype, pr ( NMSA E55 /T4029). Type locality: SOUTH AFRICA: Off Nthlonyane River (32°17.2'S 29°04.9'E), - 220–230 m, live, branching sponges, gorgonians, NMDP stn P2, dredged RV Meiring Naudé, 17.vii.1982.

Paratypes: SOUTH AFRICA: KwaZulu­Natal: Off Durban (29°51.9'S 31°09.6'E), - 80–90 m, grey sandy mud, NMDP stn XX110, dredged RV Meiring Naudé, 09.vii.1986 ( NMSA D4904 , 1 lv); Off Umlaas

Canal (29°58.5'S 31°00.8'E), - 75 m, dead, muddy sand, NMDP stn XX77, dredged RV Meiring Naudé, 10.vii.1985 ( NMSA D4899 , 1 rv). Transkei: Off Mtamvuna River (31°08.9'S 30°15.7'E), - 111 m, dead, sponge, NMDP stn A14, dredged RV Meiring Naudé, 18.viii.1981 ( NMSA E14 , 1 lv); Off Port Grosvenor (31°25.6'S 29°58.0'E), - 100–110 m, dead, pebbles, some sand, NMDP stn D6, dredged RV Meiring Naudé, 13.viii.1981 ( NMSA A81 , 1 lv); Off Whale Rock (32°01.3'S 29°19.3'E), - 150–200 m, dead, sponge rubble, NMDP stn M8, dredged RV Meiring Naudé, 20.vii.1982 ( NMSA E65 , 5 lv, 14 rv); Off Nthlonyane River (32°17.2'S 29°04.9'E), - 220–230 m, live, branching sponges, gorgonians, TL - NMDP stn P2, dredged RV Meiring Naudé, 17.vii.1982 ( NMSA P0325 /T4030, 1 pr, 1 rv); Off Qolora River (32°41.4'S 28°30.0'E), - 80 m, dead, coarse sand, NMDP stn Y5, dredged RV Meiring Naudé, 13.vi.1983 ( NMSA E114 ); Off Qolora River (32°46.1'S 28°35.0'E), - 114 m, live, sponge rubble, NMDP stn Y8, dredged RV Meiring Naudé, 13.vi.1983 ( NMSA E41 , 2 pr, 1 lv, 1 rv) .

Distribution and habitat: South Africa, from off KwaZulu-Natal southwards to Transkei (29°S – 32°S). Living upper bathyally amongst sponges and gorgonians at a maximum depth range of - 114–230 m, minimum depth range - 114–220 m, shells at - 75– 230 m. Remarks:A somewhat resembling species by sculpture of the left valve is Cyclochlamys aupouria (Powell, 1937) , recorded from northern New Zealand. However, C. bacachorda differs from C. aupouria by having a coarser texture on the left valve of commarginal lirae or lamellae and wider spaced interstitial radial riblets ( C. bacachorda c. 10 per mm, C. aupouria c. 20 per mm), and by having a smooth or weakly sculptured shell disc in early ontogeny ( C. aupouria with commarginal lamellae and radial threads immediately commencing after larval stage). The prodissoconch of Cyclochlamys austrina Dijkstra & Marshall, 2008 , a species known from southern New Zealand, resembles that of C. bacachorda by having somewhat similar diverged anastomosing threads.

Figures

Fig. 8. Cyclochlamys bacachorda sp. n., holotype: South Africa, off Nthlonyane River, (A) external view of the left valve, H = 3 mm, scale bar = 1 mm; (B) external view of the right valve, H =, scale bar = 1 mm; (D) prodissoconch of the left valve, H = 3 mm, scale bar = 0.1 mm; (E) details of the left valve, H = 3 mm, scale bar = 0.1 mm; (F) details of the right valve, H = 3 mm, scale bar = 0.1 mm (NMSA E55/T4029); paratype, (C) external view of the right valve, H = 2.2 mm, scale bar = 0.5 mm (NMSA P0325/T4030). (G–H) Similipecten eous (Melvill in Melvill & Standen, 1907): campaign Mainbaza, stn CP3132, (H) external view of a left valve, H = 2.6 mm, scale bar = 1 mm; (H) details of a left valve, H = 2.6 mm, scale bar = 0.1 mm (MNHN).