Pecten dijkstrai Duncan & Wilson, 2012

Dijkstra, Henk H. & Beu, Alan G., 2018, Living Scallops of Australia and Adjacent Waters (Mollusca: Bivalvia: Pectinoidea: Propeamussiidae, Cyclochlamydidae and Pectinidae), Records of the Australian Museum (Rec. Aust. Mus.) 70 (2), pp. 113-330 : 225-227

Pecten dijkstrai Duncan & Wilson, 2012

Figs 56, 57C–E,H, 58E–I

Pecten cf. excavatus Anton, 1839 [sic].–Taylor & Glover, 2004: 262.

Pecten sp. nov. –Duncan & Wilson, 2007: 1306.

Pecten dijkstrai Duncan & Wilson, 2012: 21–26 , figs 1–3.

Type material. Holotype (pr) Western Australia, off Gnaraloo, 23°52'S 113°29'E, 40–42 m, in areas of coral sand around low-profile, sponge-encrusted limestone reef (H 39.40 mm, L 43.80 mm; D 16.40 mm) AM C.462684, and 30 paratypes (pr & v) as follows: Western Australia, off Gnaraloo Station, 130 km N of Carnarvon, 23°52'S 113°29'E, dead, 40–42 m, on areas of coral sand around low-profile, sponge-encrusted limestone reef (holotype and 2 paratypes (pr), AM C.462684, GW, PD); Exmouth, N of North-West Cape, approx. 21°32'S 114°24'E, dead, 35–40 m, on coral sand adjacent to low-profile limestone reef (2 paratypes (pr), GW, PD); North West Shelf, 52 n. ml NNE of Port Hedland, 19°30.9'– 19°28.2'S 118°49.2'– 118°55.4'E, dead, 36–37 m, sand (2 paratypes (v), C.149192; paratype (v), AM C.149173); North West Shelf , 77 n. ml NNE of Port Hedland, 19°05'– 19°04.9'S 118°58'– 118°58.2'E, dead, 82 m, sand & gravel (paratype (v), C.149343); North West Shelf , 78 n. ml NNE of Port Hedland, 19°04.4'– 19°04.2'S 119°04.4'– 119°00.7'E, dead, 82 m, sand (2 paratypes (v), C.149327); North West Shelf , 80 n. ml NNE of Port Hedland, 19°03.6'– 19°03.4'S 119°03.4'– 119°03.5'E, dead, 82 m, sand (20 paratypes (v) [juv-adult], C.146784).

Additional material examined. WESTERN AUSTRALIA: West of Point Quobba, 30 ml N of Carnarvon, approx. 24°27'S 113°40' E, alive, 35–40 m (1 pr, HM); Exmouth, north of N Murrion Island, 21°39'S 114°22' E, alive, 30 m, sand & gravel (1 pr, HM); North West Shelf , 52 n. ml NNE of Port Hedland,19°30.9'– 19°28.2' S 118°49.2'– 118°55.4' E,dead, 36–37 m, sand,dead (2 v, C.149192;1 v,C.149173); NNE of Dampier Archipelago, 19°23'S 117°21' – 117°23' E, alive, 101–102 m (1 pr, WAM S30715 ); North West Shelf , 19°05'S 118°50'E, alive, c. 80–100 m, muddy sand (1 pr, ZMA Moll.409005);off Broome, 17°58'S 122°14'E,alive, 12–18 m, coarse rubble(2 pr, HM; 1 pr, ZMA Moll.409006);and two addional illustrated HM specimens listed below .

Description. Shell subcircular, thin, up to c. 55 mm in length, broader than high, subequilateral, strongly inequivalve. Left valve richly pigmented with brown streaks and creamy-white dots on cream or pinkish background; right valve paler to almost whitish.

