Mesopeplum fenestratum (Hedley, 1901)

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 : 173-176

Mesopeplum fenestratum (Hedley, 1901)

Figs 28, 29C–E, 31C–D

Chlamys fenestrata Hedley, 1901: 730 , pl. 48, figs 17–19; Hedley, 1902: 307; Pritchard & Gatliff, 1904a: 265; Hedley, 1918a: M9; Iredale, 1924: 194.

Chlamys hedleyi Dautzenberg, 1902: 347 (unnecessary replacement name for Chlamys fenestrata Hedley, 1901 , not preoccupied by Pecten fenestratus Forbes, 1844 ). See also Dijkstra (1998b: 248, 251).

Mesopeplum caroli Iredale, 1929: 162 , pl. 38, figs 6–8; Allan, 1950: 281, pl. 37, fig. 4; Macpherson & Gabriel, 1962: 305, figs 346A–B; Iredale & McMichael, 1962: 11; Garrard, 1969: 11; Rombouts, 1991: 61, pl. 22, fig. 4; Waller, 1991: 30, pl. 3, figs 13, 17.

Mesopeplum triggi Cotton & Godfrey, 1938: 97 , fig. 83; Cotton, 1961: 101, fig. 87; Rombouts, 1991: 61, pl. 28, fig. 5.

Mesopeplum fenestratum (Hedley) .–Allan, 1950: 281; Iredale & McMichael, 1962: 11; Garrard, 1969: 5; Lamprell & Whitehead, 1992: [30], 173, pl. 13, fig. 78; Beu & Darragh, 2001: 171, figs 60F(?), 61A–I, 62A–H; Raines & Poppe, 2006: 84, 87, upper figs; pl. 23, figs 1–5; Huber, 2010: 212.

Semipallium (Mesopeplum) caroli (Iredale) .–Hertlein, 1969: N366, figs C.88.3a–b. Semipallium fenestratum (Hedley) .–Coleman, 1975: 280, fig. 770.

Decatopecten caroli (Iredale) .–Wells & Bryce, 1985: 160, fig. 585.

Mesopeplum convexum (Quoy & Gaimard) .–Lamprell & Whitehead,1992:[30], 171, pl.13, fig.79 (misidentification).

Type data. Chlamys fenestrata Hedley : holotype (lv) AM C.008971 (Fig. 29C). Type locality: Australia, New South Wales, Sydney Harbour, off Ball’s Head , 18 fathoms [33 m].

Mesopeplum caroli Iredale : holotype (pr) AM C.170894. Type locality: Australia, southern New South Wales, off Montague Island, 55–60 fathoms [101–110 m]. Despite being allovated a catalogue number, the holotype is not recognisable in the Australian Museum. The illustrated specimen, AM C.347523 (Figs 29D–E, 31C–D), from southern New South Wales, off Jervis Bay, 37–124 m, closely resembles Iredale’s (1929: pl. 38, figs 6–8) illustration of the holotype, and is here designated the neotype of Mesopeplum caroli Iredale, 1929 .

Figure 29. A, B, Pseudamussium challengeri (Smith) , pair, AM C.155798, E of Brush Island, NSW, 35°28'– 35°33'S 150°50'– 150°47'E, 604 m; lv exterior (A), rv exterior (B). C–E, Mesopeplum fenestratum (Hedley) ; (C) immature lv exterior, holotype of Chlamys fenestrata, AM C. 008971, lv, off Ball’s Head, Sydney Harbour, NSW, 18 fathoms [33 m]; (D, E) neotype of Mesopeplum caroli Iredale , pair, AM C.347523, off Jervis Bay, NSW, 35°05'S 150°45'E, 37–124 m; rv exterior (D), lv exterior (E). F–H, Anguipecten picturatus Dijkstra , pair, ZMA Moll.142043, Chesterfield Islands , Coral Sea, 19°12'S 158°50'E, 62 m; lv exterior (F), lv interior (G), rv exterior (H). I, J, Anguipecten simoneae Morrison & Whisson , paratype, pair, HM10773, near Mermaid Reef, Rowley Shoals, WA, 17°05'S 119°35'E, 100–150 m; lv exterior (I), rv exterior (J). Scale bars represent 10 mm (A–C, F–J), 20 mm (D, E).

