Parvamussium scitulum (E.A. Smith, 1885 )

Dijkstra, H. H. & Maestrati, P., 2015, Pectinoidea (Bivalvia: Propeamussiidae and Cyclochlamydidae) from the southwestern Indian Ocean, African Invertebrates 56 (3), pp. 585-585 : 605-606

Parvamussium scitulum (E.A. Smith, 1885)

Fig. 4A–C

Amussium scitulum Smith, 1885: 312 , pl. 23 figs 4–4b. TYpe localitY: S of New Guinea (9°59'S 139°42'E),

- 51 m, dead, green mud, 10.ix.1874 (Challenger, stn 188).

Amusium (Propeamusium) [sic] scitulum var.? cmadoritinctum Kuroda, (1929–35) 1931: 77, figs 81–82.

Type locality: Japan, Kyushu, Kagoshima Prefecture, Yakushima Island .

Parvamussium scitulum: Dijkstra 2011: 42 , pl. 1016 figs 5, 6, 7, 8a–b; 2013: 21, pl. 3, figs 2a–d, pl. 4, fig.

10; Dijkstra & Maestrati 2012: 393; 2013 b: 474; Dijkstra & Janssen 2013: 192, figs 40–42.

Description: Shell fragile, up to 12 mm in height, subcircular, inequivalve, inequilateral, right valve more convex than left, auricles rather small and unequal, umbonal angle 115°–120°. Colour of left valve stained, opaque, right valve dull or semi-transparent whitish. Prodissoconch 200 µm long. Left valve verY weaklY inflated, weaklY sculptured with delicate, variable radial striations, somewhat stronger near posterior margin than elsewhere. Microscopic close-set commarginal striae developed on disc of some specimens, somewhat more widely spaced near umbonal area. Anterior auricle with prominent commarginal lamellae close to flank of disc, decreasing in prominence or absent near antero-dorsal margin; posterior auricle with fine radial and commarginal striations, almost absent from some specimens. Right valve either smooth or weakly sculptured with a few growth lines. Internal riblets extending to submarginal area, 9 or 10 in most specimens, some specimens with 1 or 2 rudimentary interstitial riblets. Resilifer triangular. Hinge line straight. Byssal notch narrow.

Type material examined: Amussium scitulum : Lectotype (lv) NHMUK 1887.2.9.3319/1; 6 paralectotypes (v) NHMUK 1887.2.9.3319/2-7, designated bY Dijkstra (1995: 31, figs 153–154).

Amusium scitulum cmadoritinctum: Kikuchi Shell Museum, Kuroda collection. [not examined]

