Parvamussium thetidis (Hedley, 1902)

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 : 141-144

Parvamussium thetidis (Hedley, 1902)

Figs 12, 13

Amusium thetidis Hedley, 1902: 304 , fig. 49; Hedley & Petterd, 1906, 223, pl. 38, figs 18-19.

Amussium [sic] thetidis Hedley. –Pritchard & Gatliff, 1904a: 266.

Pecten (Amussium) cristatum [sic] Bavay, 1905a: 187, pl. 17, figs 2a–c (junior primary homonym of Pecten cristatus Bronn, 1828 ).

Amussium cristatellum Dautzenberg & Bavay, 1912: 36 , pl. 28, figs 5–8 (replacement name for Pecten (Amussium) cristatum Bavay, 1905 ).

Ctenamusium salacon Iredale, 1929: 164 ; Iredale & McMichael, 1962: 11.

Ctenamusium thetidis (Hedley) .– Iredale, 1929: 164, 188; Cotton & Godfrey, 1938: 98, fig. 84; Macpherson & Chapple, 1951: 145; Cotton, 1961: 102, fig. 88; Iredale & McMichael, 1962: 11.

Amussium texturatum Dautzenberg & Bavay. –Barnard, 1964: 432 (misidentification).

Propeamussium (Parvamussium) cristatellum (Dautzenberg & Bavay) .–Dijkstra, 1990a: 9.

Parvamussium cristatellum (Dautzenberg & Bavay) .– Dijkstra, 1991: 13, figs 28–32; Rombouts, 1991: 67; Dijkstra & Marshall, 1997: 80, pl. 3, figs 4–8, pl. 4, figs 1–2; Dijkstra & Kastoro, 1997: 261, figs 62–72; Dijkstra, 2001: 83; Spencer et al., 2009: 198; Dijkstra & Maestrati, 2010: 336; Dijkstra, 2011: 40, pl. 1015, figs 2–3b; Dijkstra, 2013: 18, pl. 2, figs 4a–5b, pl. 4, figs 7a–b.

Parvamussium thetidis (Hedley) .–Dijkstra, 1991: 14; Dijkstra, 1995b: 35, figs 99–102; Lamprell & Whitehead, 1992: [16], pl. 6, fig. 35; Dijkstra & Kastoro, 1997: 262, figs 83–89; Dijkstra & Maestrati, 2008: 95.

Type data. Amusium thetidis Hedley : holotype (rv) AM C.013210, 5 paratypes (v) AM C.171634. Type locality: Australia, New South Wales, 5–8 miles [8–13 km] off Port Kembla , 34°28'S 151°06'– 151°03'E, dead, 115–137 m (Thetis stn 49).

Figure 12. A–I, Parvamussium thetidis (Hedley) ; (A, B, G–I) separate valves, AM C.165516, c. 210 miles NE of Croker Island,Arafura Sea, NT, 08°18'S 133°58'E, 132 m; (C–F) syntypes of Ctenamusium salacon Iredale, AM C. 024345, 27 miles [43 km] E of Sydney Heads, NSW, 549 m (2 lv, light photos, copyright Australian Museum); rv exterior (A), rv auricles exterior (B), lv interiors (C, D, H), lv exteriors (E–G), sculpture of lv umbonal area (I). Scale bars represent 4 mm (A, H), 1 mm (B), 5 mm (C–G), 200 µm (I).

Amussium cristatum Bavay : lectotype (lv, Bavay, 1905a: pl. 17, fig. 2a) designated by Dijkstra & Kastoro (1997: 261) ZSI M3360/1; 2 paralectotypes (lv + rv, Bavay, 1905: pl. 17 figs 2b–c) ZSI M3360 /2–3. Type locality: “Masandam insulam” [= Andaman Islands , India], depth unknown.

Ctenamusium salacon Iredale : figured syntype (lv) AM C.024345, with a second syntype lv (Fig. 12C–F). Type locality: Australia, New South Wales, 27 miles [43 km] E of Sydney Heads , dead, 549 m.

Figure 13. Distribution of Parvamussium thetidis (Hedley) .

