Hemipecten forbesianus A. Adams & Reeve, 1849

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 : 236-237

Hemipecten forbesianus A. Adams & Reeve, 1849

Figs 64, 65D–E, 67A,C

Venilia concentrica A. Adams & Reeve , in Anonymous, 1848: 776 ( Petit, 2007: 99–101) (nomen oblitum).

Hemipecten forbesianus A.Adams & Reeve, 1849: 133 , pl. 1, fig. 2; Reeve, 1849: sp. 1, pl. 1, figs 1a–c, 2a–d; A. Adams & Reeve, 1850: 72, pl. 20, figs 1a–c, 2a–d; Pelseneer, 1911: 16, 31, pl. 12, fig. 13 [anatomy]; Kuroda, 1931: 82, figs 96–96a; Hertlein, 1969: N354, figs C.76.5a–b; Waller, 1972a: 256; Higo, 1973: 323; Habe, 1977: 88; Yonge, 1981: 29, figs 2e–5; Koyama et al., 1981: 69; Dance, 1990: 78, pl. 27, fig. 580; Dijkstra, 1990a: 5, pl. 2, figs 11–12; 1991: 24, fig.; Dijkstra et al., 1990: 3, fig.; Dijkstra, (1983–1994) 1991: 18, figs; Lamprell & Whitehead, 1992: [18], pl. 7, fig. 36; Higo & Goto, 1993: 577; Bernard et al., 1993: 51; Goto & Poppe, 1996: 909; Dijkstra & Marshall, 1997: 89, pl. 7, figs 1–6; Kilias, 1997: 137; Slack-Smith, 1998: 277, fig. 6.18E –F; Higo et al., 1999: 447; Wells, Slack-Smith & Bryce, 2000: 42; Higo, Callomon & Goto, 2001: 157, fig. B490 (lectotype); Slack-Smith & Bryce, 2004: 237; Taylor & Glover, 2004: 262; Dufour, Steiner & Beninger, 2006: 35; Raines & Poppe, 2006: 68, 71, upper figs; pl. 4, fig. 10; Petit, 2007: 99–101; Beninger & Decottignies, 2008: 137–141, figs 1A–H, 2A–F [anatomy]; Huber, 2010: 204; Dijkstra, 2013: 61, pl. 16, figs 2a–d (nomen protectum).

Semipecten forbesianus (A. Adams & Reeve) .–Melvill & Standen, 1907: 808.

Pecten difformis Odhner, 1917: 15 , pl. 1, figs 4–5. Cyclopecten (Hemipecten) forbesianus (A. Adams &

Reeve).– Rombouts, 1991: 79.

Type data. Hemipecten forbesianus A. Adams & Reeve : lectotype (pr) designated by Dijkstra & Marshall (1997: 89) NHMUK 1874.12.11.376, figured in Adams & Reeve (1849: pl. 1, fig. 2; 1850: pl. 20, figs 2a–d) ; paralectotype (pr) (Adams & Reeve, 1850: pl. 20, figs 1a–c) not in type lot, not traced. Type locality: Philippine Islands , Sulu Sea , c. 26 m.

Pecten difformis Odhner : syntypes (6 pr) Swedish Museum of Natural History, Stockholm, SMNH1555. Type locality: Western Australia, off Cape Jaubert , Pearl Bank [33 km offshore W of Cape Jaubert, 18°57'S 121°13'E].

Additional material examined. — AUSTRALIA: QUEENSLAND: Torres Strait ,alive (1 pr,C.303801); GBR, Lady Elliot Island, S end, 24°06'54"S 152°42'48"E, reef front slope, alive, 15 m, on Turbinaria (1 pr, WAM S41991 ; growth series, WAM S41992) . WESTERN AUSTRALIA: Esperance, Cull Island , 31°19'S 133°07'E,alive, 2–10 m (1 pr, WAM S14229 ) ; Geographe Bay , NE of Dunsborough, 33°37'S 115°18' E, alive (1 pr, WAM S41993 ) ; Geographe Bay , E of Dunsborough, 33°37'S 115°18'E,alive, 20 m (5 pr, WAM S14228 ) ; Dunsborough,off Castle Rock , 33°37'S 115°18'E, alive, 18 m (6 pr, WAM S41994 ) ; Abrolhos Islands , 28°48.5'S 114°01.5'E,dead, 40 m (1 v, WAM S41995) ; Abrolhos Islands , Beacon Island , 28°28'S 113°47'E, intertidal,reef flat, alive (1 pr, WAM S13339 ) ; Montebello Islands , Hermite Island , 20°28.06' S 115°32.42' E, alive, 6 m (1 pr, WAM S41996 ) ; Kimberley, Dampierland, Beagle Bay , “garden bottom”, 16°52' S 122°32'E, alive, 9 m (1 pr, WAM S41990) ; Kimberley, Albert Reef , 14°15'S 125°09' E, alive (1 pr, WAM S41997 ) ; Scott Reef, North Reef , approx. 14°0'S 121°45'E, east lagoon, sand flat, alive (1 pr, WAM S14231 ) . — REUNION: Boucan Canot , dead, 67 m (1 v, ZMA Moll. 142262) .— THAILAND: Phuket, S of Ko Ha Yai , alive, 24–30 m (1 pr, ZMA Moll. 145609) . — INDONESIA: Moluccas, Damar Island , 0°59' S 128°22'E, alive, 45 m (1 pr, ZMA Moll. 011396) .— SOLOMON ISLANDS : W side Malaupaina Island , 161°58'E 10°14.5'S, alive, 24–30 m (2 pr, WAM 12555; 1 pr, WAM 12543). CORAL SEA: Capel Bank, 25°20'S 159°44' E, alive, 56 m (1 pr, ZMA Moll. 143847) .— NEW CALEDONIA: Prony Bay, Ouen Islet , 22°32'S 166°38'E, alive, 23 m (1 pr, ZMA Moll. 142264) .