Mesopeplum triggi Cotton & Godfrey : holotype (rv) SAM D13289, 3 paratypes (rv) SAM D15643. Type locality: Australia, SA, Great Australian Bight , 80 miles W of Eucla, 100 fathoms [183 m].

Comments on type data. Iredale’s (1929) assertion that Hedley’s species Chlamys fenestrata is based upon an adult specimen is incorrect. The holotype of Chlamys fenestrata is an immature specimen morphologically identical to adult specimens of Mesopeplum caroli .

Cotton & Godfrey (1938) introduced a species, Mesopeplum triggi , from the Great Australian Bight, which in their opinion is similar to the Miocene fossil species Pecten polymorphoides Zittel, 1865 (i.e., presumably intended for Mesopeplum minimum Beu & Darragh, 2001 ) and M. incertum ( Tenison Woods, 1865) , but which in our opinion is part of the variation of M. fenestratum . For comparison and discussion see Beu & Darragh (2001: 159; Beu et al., 2012: 34). For comparison with Mesopeplum convexum see below.

Additional material examined. — AUSTRALIA: QUEENSLAND: Capricorn Channel , 22°30'S 152°0'E, dead (2 pr, C.303792); ESE of Noosa Heads, 26°34'S 153°40'E,dead, 128 m (3 v,C.096125) ; off Caloundra , 26°47'S 153°35'E, dead, 128 m (1 v, C.375126) ; E of Moreton Bay , 26°55'S 153°33'E, dead, 115–176 m (8 v, C.375129) ; NE of Cape Moreton , 26°55.5'S 153°33.5'E, dead, 115–124 m (7 v, C.375127) ; NE of Cape Moreton light, 26°55.5'S 153°33.5'E, dead, 115–119 m (11 v, C.375128) ; E of Cape Moreton , 27°0' S 153°36'E, dead, 128 m (5 v, C.097580) ; off Moreton Bay , 27°27.37' S 153°39'E, dead, 77 m (2 v, C.133546) ; off Moreton Bay , 27°31'S 153°40'E,dead, 75–80 m (9 v,C.095216) . NEW SOUTH WALES: E of Tweed Heads , 28°11'– 28°14' S 153°50'E, dead, 146 m (8 v, C.347730) ; E of Tweed Heads , 28°12'– 28°19'S 153°50'E, dead, 152–155 m (1 v, C.116445) ; off Tweed Heads , 28°12'– 28°14'S 153°50'– 153°51' E, dead, 172 m (2 v, C.347731) ; off Danger Point , 28°13'– 28°18'S 153°50'E, dead, 132–135 m (5 v, C.117875) ; E of Tweeds Heads , 28°16'– 28°12'S 153°50'– 153°51'E, dead, 146 m (1 v, C.347729) ; off Tweed Heads , 28°17'S 153°44'E,dead, 73 m (14 v,C.117653) ; off Hastings Point , 28°20.4' S 153°47.1' E, dead, 82 m (1 v, C.096262) ; E of Tweed Heads , 28°21'– 28°24'S 153°48'– 153°49'E, dead, 165–174 m (1 v, C.347728) ; off Cape Byron , 28°43'– 28°39'S 153°51'– 153°50' E, dead, 128–139 m (2 v, C.116405) ; 18 km E of Ballina , 28°49.8'S 153°47.8' E, dead, 91 m (2 v,C.108688) ; N of Coffs Harbour , 29°40.3'S 153°30.4'E,dead, 71 m (1 v,C.347712) ; 14 km E of Coffs Harbour , 30°18.4' S 153°17.7'E, dead, 76 m (1 v,C.347726) ; off Coffs Harbour ,30°36'– 30°39' S 153°19'– 153°18'E, dead, 165 m (1 