Additional material examined. — AUSTRALIA: QUEENSLAND: N Gulf of Carpentaria, 9°34'S 138°30'E, dead (4 v, C.338122); N Gulf of Carpentaria, 9°34'S 139°02'E, dead (2 v, C.338111); N Gulf of Carpentaria , 9°34'S 139°26'E, dead, 38 m (7 v, C.338123) ; N Gulf of Carpentaria , 10°35'S 140°28' E, dead, 46 m (8 v, C.338128) ; N Gulf of Carpentaria , 10°36' S 139°32'E, dead, 55 m (3 v, C.338124) ; N Gulf of Carpentaria , 10°51'S 139°32'E,dead, 55 m (6 v,C.338112) ; N Gulf of Carpentaria, 11°08'S 140°56' E,dead (1 v,C.338115);N Gulf of Carpentaria, 11°15'S 140°29'E,dead (3 v, C.338127); N Gulf of Carpentaria , 12°09'S 141°02'E, dead (2 v, C.338116); NE Gulf of Carpentaria , 12°09'S 141°02'E,dead, 50 m (3 v,C.338114) ; E Gulf of Carpentaria , 12°47'S 141°0' E, dead, 54 m (3 v,C.338113) ; E Gulf of Carpentaria , 13°10'S 140°35'E, dead, 64 m (9 v, C.338118) ; E Gulf of Carpentaria , 14°20'S 140°34'E, dead, 59 m (5 v, C.338119) ; S Gulf of Carpentaria , 14°29'S 139°32'E, dead, 66 m (1 v, C.338125) ; mid Gulf of Carpentaria , 14°51'S 139°47'E,dead, 66 m (1 v,C.338121) ; E Gulf of Carpentaria , 15°26'S 140°52'E,dead, 53 m (4 v,C.338120) ; S Gulf of Carpentaria , 15°29'S 139°31'E, dead, 49 m (1 v, C.338126) ; GBR, off Cairns , 16°34'S 146°15'– 146°13.6'E, dead, 192 m (10 v, C.338151) ; off Cairns ,16°36'– 16°35'S 146°15'– 146°14.3' E, dead, 110–201 m (1 v,C.338136) ; off Cairns ,16°36'– 16°35'S 146°14'– 146°13.8'E, dead, 172–197 m (18 v,C.338137) ; off Cairns ,17°09'– 17°07.4'S 146°42'– 146°42.8'E, dead, 243–253 m (1 v, C.157658) ; off Cairns , 17°09' – 17°09.5' S 146°42'– 146°41.8'E, dead, 311–329 m (2 v, C.338132) ; off Cairns , 17°11'– 17°12' S 146°38'– 146°37.7'E, dead, 143–150 m (1 v, C.338150) ; off Cairns , 17°13'S 146°48' E, alive, 1161 m (1 pr, C.338131) ; off Cairns , 17°14'– 17°13'S 146°40'– 146°38.7'E, dead, 150–176 m (10 v, C.157657) ; c. 200 ml W of Roebuck Bay , 18°33'S 119°08'E,dead, 128 m (3 v,C.165566) ; off Townsville , 18°49'S 146°58'E, dead, 34–35 m (1 v, C.157577) ; Swain Reefs, Bylund ( Gillett ) Cay , 21°43'S 152°25'E, dead, 27–37 m (many v, C.338155) ; SE of Swain Reefs , 22°26'– 22°20'S 153°17'– 152°17.6'E, alive, 187 m (1 pr, C.338135; 10 pr, many v, C.461377 [in part]) ; SE of Swain Reefs , 22°31'S 152°42'E,dead, 78 m (3 v,C.338170) ; SE of Swain Reefs , 22°32' S 152°33'E, dead, 92 m (2 v, C.157668; 3 v, C.157670) ; off Yeppoon , 22°42'S 151°37'E, dead, 68 m (4 v, C.338154) ; NE of Rockhampton , 22°50' S 151°39'E, dead, 64 m (1 v,C.338157) ; Capricorn Channel ,16.8 mls NE of North Reef, 23°08'S 152°12' E, dead, 115 m (many v, C.338109) ; Capricorn Channel , 23°08'S 152°16'E, alive, 155 m (2 pr + 12 v, C.338110) ; 18.5 ml E of North Reef , 23°11.5'S 152°14.5'E, alive, 188 m (1 pr + 2 v, C.165518 [in part]) ; Capricorn Channel , E of North West Island, 23°15'S 152°24'E, dead, 284 m (6 v, C.338146) ; Capricorn Group, North West Island , 23°18'S 151°42'E, dead, 18–36 m (5 v, C.338153) ; E of North West Island , 23°19'S 152°35'E, dead, 320 m (22 v, C.338145) ; near Heron Island , 23°23'S 151°56'E, dead, 40 m (1 v, C.338156) ; 24.5 mls E of Lady Musgrave Island , 23°33'S 152°37'E, dead, 339–348 m (18 v, C.338147) ; NE of Lady Musgrave Island , 23°38'S 152°45'E, dead, 365 m (15 v, C.338143) ; c. 25 mls E of Lady Musgrave Island , 23°44'S 152°49'E, dead, 348–357 m (many v, C.338148) ; E of Lady Musgrave Island , 23°51' S 152°34' E, dead, 175–200 m (3 v, C.157672;14 v, C.157673) ; E of Lady Musgrave Island ,23°52'– 23°51'S 152°42'– 152°41.7'E, dead, 296 m (many v, C.155799; 10 v, C.338134; many v, C.165563) ; Capricorn Channel , E of Lady Elliott