Description. Shell up to c. 40 mm high, most specimens smaller, to 20 mm; semi-translucent or opaque, milky white or cream to reddish brown, fragile, flattened; left valve slightly convex, right valve flat; highly irregular in shape (almost circular to obliquely oblong), inequivalve, inequilateral; auricles unequal in size and shape.

Both valves with very delicate antimarginal scratches ( Camptonectes -like microsculpture) throughout, macrosculpture lacking. Anterior auricle of right valve somewhat declined, separated from disc by suture, bearing weak radial riblets; other auricles not differentiated from disc. Byssal notch narrow, extremely deep, curving towards umbo, byssal fasciole small; ctenolium present throughout ontogeny, with 8–12 well-developed teeth; outer ligament rather broad, stationary; resilium narrow.

Dimensions. Illustrated specimen: QLD, Torres Strait (AM C.303801): rv: H 20.5, L 23.3 mm; lv: H 21.8, L 25.7 mm; D 4.4 mm.

Habitat. Living byssally attached to the scleractinian coral Turbinaria mesenterina (Dana) ( Yonge, 1981: 29) ; in Western Australia, forming large lettuce leaf-like formations amongst rubble and weed on sand in the intertidal to sublittoral zones. Usually found in groups of 5– 20 specimens, covered with epiphytes on the left valve .

Distribution. Tropical Indo-West Pacific, from southern Japan southwards to Australia, westwards into the Indian Ocean to Réunion, and eastwards into the Pacific to New Caledonia (Raines & Poppe, 2006: 70); Philippines, 4–30 m (Dijkstra, 2013: 61); Norfolk Island, 6–28 m (Dijkstra & Marshall, 1997: 89). Now also from the Solomons (24–30 m). Maximum depth range of live-taken specimens is from the intertidal zone to 67 m (Dijkstra & Marshall, 1997: 89). Present material from Australia living from the intertidal zone to 20 m.

Remarks. The present specimens are very variable in shape (circular to oblong and oblique), probably caused by their constricted living position on the scleractinian coral Turbinaria ( Yonge, 1981: 29) . The shell characters of the immature type specimens of Pecten difformis from Western Australia are identical to those of Hemipecten forbesianus at the same size. For descriptions of soft parts of this species see Yonge (1981) and, for the gills, Beninger & Decottignies (2008).

Petit (2007: 99–101) pointed out that the name Venilia concentrica was proposed for this species accidentally, in an anonymous report, with a recognisable description (“the lower valve having a remarkable lateral incison on the left side, after the manner of Pedum , whilst the hinge partakes of the structure of Pecten and Avicula ; both valves are, moreover, of the same fragile tenuity as the Placuna placenta ”) but that Venilia is a junior homonym. The name Hemipecten forbesianus was then proposed for it first by Adams & Reeve (1849: 133, pl. 1, fig. 2; 25 Apr 1849), later by Reeve (1849: Hemipecten monograph, sole species; text dated Sept 1849), and only in 1850 byAdams & Reeve (1850: 72, pl. 20, figs 1a–c, 2a–d; 31 Aug 1850) in the zoology of the “ Samarang ” voyage. In the chresonomy above we list the more than 25 usages of the name H. forbesianus (as the presumed valid name for this species by at least 10 authors during the last 50 years) that are required to make this name a nomen protectum under ICZN Article 23.9.1, and we declare Venilia concentrica a nomen oblitum.