v,C.123477) ; off Manning River , 31°53'S 152°45' E, dead, 13.7–15.2 m (3 v, C.347722) ; S of Port Macquarie , 32°02'S 152°40' E, dead, 47 m (7 v, C.347725) ; NE of Port Stephens , 32°18'– 32°12'S 152°43' E, dead, 91 m (9 v, C.347709) ; off Port Stephens , 32°26'S 152°41' E, dead, 100 m (2 v, C.347708) ; Broughton Island , 4.8 km offshore, 32°38'S 152°25'E, alive, 82–92 m (many, C.119746) ; off Broughton Island , 32°38'S 152°25'E, dead, 91 m (4 v, C.130897) ; Port Stephens, 32°42'S 152°05'E, dead (8 v, C.012049;1 pr,C.097681);off Port Stephens , 32°42'S 152°15'E, dead, 35 m (2 v, C.097582) ; 8 ml [13 km] E of Port Stephens , 32°42'S 152°19'– 152°20' E, dead, 101 m (1 v, C.100801) ; Nelson Bay, Port Stephens , 32°43.3' S 152°08.7'E, dead, 15 m (2 v, C.008972) ; off Broken Bay , 32°52'S 152°32'E, dead, 145 m (1 v, C.347653) ; off Newcastle , 32°58.8'S 152°41.6' E, dead, 951–1150 m (3 v, C.155844) ; off Norah Head , 33°17'S 151°39'E, alive, 46–55 m (1 pr, C.047898) ; off Tuggerah Lake , 33°20'S 151°39.4'E, dead, 60 m (2 v, C.130938) ; off Norah Head , 33°20'S 151°56'E, dead, 73–91 m (3 v, C.347651) ; 9–12 km NE of Cape Three Points ,33°32.5' – 33°31.25'S 151°31.4'– 151°34.9'E, dead, 75–91 m (1 pr + 2 v + fragm.,C.013242) ; off Broken Bay , 33°34'S 151°30' E, dead, 82–137 m (2 v, C.070406; 3 v, C.347664) ; off Barrenjoey, Palm Beach , 33°35'S 151°35'E, dead, 110 m (2 pr, C.080113) ; off Sydney , 33°36'– 33°37' S 151°30'– 151°29'E, dead, 71–75 m (3 v, C.357996;3 v, C.357996) ; 22 ml E of Narrabeen, N of Sydney , 33°42' S 151°43'E, dead, 146 m (2 v, C.026070) ; off Broken Bay , 33°43'– 33°41'E 151°46' – 151°43' E, dead, 170 m (5 v, C.347660) ; off Broken Bay , 33°43' S 151°40'E, dead, 143 m (10 v, C.347604) ; SE of Broken Bay ,33°43' – 33°41'S 151°37' – 151°39'E,dead, 139–146 m (2 v,C.082484) ; off Collaroy , 33°44' S 151°28'E,alive, 110 m (1 pr,C.077358) ; SW of Cape Naturaliste , 33°44.5' S 114°26.1' E,dead, 183–238 m (1 v,C.157642) ; Sydney N, Collaroy , E of Long Reef,33°45'– 33°43'S 151°30'– 151°31'E,dead, 110–119 m (1 v, C.098764) ; off Sydney , 33°46'S 151°43'E, dead, 176 m (1 v, C.155808; 3 v, C.155828) ; 29 km off Manly & Sydney Heads,33°48'– 33°50'S 151°35'– 151°36' E,dead, 137 m (1 v,C.117114) ; Sydney , 5.4 km E of North Head, 33°49.5'S 151°21.6'E,dead, 64–66 m (1 v,C.347797) ; Sydney , 5.6 km E of North Head, 33°49.5'S 151°21.8'E, dead, 66 m (1 v, C.347798) ; E of Port Jackson , 33°49.8' S 151°34'E,dead, 157–161 m , 1 v, dead (1 v, C.347618;1 v,C.347620); off Sydney, 33°50'S 151°19'E,dead (1 v,C.347623);5 ml off Sydney , 33°50' S 151°24' E, dead, 137 m (1 v, C.075954) ; off Port Jackson , 33°50'S 151°30'E, dead, 126–150 m (1 