Island, 24°0'S 153°06'E, alive, 476–531 m (1 pr + 22 v, C.338149) ; NE of Lady Elliot Island , 24°03'S 152°49'E, alive, 150 m (10 pr, C.157676) ; 20 mls N of Frazer Island , 24°22'S 153°17'E, dead, 192–229 m (1 v, C.338144) ; 20 mls N of Frazer Island , 24°23'S 153°17'E, dead, 100–128 m (1 v, C.338142) ; off Frazer Island , 24°57' S 153°37'E, dead, 210 m (many v, C.338141) ; off Maryborough , 25°47'S 153°33'E, dead, 64 m , 10 v (10 v, C.338152); off S end Frazer Island , 25°57' S 153°34'E, dead, 58–60 m (1 v, C.338140) ; off S end Frazer Island , 25°58'S 153°51'E, dead, 210–219 m (24 v, C.338138; 12 v, C.165560) ; off S end of Frazer Island , 26°0'S 154°0'E, dead, 732 m (1 v, C.338139) ; ESE of Noosa Heads , 26°34'S 153°40' E,dead, 128 m (15 v,C.338163) ; off Maroochydore , 26°41'S 153°38'E, dead, 200 m (11 v, C.338160) ; off Caloundra , 26°47' S 153°35' E, dead, 128 m (9 v, C.338164) ; NNE of Cape Moreton , 26°50'– 26°55'S 153°36'E, alive, 183 m (many, C.338165) ; NE of Cape Moreton Light , 26°54'– 26°57'S 153°32' – 153°35'E, dead, 115–119 m (many v, C.338166) ; NE of Cape Moreton , 26°55'S 153°33'E, dead, 124 m (4 v, C.308694) ; NE of Cape Moreton , 26°55' S 153°33' E, dead, 115–119 m (3 v, C.338158) ; NE of Cape Moreton , 26°55'S 153°33'E,alive, 115–124 m (many,C.338159; many, C.338169) ; E of Moreton Bay , 26°55'S 153°33' E, dead, 115–176 m (3 v, C.338168) ; off Cape Moreton , 27°0'S 153°35'E, alive, 128–183 m (many, C.338167) ; off N end of Moreton Bay , 27°01'S 153°36'E,dead, 128 m (10 v,C.338161) ; off Moreton Bay , 27°27'S 153°39'E, dead, 77 m (1 v, C.338162) ; off S end Frazer Island , 27°57'S 153°51'E,alive, 201 m (many v,C.338117; many v,C.165359) . NEW SOUTH WALES: 12.5 mls E of Cape Byron , 28°38'S 153°52'E, dead, 203 m (1 v, C.019806) ; 24 km E of Ballina , 28°49'S 153°51'E, dead, 185 m (20 v,C.338197) ; N of Coffs Harbour , 29°40' S 153°30' E,dead, 71 m (1 v,C.338178) ; off Korogoro Point , 31°11'S 153°13'E,dead, 220 m (2 v, C.338196) ; 38 km E of Forster , 32°22'S 152°57'E, dead, 247 m (2 v, C.338195) ; off Newcastle , 32°53'S 152°35' E, dead, 146–175 m (1 v, C.338181) ; off Newcastle , 32°58'S 152°41'E,dead, 951–1150 m , 3 v, dead(3 v,C.155843);E of Cape Three Points , 33°28'– 33°29'S 152°04'– 152°03'E,alive, 457–476 m (1 pr + 5 v,C.155817) ; off Broken Bay , 33°34'S 151°31'E, dead, 82–137 m (1 v, C.338189) ; off Botany Bay , 33°41' S 151°53'E, dead, 366 m (8 v, C.155806) ; 22 mls [35 km] E of Narrabeen, N of Sydney , 33°42'S 151°43'E, dead, 146 m (5 v, C.026071) ; off Sydney , 33°42'– 33°39'S 151°52'– 151°54' E, dead, 457 m (many v, C.155802) ; off Broken Bay , 33°43'S 151°50'E, dead, 270 m (6 v,C.155838) ; off Broken Bay , 33°43'S 151°40'E,dead, 143 m (8 v,C.338180) ; off Broken Bay , 33°44'S 151°48'E, dead, 263 m (11 v, C.155811) ; off Sydney , 33°46'S 151°43'E, alive, 176 m (6 pr + 12 v, C.155829) ; off Sydney , 33°46'S 151°43'E, dead, 176 m (14 v, C.155836) ; E of Sydney , 33°48'S 151°52'E, dead, 549 m (8 v,C.155826) ; 27.5 mls [44km]E of Sydney Heads , 33°50'S 151°49'E,dead, 457–459 m (1 v,C.024345; 5 v, C.338199) ; Sydney , 37 km E of South Head, 33°51'S 151°41'E, dead, 457 m (2 v, C.338198) ; off Sydney , 33°52'S 151°40'E, dead, 200 m (2 v, C.338194) ; off Sydney , 33°58' S 151°29'E,dead, 150 m (10 v,C.338186) ; Sydney, Malabar , c. 30 km E of Little Bay, 33°58'S 151°34'E, dead, 192–203 m (many v, C.338183) ; Sydney , 28 km E of Little Bay, 33°58'S 151°33'E, dead, 183–192 m (10 v, C.338184) ; off Sydney , 33°58' – 33°52'S 151°29'– 151°22'E, dead, 75–150 m (7 v, C.338185) ; Sydney S, off Cronulla , 34°03'S 151°09'E, dead (3 