Other material examined: NW MADAGASCAR: West of Nosy-Bé (13°25'S 47°57'E), - 71–158 m, dead, campaign Miriky, stn DW3230, 03.vii.2009 ( MNHN) ; In front of Mahajamba Bay (14°53'S 46°56'E), - 90–257 m, live, campaign Miriky, stn DW3245, 07.vii.2009 ( MNHN) . S MADAGASCAR: Manantenina (24°23'S 47°31'E), - 200–220 m, dead, expedition Atimo Vatae, stn DW3523, RV Nosy Bé 11, 01.v.2010 ( MNHN) ; Sainte Luce (24°43'S 47°32'E), - 296–307 m, dead, expedition Atimo Vatae, stn DW3534, RV Nosy Bé 11, 02.v.2010 ( MNHN) ; S of Faux Cap (26°03.2'S 45°32.1'E), - 98 m, dead, expedition Atimo Vatae, stn DW3550, RV Nosy Bé 11, 05.v.2010 ( MNHN) ; Fort-Dauphin (25°13.5'S 47°13.8'E), - 87–88 m, dead, expedition Atimo Vatae, stn CP3573, RV Nosy Bé 11, 08.v.2010 ( MNHN) ; SW Pointe Barrow (25°03'S 44°00'E), - 113–135 m, dead, expedition Atimo Vatae, stn DW3588, RV Nosy Bé 11, 11.v.2010 ( MNHN) . MOZAMBIQUE CHANNEL: Maputo transect (25°53'S 33°07'E), - 112–127 m, live, campaign Mainbaza, stn CP3130, 09.iv.2009 ( MNHN) . MOZAMBIQUE: Inhaca Island: N of the Channel (26°03.1'S 33°01'E), - 50–53 m, live, expedition Inhaca 2011, stn MD13 (= MD14), 30.xi.2011 ( MNHN) ; in front of Ponta Malengane (26°03.6'S 33°01.8'E), - 75 m, dead, expedition Inhaca 2011, stn MD26, 05.xii.2011 ( MNHN) ; in front of Ponta Malengane (26°03.6'S 33°03.8'E), - 130 m, dead, expedition Inhaca 2011, stn MD27, 05.xii.2011 ( MNHN) ; North Baixo Danae (25°50.9'S 33°03.1'E), - 50–53 m, dead, expedition Inhaca 2011, stn MD34, 08.xii.2011 ( MNHN) . Maputo: offshore (25°55'S 33°07'E), - 140–160 m, dead, s/n, dredge, leg. J. Rosado, xi.2011 ( MNHN) . SOUTH AFRICA: Zululand: Off Gipsy Hill (27°47.4'S 32°38.9'E), - 65–70 m, live, broken shell, NMDP stn ZK3, dredged RV Meiring Naudé, 08.vi.1988 ( NMSA E3656 ) .

Distribution and habitat: Southern Japan southwards to Australia, eastwards to the Austral Islands ( Dijkstra 2013: 22), and now also westwards into the Indian Ocean from the Mozambique Channel, northwestern and southern Madagascar and northeastern South Africa (new record). Living free sublittorally and upper bathyally (Dijkstra & Maestrati 2012: 393) on soft substrata (mixtured sediments of sand, muddy sand or mud with coral rubble or gravel). Present specimens live at - 53–112 m (minimum depth range). Remarks: Kuroda (1929 –1935: 77) described a possible new variation of the present species from Japan, which is more brightly coloured and much larger in size than the type material of Parvamussium scitulum . Smith (1885: 312) already suggested that the type specimens from Papua New Guinea are possible juveniles.

The present specimens from northwestern and southern Madagascar and the Mozambique Channel are indeed larger in size (up to 9 mm in height, typically 4.5 mm), more colourful (typically whitish), and some specimens have one more internal rib, but other morphological characters are identical to the type material .

Figures

Fig. 4. Parvamussium spp.: (A–C) P. scitulum (E.A. Smith, 1885): campaign Mainbaza, stn CP3130, (A) external view of the left valve, H = 6.2 mm, scale bar = 2 mm; (B) external view of the right valve, H = 5.7 mm, scale bar = 2 mm; (C) details of the left valve, H = 6.2 mm, scale bar = 0.1 mm (MNHN). (D–F) P.siebenrocki (Sturany,1901):campaign Mainbaza, stn CC3160, (D) external view of the left valve, H = 6.9 mm, scale bar = 2 mm; (E) external view of the right valve, H = 5.9 mm, scale bar = 2 mm; (F) details of the left valve, H = 6.9 mm, scale bar = 0.1 mm (MNHN). (G–M) P. strongae sp. n., holotype: campaign Miriky, stn DW3212, (G) external view of the left valve, H = 21.9 mm, scale bar = 1 cm; (H) internal view of the left valve, H = 21.9 mm, scale bar = 1 cm; (I) external view of the right valve, H = 17.4 mm, scale bar = 1 cm; (J) internal view of the right valve, H = 17.4 mm, scale bar = 1 cm; (K) prodissoconch of the left valve, H = 21.9 mm, scale bar = 0.2 mm; (L) details of the left valve, H = 21.9 mm, scale bar = 0.1 mm; (M) details of the right valve, H = 17.4 mm, scale bar = 0.1 mm (MNHN 39087).