v, C.124113; 2 v, C.124117) ; E of Port Jackson , 33°50.8'S 151°32'E, dead, 135 m (2 v, C.124444) ; Sydney, Port Jackson, off Balls Head , 33°51'S 151°11.5'E, dead, 33 m (holotype [v], C.029103) ; Sydney ,9 ml E of Coogee, 33°55.5'S 151°26.3' E, alive, 119 m (1 pr,C.347828) ; E of Coogee , 33°55.8'S 151°22.8' E,dead, 86–104 m (3 v,C.124125) ; Sydney, off Coogee , 33°56'S 151°17.3'E, dead, 60 m (2 v, C.347622) ; Sydney, off Coogee , 33°56'S 151°25'E, dead, 86 m (15 v, C.124256) ; 2.6 km E of Maroubra Beach, Sydney , 33°57.1'S 151°17.62'E, dead, 58 m (1 v, C.347801) ; Sydney , E of Malabar, 33°58'S 151°27'E, dead, 137 m (4 v, C.129072) ; off Sydney , 33°58'S 151°29'E, dead, 150 m (many v, C.129015) ; Sydney , 5.5 km E of Long Bay, 33°58.1'S 151°18.22'E, alive, 77 m (1 pr, C.347832) ; Sydney , E of Long Bay, 33°58.2'S 151°16.78'E, dead, 47 m (3 v, C.347802) ; Sydney, off Malabar , 33°58.17' S 151°17.17' E, dead, 67 m (1 v, C.347803) ; off Sydney , 33°59'S 151°17'– 151°20'E, dead, 42–97 m (1 v, C.347791) ; Sydney , 2.3 km E of Malabar, 33°59.45'S 151°16.81'E, dead, 66–73 m (4 v, C.145003; 1 v, C.347608; 2 v, C.347610) ; Sydney , 2.3 km E of Malabar, 33°59.45'S 151°16.27'E, dead, 64 m (1 v, C.347800) ; E of Botany Bay , 34°0'– 34°01' S 151°16'– 151°17'E, dead, 73 m (1 v, C.347592) ; 13.7 km E of Cape Solander , 34°00.37'S 151°20.8' E, dead, 130–138 m (1 v, C.347598) ; 2.5–4 ml [4–6.4 km] off Botany Heads , 34°00.5' S 151°17.5'E,alive, 60–102 m (many,C.048076) ; E of Botany Bay , 34°00.9' S 151°20.1' E, dead, 104–110 m (3 v,C.124442) ; off entrance to Botany Bay , 34°01'S 151°16'E, dead, 60 m (1 v, C.124121) ; off Botany Bay , 34°01'S 151°19.8' E, alive, 91–101 m (1 pr, C.132127) ; Sydney , 10 km E of Cape Solander, 34°01.7'S 151°19.67'E, dead, 122 m (12 v, C.103634) ; 7 km E of Malabar , 34°02.25' S 151°18.92'E, dead, 70–130 m (1 pr, C.103637; 1 pr, C.347606) ; Sydney, off Cronulla , 34°03' S 151°12'E, dead, 64 m (4 pr, C.300341) ; Sydney,off Cronulla , 34°03'S 151°12.5'E,dead, 70–80 m (17 v,C.347571) ; NE of Port Hacking , 34°03'S 151°14.5'E, dead, 73 m (1 v, C.124252) ; off Sydney , 34°03'– 33°52'S 151°37'– 151°22' E, dead, 79–295 m (many v, C.347645) ; E of Port Hacking , 34°03.7' S 151°14.1' E, dead, 132 m (1 v, C.124448) ; off Cronulla , 34°04'S 151°14'E, dead, 40–100 m (7 v, C.081389; 6 v, C.121009; many v,C.347558) ; Sydney, off Cronulla , 34°04'S 151°15.5'E, dead, 100 m (1 v, C.347563) ; off Port Hacking , 34°04.8'S 151°25.2'E, dead, 145 m (2 v, C.097581) ; Port Hacking, off Jibbon , 34°05'S 151°13'E, dead, 85 m (many v, C.347584; 60–100 m, dead, 10 v, C.347585; 2 v, C.347586; 4 v, C.347587; 4 v, C.347589) ; off Port Hacking , 