v, C.338190); E of Sydney, 34°03'S 151°37'E, dead, 295 m (4 v, C.338191) ; off Sydney , 34°04' S 151°37'E, dead, 384 m (12 v, C.338192) ; off Sydney , 34°04'S 151°37'E,dead, 393 m (10 v,C.338182) ; off Wattamolla , S of Sydney, 34°08'S 151°25'E, dead, 155 m (1 v, C.338188) ; S of Port Hacking , 34°09' S 151°26'E, dead, 205 m (1 v, C.338193) ; S of Sydney , 34°11'S 151°26'E, alive, 191–198 m (5 pr, C.343925) ; S of Sydney , 34°13'– 34°15.8'S 151°29'– 151°26.6'E, alive, 381–395 m (3 pr, C.343926) ; off Wollongong , 34°19'S 151°22'E, dead, 282 m (2 v, C.155825) ; off Port Kembla , 34°20'S 151°18'E, dead, 161 m (2 v, C.155835) ; 26 km E of Wollongong , 34°25'S 151°15'E, dead, 183 m (2 v, C.018135) ; 8–13 km off Port Kembla , 34°27'– 34°30'S 151°04'– 151°0.9'E,dead, 115–137 m (1 v,C.013210) ; 8–13 km off Port Kembla , 34°27'– 34°30' S 151°04'– 151°0.9' E, dead, 115–137 m (5 v, C.171634) ; off Nowra , 34°50'S 151°13'E, dead, 550 m (1 v, C.155821) ; off Nowra , 34°50'S 151°15'E, dead, 786–841 m (1 v, C.338179) ; 44 km E of Nowra , 34°55.79'– 34°56.06'S 151°08.06'– 151°07.86'E, alive, 429–466 m (13 pr [juv.], VM F.60249) ; off Jervis Bay , 35°05'S 151°02'– 151°10'E, dead, 400–1000 m (1 v, C.338187) . VICTORIA: off Gabo Island , 37°39' – 37°36'S 150°16'E,alive, 439 m (1 pr,C.343924) ; 53 km S of Cape Conran, Bass Canyon , 38°18'S 148°39' E, dead, 750 m (1 v, C.338200) . TASMANIA: Bass Strait, King Island , E of Grassy, 40°11' – 40°35' S 144°39'– 143°28'E, dead, 58–77 m (5 v, C.338354) ; off Cape Naturaliste , 40°50' S 148°46' E,dead, 399 m (1 v,C.338356) ; Maria Island,12 mls E Cape Mistaken , 42°42' S 148°17'E,dead, 695 m (2 v,C.338355) . SOUTH AUSTRALIA: off Beachport,dead, 366 m (2 v, SAM D19023) ; Cape Jaffa, dead, 238 m (2 v, SAM D19024) . WESTERNAUSTRALIA: W of Bluff Point , 37°40'S 113°12'E, dead, 174 m (1 v, WAM454.91 ) ; Recherche Archipelago , 34°09'S 121°27'E, dead, 81 m (3 v, C.338389) ; SW of Cape Naturaliste , 33°44'S 114°26' E, dead, 183–238 m (1 v, C.338386) ; SW of Cape Naturaliste , 33°35'S 114°31'E,dead, 176–183 m (6 v,C.338382) ; NW of Bunbury , 33°15' S 114°37'E, dead, 155 m (3 v, C.338407) ; NW of Bunbury , 33°15'S 114°32'E, dead, 201–228 m (many v, WAM427.91 ) ; W of Bunbury , 33°03'S 114°44'E, dead, 156 m (7 v, C.338378) ; off Bunbury , 33°0'S 114°41'E, dead, 170 m (3 v, C.338406) ; NW of Bunbury , 33°0'S 114°38'E, dead, 230–256 m (14 v, C.338411) ; NW of Bunbury , 33°0'S 114°37'E, dead, 200–221 m (many v, C.338410) ; SW of Mandurah , 32°45'S 114°47'E,dead, 220 m (8 v, C.338405) ; SW of Mandurah , 32°41'S 114°51'E,dead, 146–150 m (1 v,C.338408;1 v,C.165551) ; W of Garden Island , 32°15'S 115°07'E, dead, 210–212 m (11 v, C.338388) ; W of Garden Island , 32°15'S 115°03'E, dead, 250–258 m (14 v,C.338409) ; W of Garden Island , 32°15'S 115°06'E,dead, 176–182 m (12 v, C.338387) ; W of Rottnest Island , 32°0'S 115°15'E, dead, 146–150 m (4 v, C.338401) ; W of Rottnest Island , 31°59'S 115°13'E,dead, 201–214 m (13 v,C.338395) ; W of Rottnest Island , 31°50'S 115°03'E, dead, 256–320 m (7 v, C.338414) ; NW of Rottnest Island , 31°45' S 115°09'E, dead, 144–150 m (5 v, C.338396) ; NW of Rottnest Island , 31°45'S 115°02'E, dead, 265–276 m (6 v, C.338390; 1 v, C.165554; 1 v, C.165555) ; off Rottnest Island, Direction Bank , 31°44'S 115°12'E, dead, 138 m (2 v, C.338397) ; NW of Rottnest Island , 31°44'S 115°03'E,dead, 183–192 m (4 v,C.338391) ; off Rottnest Island , 31°42'S 115°08' E,dead, 150 m (2 v,C.338419) ; off Rottnest Island , 31°41'S 115°05'E, dead, 164 m (2 v,C.338418) ; off Rottnest Island , 31°38'S 115°08'E, dead, 140 m (2 v, C.338420) ; W of