Left valve strongly concave, with 12–13 low, almost flat-topped radial plicae, with 1-3 rudimentary plicae near anterior and posterior margins; interstices each broader than one plica. Delicate, closely spaced commarginal lamellae on entire disc, almost smooth on central part, more prominent near margins. Anterior auricle slightly larger than posterior one, anterior edge rather concave; both auricles covered with

Figure 58. A–D, Pecten fumatus Reeve , 2 pairs; (A, B) AM C.080194, meridionalis form, 2.5 miles N of Beaching Bay, Maria Island, TAS, 82.5–91.5 m; rv exterior (A), lv exterior (B); (C, D) AM C.102334, preissiana form, prawn trawl, Shark Bay, WA; lv exterior (C); rv exterior (D). E–I, Pecten dijkstrai Duncan & Wilson , 2 pairs, both HM; (E, H, I) specimen in Fig. 57C–E, H; rv exterior (E), lv exterior (H), rv exterior anterior view (I); (F, G) Murion Island, 8 km NE of North West Cape, Exmouth, WA, 30–38 m; lv exterior (F), rv exterior (G). Scale bars represent 30 mm (A–D), 20 mm (E–I).

fine, close-set, unevenly developed, prominent commarginal lamellae; with or without 1-3 weak radial ridges near dorsal margin. Dorsal margin straight. Interior surface with paired angular internal rib carinae; adductor muscle scar welldefined; resilifer triangular; prominent resilial, intermediate and dorsal teeth developed on both sides of resilium.

Right valve strongly inflated, with 12–14 broad, low radial plicae with rounded crests, some specimens with a narrow radial groove on plical crests near ventral margin, plus 1-3 rudimentary plicae near anterior and posterior margins; interstices each much narrower than one plica. Delicate, close-set commarginal lamellae present near ventral margin; central part of disc smooth.Auricles of some specimens with c. 5 weak radial riblets; most specimens with fine, closely spaced commarginal lamellae (less well-developed than on left valve). Byssal notch shallow, functional ctenolium absent in adult stage. Dorsal margin straight; teeth and sockets prominent, corresponding to those in left valve.

Dimensions. Illustrated specimens: WA, Exmouth, Murion I., 8 km NE of North West Cape, 30–38 m (HM): rv, H 49.0, L

55.1, D (single valve) 23.3 mm; lv, H 41.5, L 54.1, D (single valve) 10.4 mm; WA, Exmouth, 7–8 km N of tip of North West Cape, 32–35 m (HM): rv, H 50.6, L 52.8, D (single valve) 24.6 mm; lv, H 41.6, L 51.4, D (single valve) 11.3 mm.

Habitat. Living in the sublittoral zone to the mid-continental shelf on soft sediment of sandy patches within flat reef areas.

Distribution. Continental shelf of Western Australia, from Carnarvon to northwest of Port Hedland. Possibly also southern Indonesia. Present specimens alive at 18–101 m (minimum depth range).

Remarks. Pecten dijkstrai is most nearly similar to Pecten excavatus Anton, 1838 , known from southern Japan to Indonesia. Pecten dijkstrai is less solid and somewhat wider than P. excavatus . The left valve of P. dijkstrai is also more deeply concave and the radial plicae are weaker and less angular than in P. excavatus . Pecten dijkstrai is also paler in colour than P. excavatus . Other characters are identical.

Pecten dijkstrai differs strongly from P. fumatus in having a much more deeply concave left valve; it is almost flat in P. fumatus . The right valve of P. dijkstrai is also more strongly convex than that of P. fumatus . Pecten dijkstrai is also thinner (less solid) and smaller in size (up to c. 55 mm in length; P. fumatus up to c. 170 mm in length) and less nearly circular than P. fumatus . Pecten fumatus also has more strongly developed radial plicae than P. dijkstrai . For comparison with Pecten afribenedictus Kilburn & Dijkstra, 1995 from South Africa and Pecten erythraeensis G. B. Sowerby II, 1842 from the Red Sea see Kilburn & Dijkstra (1995).