34°05' S 151°15'E, dead, 64 m (1 v, C.124255) ; off Wattamolla , 34°05'S 151°14.5' E, alive, 82 m (3 pr + 2 v, C.086740) ; off Botany to Wattamolla , 34°05' S 151°14.5'E,alive, 64 m (1 pr,C.111393) ; E of Botany Bay , 34°06'S 151°28'E, dead, 135–165 m , 2 v, dead (2 v, C.124173; 3 v, C.124183); SE of Cronulla , 34°07'– 34°02'S 151°19'– 151°21'E, dead, 130–134 m (1 v, C.347564) ; E of Wattamolla , 34°08'S 151°23.9' E, dead, 143 m (5 v, C.347535) ; E of Cronulla , 34°09.03'S 151°16.21' E,dead, 126–132 m (1 v,C.347561) ; off Stanwell Park , 34°13.8' S 151°07.8'E,alive, 91 m (3 pr + 6 v,C.063423) ; off Botany Bay , 34°19'– 34°20'S 151°19'– 151°18'E, dead, 161 m (6 v, C.123371) ; 10.75 ml SE of Bulli Point , 34°20'S 150°55.8'E, dead, 128 m (1 v, C.347540) ; off Port Kembla , 34°20'S 151°18'E, dead, 161 m (1 v, C.347528) ; 16 ml E of Wollongong , 34°25'S 151°15'E, dead, 183 m (4 v, C.017976) ; off Wollongong, 34°26.13'S 151°05'E,dead (1 v,C.074707);5-8 ml off Port Kembla , 34°27.9'– 34°30.4' S 151°04.5'– 151°00.9'E, alive, 115–137 m (1 pr + 3 v, C.013202) ; off Shellharbour , 34°34' S 151°05'E,dead (2 v,C.347526); 4–4.8 km offshore in Shoalhaven Bight, 34°48.8'– 34°52.1' S 151°49.1'– 151°48.2'E, alive, 35–37 m (1 pr, C.013184) ; off Crookhaven , 34°55'S 150°54'E, alive, 55–64 m (2 v, C.089267; 1 pr + 1 v, C.119745) ; off Jervis Bay , 35°05'S 150°45'E,alive, 37–124 m (1 pr,C.347523) ; off Jervis Bay , 35°05'S 151°02.5'E,dead, 119 m (11 v,C.130896) ; off Wreck Bay , 35°11.8'S 150°38.2'E,alive, 27 m (3 pr, C.119744) ; off Ulladulla, 35°21'S 150°31.5' E,alive (3 pr + 2 v, C.130895); Ulladulla, 35°21.5'S 150°28.5' E, dead (1 v, C.073005); off Burrill Lake , S of Ulladulla, 35°22.5'S 150°26' E, alive (1 pr, C.132126); Broulee Beach, S of Batemans Bay , 35°51'S 150°10.5'E,dead (1 pr,C.347522); 11 km N of Montague Island, 36°08.8'S 150°13.1' E, alive, 90 m (16 v, C.097583) ; off Montague Island , 36°14.2'S 150°15'E, alive, 82–110 m (1 pr,C.130894) ; off Montague Island , 36°16.4'S 150°17'E, alive, 128 m (2 pr, C.347842) ; 10 ml N of Eden , 36°55'S 149°55'E, dead, 18–46 m (1 v, C.347525) ; Twofold Bay, Eden, 37°04'S 149°54.2'E, dead (1 v, C.347419); Twofold Bay , off Eden , 37°04.8'S 149°58.9' E,alive, 37–73 m (4 pr,C.130893) ; off Eden , 37°05'S 150°0'E, alive, 55–91 m (1 pr, C.130892; 1 pr, C.132125; 1 v, C.154255) ; off Green Cape , 37°16' S 150°13'E, alive, 91–128 m (2 pr, C.049895) ; S of Eden , 37°24' – 37°19'S 150°17'– 150°21' E,dead, 91–274 m (2 v,C.108311) ; 20 ml [32 km] SE of Twofold Bay , 37°26'S 150°15'E,dead, 149 m (2 v,C.346829) . VICTORIA: off Twofold Bay , 37°40.5'S 150°04' E, alive, 71 m (1 pr, C.347481) ; off Lakes Entrance , 