Guiderton , 31°34'S 115°03'E, dead, 135 m (3 v, C.338403) ; W of Rottnest Island , 31°0'S 114°52'E, dead, 256 m (2 v, C.338413) ; W of Rottnest Island , 31°0'S 114°51' E, dead, 256 m (7 v, C.338416) ; W of Rottnest Island , 31°0' S 114°51' E, dead, 283–320 m (11 v, C.338415) ; W of Rottnest Island , 30°59' S 114°51'E, dead, 229 m (9 v, C.338412) ; WNW of Lancelin , 30°58'S 114°53'E, dead, 154 m (12 v, C.338392) ; WNW of Lancelin , 30°58'S 114°47'E, dead, 289 m (2 v, C.338394) ; NW of Green Head , 30°37'S 114°38'E, dead, 128–140 m (1 v, C.338404) ; W of Cervantes Island , 30°33'S 114°40'E, dead, 192–196 m (14 v, C.338398) ; W of Cervantes , 30°33'S 114°32'E,dead, 154 m (7 v,C.338400) ; off Cervantes Island , 30°32' S 114°41'E, dead, 238–247 m (9 v, C.338399) ; NW of Cervantes I., 30°30'S 114°38'E, dead, 192–256 m (15 v, C.338381) ; W of Jurien Bay , 30°19'S 114°37'E, dead, 148 m (1 v,C.338359) ; off Jurien Bay , 30°08'S 114°30'E, dead, 223–245 m (13 v, C.338417) ; NW of Green Head , 29°58'S 114°27'E,dead, 197–219 m (3 v,C.338402) ; SW of Dongara , 29°49'S 114°24'E, dead, 135 m (1 v, WAM455.91 ) ; NW of Beagle Island , 29°43'S 114°20'E, dead, 183 m (3 v, C.338421) ; W of Beagle Island , 29°35' – 29°36'S 114°17' E – 114°20'E,dead, 163 m (2 v,C.338380) ; WSW of Dongara , 29°30'S 114°12'E, dead, 146–155 m (1 v, WAM436.91 ) ; off Pelsaert Bank , 29°28'S 114°11'– 114°11.2'E, dead, 183 m (2 v, C.338379) ; W of Dongara , 29°20.8'S 114°05.7' E, dead, 192–219 m (2 v, WAM497.91 ) ; Rottnest Shelf , 28°10.62'S 113°23.17'E, dead, 154 m (1 v, WAM 12523; 1 v, WAM 12524) ; NW of Bluff Point , 27°40'S 113°03' E, alive, 128 m (1 pr, WAM453.91 ) ; W of Carnarvon , 24°59'S 112°27'E, alive, 130 m (1 pr, WAM477.91 ; 3 v, WAM478.91 ) ; NNW of Dampier , 19°34'S 116°08'E,dead, 101 m (2 v, WAM490.91 ) ; North West Shelf , c. 170 mls W of Port Hedland, 19°29'S 116°01'E, dead, 137 m (8 v, C.338358) ; 72 n. ml NNW of Dampier ,19°28.9'– 19°29.0'S 116°29.4'– 116°29.0'E,alive, 110 m (4 pr + many v, C.157686) ; North West Shelf , 115 mls NW of Port Hedland, 19°26'S 117°14'E, dead, 91 m (8 v, C.338375) ; North West Shelf , c. 190 mls NW of Port Hedland, 19°25'S 115°51'E,dead, 256 m (4 v,C.338376) ; North West Shelf , c. 190 mls NW of Port Hedland, 19°24'S 115°52'E, dead, 238 m (8 v, C.338377) ; North West Shelf , c. 90 mls N of Port Hedland, 19°07'S 118°15'E, dead, 88 m (3 v, C.338372) ; 78 n. ml NNE of Port Hedland , 19°04.6'– 19°03' S 118°47.4'– 118°06'E, dead, 82 m (1 v, C.157714) ; 85 n. ml NNW of Port Hedland , 19°00.8'S 118°01.3'E, dead, 112 m (many v, C.157688; many v, C.157687) ; 85 n. ml NNW of Port Hedland , 19°00.4' – 19°00.3'S 118°01.0'– 118°01.1'E,dead, 116–120 m (2 v, C.165204 [in part]) ; North West Shelf , c. 120 mls NW of Port Hedland, 18°54'S 117°27'E, dead, 183 m (2 v, C.338374) ; 94 n. ml NNE of Port Hedland , 18°48'S 119°0'E, dead, 92–94 m (many v,C.157690) ; 100 n. mls NW of Port Hedland , 18°47'S 117°58'E, dead, 154 m (15 v, WAM458.91 ; 12 v, WAM459.91 ) ; North West Shelf , 110 mls N of Port Hedland, 18°46'S 119°17'E, dead, 106 m (3 v, C.338369) ; North West Shelf , c. 140 mls W of Broome, 18°42'S 120°06'E, dead, 90 m (2 v, C.338373) ; North West Shelf , c. 120 mls N of Port Hedland, 18°40'S 119°23'E, dead, 117 m (17 v, C.338367; 2 v, C.165564) ; N of Port Hedland , 18°40'S 117°55' E, dead, 150 m (3 v, C.157678; 25 v, C.157680) ; North West Shelf , c. 200 mls W of Roebuck Bay, 18°33'S 119°08'E,dead, 128 m (12 v,C.338370) ; North West Shelf , c. 180 mls W of Broome, 18°25'S 119°50' E,dead, 115 m (1 v, C.338366) ; 114 n. mls N of Port Hedland, 18°25'S 118°22' E (4 