38°03'S 148°03.5'E, dead, 36–46 m (1 v,C.375124) ; Bass Strait,off Cape Everard , 38°07'S 149°17'E,dead, 128–146 m (1 v,C.300342) ; Bass Strait,25 ml off Cape Everard , 38°22'S 149°13'E,dead, 132–146 m (1 v, C.375125) . SOUTH AUSTRALIA: off Beachport , dead, 274 m (2 v, SAM D19025) . WESTERNAUSTRALIA: GreatAustralian Bight ,50 ml SW of CapeAdieu, 32°42'S 131°27'E,dead, 79 m (5 v,C.375120) ; GreatAustralian Bight , 33°20'S 128°45'E, dead, 140–147 m (3 v, C.375123) ; Great Australian Bight , 33°05'– 33°20'S 128°40'– 128°45'E, dead, 75–147 m (3 v, C.375122) ; Great Australian Bight , E of Hood Point, 34°25'S 121°20'E, dead, 158 m (13 v, C.124176) ; S of Cape Leeuwin , 34°25'– 34°45'S 114°40'– 115°0'E, dead, 73–144 m (1 v, C.375119) ; WSW of Cape Leeuwin , 34°25'S 114°36.5'E, dead, 142–146 m (3 v, WAM) ; off Cape Leeuwin , 34°14'S 114°27'E, dead, 161–190 m (1 v, WAM) ; NW Cape Freycinet , 33°57.2'S 114°30'E,dead, 153–160 m (1 v, WAM) ; 33°40'S 114°28'E, dead, 137 m (12 v, WAM) ; NW of Bunbury , 33°0'S 114°37'E, dead, 219–221 m (1 v, WAM) ; NW of Bunbury , 32°57.5'S 114°48'E, dead, 122–139 m (11 v, WAM) ; W of Garden Island , 32°19'S 115°07' E, dead, 148–154 m (5 v, WAM) ; W of Rottnest Island , 32°0'S 115°15'E, alive, 146–150 m (9 v, WAM; 1 pr + 5 v, WAM626-74 ; 6 v, WAM) ; W of Rottnest Island , 32°0' S 115°16'E, dead, 137–143 m (2 v, WAM) ; W of Rottnest Island , dead, 146–183 m (3 v, WAM; 2 v, WAM; 1 pr + 3 v, WAM1103-81 ) ; WNW of Rottnest Island , dead, 174–175 m (4 v, WAM N4256 ) ; NW of Rottnest Island , dead, 146–163 m (6 v, WAM N4416 ; 13 v, WAM N4347 ) ; W of Garden Island , 32°15.7'S 115°06.7' E,dead, 176–182 m (1 v,C.375121) ; W of Rottnest Island , 31°59'S 115°14'E,dead, 182 m (1 v,C.165585) ; W of Guiderton ,31°30'– 31°34'S 114°56'– 115°06'E, dead, 146 m (1 v [flat form], C.165584; 2 pr + many v, WAM) ; W of Guilderton , 31°45'S 115°06'E, dead, 106–110 m (7 v, WAM) ; W of Lancelin , 31°0'S 114°52'E, dead, 183 m (1 v, WAM) ; W of Lancelin , 31°0'S 114°52.5'E, dead, 146–150 m (3 v, WAM) ; NW of Green Island , 30°37'S 114°44'E, dead, 139–146 m (1 pr + 5 v, WAM) ; 30°34'S 114°44'E, dead, 128 m (1 pr + 3 v, WAM) ; 30°30'S 114°32'E, dead, 168–177 m (1 v, WAM) ; 30°21'S 114°38'E,dead, 165 m (4 v, WAM) ; 40 km W of Jurien Bay , 30°15.9'– 30°16.5'S 114°38.6' – 114°38.7'E,dead, 137.2 m (1 pr + 7 v, WAM) ; NW of Jurien Bay , 29°59'S 114°25'E, dead, 146–152 m (2 pr + 9 v, WAM) ; W of Dongara , 29°49'S 114°24'E, dead, 128–132 m (3 v, WAM) ; SW of Dongara , 29°49'S 112°24'E, alive, 128–132 m (13 v, WAM; 2 pr, WAM) ; NW of Beagle Island , 29°43'S 114°20'E, dead, 183 m (3 v, WAM) ; WSW of Dongara , 29°31'S 114°11'E, dead, 221–227 m (1 v,

WAM); W of Cliff Head , 29°31.7'– 29°32.5'S 114°15.5' – 114°16.2'E, dead, 145 m (3 v, WAM) ; W of Cliff Head , 29°28'– 29°28.5'S 114°11' – 114°11.2' E, dead, 183 m (2 v, WAM) ; W of Dongara , 29°15'S 114°01'E, dead, 139–146 m (1 pr + many v, WAM; many v, WAM) ; W of Dongara , 29°11'– 29°12'S 113°52.2'– 114°01'E,alive, 137 m (2 pr + many v, WAM; 3 v, WAM; 2 pr, WAM) ; W of Dongara , 29°08.5' – 29°09'S 113°55.5'– 113°56'E, alive, 165 m (many v, WAM;2 pr, WAM) ; W of Dongara , 29°07.5'– 29°08'S 113°57.4'– 113°58'E, dead, 110 m (11 v, WAM) ; W of Dongara , 29°07.2'– 29°08'S 113°56.4' – 113°56.7'E, dead, 140.8 m (many v, WAM) ; SW of Geraldton , 29°05'S 113°56'E, dead, 99 m (14 v, WAM) ; SW of Bluff Point , 28°14'S 113°28'E, dead, 110 m (many v, WAM) ; NW of Bluff Point , 27°40'S 113°03'E, dead, 128 m (many v, WAM) ; Albrolhos , E of Zeewyk Channel, dead, 110–146 m (13 v, WAM) ; W of Shoal Point , 27°59'S 113°21' E, dead, 110 m (1 v, WAM) ; W of Bluff Point , 27°40'S 113°20'E, dead, 131 m (5 v, WAM) ; NW of Bluff Point , 27°18'S 113°16' E, dead, 99 m (1 v, WAM) ; off Zuytdorp Cliffs , 27°0'S 113°0'E, dead, 146 m (1 v, WAM) ; NW of Carnarvon , 24°04'S 112°39'E, dead, 183 m (1 v, WAM) ; SW of Point Cloates , 23°39'S 113°11'E, dead, 137 m (1 v, WAM) ; SW of Point Cloates , 23°25'S 113°14' E, dead, 187 m (1 v, WAM) .