v, WAM463.91 ); North West Shelf,130 mls N of Port Hedland , 18°13'S 118°37'E,dead, 229 m (4 v,C.338371) ; S of Rowley Shoals ,dead, 266 m (6 v, WAM 469.91 ; 2 v [atypical], WAM471.91 ) ; North West Shelf , c. 230 mls W of Broome, 18°0'S 118°56'E,dead, 261 m (6 v, C.338368;5 v,C.157716) ; North West Shelf , c. 135 mls NW of Roebuck Bay, 17°34'S 120°22'E, dead, 188 m (2 v, C.338365) ; North West Shelf , c. 100 mls NW of Broome, 16°58'S 120°47' E, dead, 194 m (16 v, C.338357; 4 v, C.165568) ; North West Shelf , c. 150 mls W of Cape Leveque, 16°16'S 120°45'E, dead, 330 m (5 v, C.338364) ; North West Shelf , c. 110 mls NW of Cape Leveque, 15°53'S 121°28'E, dead, 95 m (1 v, C.338363) ; North West Shelf , c. 170 mls N of Broome, 15°27' S 121°31'E, dead, 210 m (3 v, C.338362) ; c. 210 mls N of Broome , 14°50'S 121°49'E, dead, 230 m (2 v,C.338361) ; N of Cape Leveque , 14°07'S 122°52'E, dead, 256 m (12 v, C.338360) . NORTHERN TERRITORY: Arafura Sea , 386 km N of Goulburn Island, 8°02'S 133°50'E, dead, 108 m (6 v, C.338090) ; Arafura Sea , c. 210 ml NE of Croker Island, 8°18'S 133°58'E,dead, 132 m (many v,C.165516) ; Arafura Sea , 8°09'S 134°50'E, alive, 115 m (1 pr, C.165228) ; Arafura Sea , c. 250 mls NE of Croker Island, 8°09'S 134°50'E,dead, 115 m (5 v,C.338083) ; Arafura Sea , N of Wessel Islands , 8°36'S 135°08'E, dead, 82 m (1 v, C.338082;1 v, C.338129) ; Arafura Sea , 320 km N of Goulburn Island, 8°39'S 133°34'E,dead, 192 m (3 v,C.338089) ; Arafura Sea , c. 200 mls NW of Wessel Islands , 8°39'S 135°21'E, dead, 65 m (3 v, C.338085) ; Arafura Sea , 365 km N of Milingimbi Island, 8°48'S 134°58'E, dead, 100 m (8 v,C.338086) ; Arafura Sea , c. 180 mls NW of Wessel Islands , 8°56'S 135°25' E,dead, 73 m (2 v,C.338084) ; Arafura Sea , c. 250 mls NE of Croker Island, 9°11'S 135°43'E, dead, 60 m (9 v, C.338130) ; Arafura Sea , 230 km N of Goulburn Island, 9°18'S 133°38'E,dead, 135 m (8 v,C.338088) ; Arafura Sea , 200 km N of Melville Island, 9°23'S 131°22'E,dead, 215 m (8 v,C.338095) ; Arafura Sea , 180 km N of Croker Island, 9°24'S 133°02'E,dead, 125 m (5 v, C.338092) ; N of Arnhem Land , 9°30'S 135°50'E,dead (10 v, C.338099); Arafura Sea, 160 km N of Melville Island, 9°45' S 131°19'E, dead, 124 m (1 v, C.338096) ; Arafura Sea , c. 110 ml N of Melville Island, 9°34'S 131°22'E, dead, 135 m (9 v, C.165562) ; Arafura Sea , 150 km N of Cobourg Peninsula, 9°45'S 132°04'E, dead, 108 m (4 v, C.338094) ; Arafura Sea , 150 km NW of Melville Island, 9°53'S 130°02'E, dead, 205 m (21 v, C.338097) ; Arafura Sea , c. 100 ml N of Croker Island, 9°30' S 132°34'E, 124 m (many v,C.165537) ; Darwin, 32 km off Point Charles , 12°10'S 130°22'E, dead, 22 m (1 v, C.338103) ; N of Arnhem Land , 10°01'S 135°48'E,dead (5 v,C.338100); Arafura Sea, 67 km NE of Croker Island, 10°36'S 132°56'E, dead, 62 m (1 v, C.338093) ; 68 km NE of Croker Island , 10°39'S 133°05'E, dead, 62 m (17 v, C.338091) ; 91 km N of Goulburn Island , 10°42'S 133°36'E, dead, 58 m (4 v, C.338087) ; N of Arnhem Land , 10°48'S 136°30' E, dead, 50 m (1 v,C.338101) ; SW Gulf of Carpentaria , 13°59'S 137°31'E,dead, 55 m (1 v,C.338098) ; W Gulf of Carpentaria , 13°57' S 137°48' E, dead, 59 m (2 v, C.338102.— INDONESIA: Ceram, Piru Bay , 3°10'S 128°08'E, dead (10 v, C.165538) . — SOLOMON ISLANDS : W coast Malaita Island, off Laulesi , 8°53'S 160°45' E, dead, c. 366 m (1 v, C.165434) . CORAL SEA: North East Herald Cay , 16°56'S 149°11'E, dead, 5–7 m (4 v, C.338457) . — NEW CALEDONIA:S of Ile des Pins , 22°50'S 167°34'E,dead, 274 m (1 v,C.165440) . TASMAN SEA: Lord Howe Rise , 31°37'S 159°13'E, dead, 51–55 m (1 v, C.338456).

Description. Shell fragile, small, up to c. 10 mm high, opaque, inequivalve, inequilateral, left valve slightly more convex than right, auricles unequal in size, umbonal angle c. 95°, prodissoconch c. 210 µm high. Left valve cream, some specimens with white spots; right valve uniform whitish. Internal riblets 8–10, most specimens with 10, some specimens with rudimentary interstitial riblets, plus 1 or in a few specimens 2 auricular riblets. Riblets fine at first, becoming more prominent distally near ventral marginal.

Left valve sculptured with unevenly spaced radial riblets, commencing at c. 1 mm shell height, enlarging to ventral margin. Commarginal lamellae rather delicate, variable, close-set to more widely spaced, traversing radial riblets.

Auricles with fine, closely spaced commarginal lamellae, somewhat weaker on posterior than anterior auricle. Dorsal margin straight.

Right valve with regular, rather widely spaced commarginal lirae. Anterior auricle with closely spaced commarginal lamellae and 1–3 weakly developed radial riblets near byssal fasciole, posterior auricle with commarginal lamellae only. Dorsal margin slightly raised at ends, with small scales along margin. Resilifer triangular. Byssal notch narrow.

Habitat. Living on the continental shelf and in the bathyal zone, free on soft sediment (sand, muddy sand or sandy mud).