Description. Shell up to c. 55 mm high, solid, moderately inflated, right valve slightly more convex than left, subcircular, weakly prosocoline, inequivalve, inequilateral, auricles almost equal in size and shape, moderately small; umbonal angle c. 90°; left valve whitish, cream or brownish, with magenta near the umbo of both valves and magenta maculations on plicae and costae, particularly towards dorsal margin, right valve otherwise uniform white.

Left valve sculptured with 3 prominent primary radial plicae and one weaker at each end of disc, with interspaces each broader than one plica; entire surface bearing secondary radial riblets.Auricles with 3–5 radial riblets. Surface bearing delicate, widely spaced, commarginal lamellae throughout, particularly preserved in radial interspaces, more closely spaced on auricles.

Right valve with 4 broad, flatter radial plicae, more prominent on centre of disc than on ends, with narrower interspaces than on left valve. Secondary radial riblets and commarginal lamellae as on left valve, but radial riblets weaker on plicae. Anterior auricle with 4–6 riblets, weaker or lacking on posterior auricle. Dorsal margin straight. Byssal notch large in specimens up to 5 mm high, decreasing in size with growth, shallow by 15 mm high, very small in adults; functional ctenolium well-developed in juveniles, lacking in adults. Hinge teeth weak.

Dimensions. Illustrated specimen: NSW, off Jervis Bay, 37–124 m ( AM C.347523): rv: H 47.4, L 49.6 mm; lv: H 46.9, L 48.8 mm; D 20.4 mm. Hedley (1901: 730) stated the dimensions of the holotype of Chlamys fenestrata as “height 20, length 20 mm ” .

Habitat. Living free (not byssally attached to substrates) on the continental shelf and in the upper bathyal zone (in 27–256 m) amongst rubble on soft sediment (sand and mud).

Distribution. All around southernAustralia from North West Cape, Western Australia (Well & Bryce, 1985: 160), Great Australian Bight, South Australia, Tasmania, Victoria, New South Wales, northwards to southern Queensland. Maximum depth range 73–256 m (Cotton, 1961: 102). Present material alive at 27– 165 m.

Remarks. Specimens from southwestern Australia ( Mesopeplum triggi morph) are somewhat atypical in having coarser secondary radial costae, but intermediates are also observed and other characters are identical to those of M. fenestratum . As also stated by Beu & Darragh (2001: 173) this form is part of the variation of M. fenestratum . Iredale (1924: 194) correctly pointed out that Dautzenberg’s (1902: 347) replacement name Chlamys hedleyi for Chlamys fenestrata is unnecessary, as C. fenestrata Hedley is not a homonym of Pecten fenestratus Forbes, 1844 .

Mesopeplum convexum from New Zealand differs from M. fenestratum in being larger, up to c. 70 mm high ( M. fenestratum up to c. 55 mm), more variable in shape (more variable in prosocline shape and more variable in inflation), more variable in sculpture (number and prominence of plicae and prominence of secondary costae), much more variable in coloration, and in retaining a short functional ctenolium and moderately deep byssal notch in adults (see also Beu & Darragh, 2001: 173; Dijkstra & Marshall, 2008: 72, figs 61A–D, 62). Specimens of Mesopeplum convexum vary clinally, southern specimens reaching a larger size and tending to be more weakly inflated and more finely sculptured than northern ones. Mesopeplum fenestratum is extremely conservative in sculpture and coloration compared with M. convexum .

Reeve’s (1853: pl. 22, fig. 84) illustration of Pecten roseopunctatus shows a species similar to Mesopeplum fenestratum , despite Cuming’s incorrect locality, “ Moluccas ”. The colour pattern also is similar to that of immature specimens of the common SE Australian form of M. fenestratum . Unfortunately, there is no type material of P. roseopunctatus in NHMUK. Dijkstra & Marshall (2008: 73) listed this name as a synonym of M. convexum , despite the unusual colour pattern. The specimen illustrated by Reeve (1853: pl. 22, fig. 84) has unusually coarse radial sculpture and a very prominent commarginal growth step, and closely resembles some of the more coarsely sculptured New Zealand specimens of M. convexum in these characters. We regard it as a synonym of M. convexum . The specimen of Mesopeplum convexum illustrated by Dijkstra & Marshall (2008: fig. 61C, D) from Stewart Island (NMNZ M155905) is here designated the neotype of Pecten roseopunctatus Reeve, 1853 , to attach this name permanently to M. convexum rather than replace the name M. fenestratum .