Distribution. Philippines, 80–150 m [as Parvamussium cristatellum ] (Dijkstra, 2011); Eastern Indonesia, 230–467 m [as P. cristatellum ] (Dijkstra, 1991; Dijkstra & Kastoro, 1997); Chesterfield Islands , Coral Sea, 500–540 m; Norfolk Ridge, 573–650 m; Loyalty Islands , 310–350 m (dead); Vanuatu, 450–550 m (dead) [as P. cristatellum ] (Dijkstra, 1995b); Kermadec Islands , 256–549 m (dead) [as P. cristatellum ] (Dijkstra & Marshall, 1997); Norfolk Ridge, 569–616 m; Fiji, 390–410 m; Tonga, 351–450 m (dead) (Dijkstra & Maestrati, 2008); Austral Islands , 140–750 m (dead) [as P. cristatellum ] (Dijkstra & Maestrati, 2010). Maximum depth range of live-taken specimens is 230–650 m, from Australia 110–1161 m.

Remarks. The external sculpture of the left valve of Parvamussium thetidis is extremely variable. The primary radial riblets vary in prominence from strongly developed to very weakly developed or even lacking on the central part of the disc and are unevenly spaced. The commarginal lamellae also vary in spacing from very closely to more widely set. All these variations are observed in the abundant material from around Australia. This includes material indistinguishable from the specimens previously identified as P. cristatellum (Dautzenberg & Bavay, 1912) and Ctenamusium salacon Iredale, 1929 , which we therefore regard as a synonyms of P. thetidis .

The northwestern Indian Ocean species Parvamussium siebenrocki ( Sturany, 1901) and Parvamussium formosum (Melvill in Melvill & Standen, 1907) are very closely similar to the present species (see Dijkstra & Marshall, 1997: 80) and could be morphs or even synonyms of the one species, in which case the earliest name for this species would be P. siebenrocki . However, the distribution and range of variation require further study before this is accepted.