Propeamussium rosadoi, Dijkstra & Maestrati, 2015

Dijkstra, H. H. & Maestrati, P., 2015, Pectinoidea (Bivalvia: Propeamussiidae and Cyclochlamydidae) from the southwestern Indian Ocean, African Invertebrates 56 (3), pp. 585-585 : 592-593

Propeamussium rosadoi sp. n.

Fig. 1M–S

Etymology: After Mr José Rosado, an advanced amateur shell collector from Mozambique, who sampled and supplied much of the shell material for this investigation and participated in the three French campaigns herein mentioned.

Description: Shell up to 25 mm in height, fragile, most specimens transparent and some opaque, almost circular, inequivalve, slightly equilateral, left valve somewhat more inflated than right. Valves gaping laterallY. Auricles relativelY small and unequal in size (anterior: posterior ratio is 1.25: 1) and shape (anterior larger than posterior). Umbonal angle about 90°. Colour of left valve orange-brownish tinted, right valve paler, translucent whitish internal radial riblets. Prodissoconch 170 µm long. Left valve in early ontogeny smooth and glossy (c. 3 mm), then sculptured towards the central part of the disc with weak closely spaced radial riblets, in late growth stage smooth with a few delicate commarginal growth lines near the periphery, one or two delicate radial plicae near the posterior margin.Anterior auricle smooth and dull, posterior with microsculpture of very closely spaced radial scratches. Right valve sculptured with regularly spaced (c.

5 per mm) fine commarginal lirae.Anterior auricle laterallY with verY fine commarginal growth lines, posterior smooth with a narrow groove near the suture of the disc. Interior ribs 9, commencing in early ontogeny and extending submarginally, with one auricular on each side, ribs of right valve broader than of left valve. Resilifer triangular, elongate. Outer ligament rather broad. Hinge line straight. Small byssal notch, no ctenolium.

Dimensions: Holotype: Height 25.0 mm, width 24.9 mm, convexity 5.0 mm.

Type material: Holotype (pr) ( MNHN IM-2000-30115), paratypes ( MNHN IM-2000-30117, 16 pr, 5 lv, 2 rv; NMSA L9513/T3917, 2 pr; RMNH.5003911, 2 pr). Type locality: NW MADAGASCAR: In front of Mahajamba Bay (14°50'S 46°57'E), - 340–446 m, live, campaign Miriky, stn CP3248, 07.vii.2009.

Other material examined: MADAGASCAR: Northwest region : between Nosy-Bé and Banc du Leven (12°43'S 48°14'E), - 291–353 m, live, campaign Miriky , stn CP3209, 29.vi.2009 ( MNHN, 1 pr); between Nosy-Bé and Banc du Leven (12°51'S 48°12'E), - 341–345 m, dead, campaign Miriky , stn DW3226, 02.vii.2009 ( MNHN, 1 lv); West of Nosy-Bé (13°27'S 47°55'E), - 187–247 m, live, campaign Miriky, stn DW3234, 03.vii.2009 ( MNHN, 3 pr, 2 rv); in front of Mahajamba Bay (14°50'S 47°00'E), - 349–442 m, live, campaign Miriky, stn CP3247, 07.vii.2009 ( MNHN, 3 pr, 2 lv); in front of Mahajamba Bay (14°48'S 46°60'E), - 620–637 m, live, campaign Miriky, stn CP3249, 07.vii.2009 ( MNHN, 1 pr). SOUTH MADAGASCAR: Between Lokaro and Sainte Luce (24°53'S 47°28'E), - 184–203 m, dead, expedition Atimo Vatae, stn DW3515, RV Nosy Bé 11, 30.iv.2010 ( MNHN, 1 lv); Manantenina (24°23'S 47°32'E), - 395–407 m, dead, expedition Atimo Vatae, stn DW3525, RV Nosy Bé 11, 01.v.2010 ( MNHN, 5 rv); Manantenina (24°24'S 47°34'E), - 502–504 m, dead, expedition Atimo Vatae, stn DW3526, RV Nosy Bé 11, 01.v.2010 ( MNHN, 1 lv); Manantenina (24°23'S 47°32'E), - 305–313 m, dead, expedition Atimo Vatae, stn CP3527, RV Nosy Bé 11, 01.v.2010 ( MNHN, 1 rv); Manantenina (24°24'S 47°33'E), - 424–438 m, dead, expedition Atimo Vatae, stn DW3528, RV Nosy Bé 11, 01.v.2010 ( MNHN, 1 lv); Manantenina (24°24'S 47°33'E), - 402–407 m, dead, expedition Atimo Vatae, stn DW3529, RV Nosy Bé 11, 01.v.2010 ( MNHN, 1 lv, 2 rv); Sainte Luce (24°43'S 47°32'E), - 296–307 m, live, expedition Atimo Vatae, stn DW3534, RV Nosy Bé 11, 02.v.2010 ( MNHN); S Pointe Barrow (25°31'S 44°16'E), - 296–302 m, live, expedition Atimo Vatae, stn CP3583, RV Nosy Bé 11, 10.v.2010 ( MNHN, 1 pr) .

Distribution and habitat: Northwestern and southern Madagascar. Living bathyally on soft substrata of mud or muddy sand at a maximum depth range of - 187–637 m, minimum depth range - 247– 620 m.

Remarks: The most closely resembling species is Propeamussium rubrotinctum ( Oyama, 1951) recorded from southern Japan, South China Sea, Solomon Islands, Vanuatu Archipelago, New Caledonia, Fiji, Wallis and Futuna, and Tonga, live at - 210–869 m (Dijkstra & Maestrati 2012: 392), which differs morphologically from P. rosadoi in having a smaller size (20 mm in height, P. rosadoi 25 mm), in having a throughout smooth shell disc of the left valve ( P. rosadoi partially with a radial sculpture) and a very weak commarginal sculpture on the right valve ( P. rosadoi with a more prominent commarginal sculpture), in having 10 and sometimes several rudimentary internal ribs ( P. rosadoi 9 without rudimentary riblets), and in having a different colour (orange or whitish patches or dots, P. rosadoi uniform orange-brownish).

Another resembling species is Propeamussium steindachneri ( Sturany, 1901) recorded from the Red Sea, Gulf of Aden, Arabian Sea, and Gulf of Aden, live at - 363–479 m ( Dijkstra & Janssen 2013), which differs from P. rosadoi in having a smaller size (up to c. 15 mm in height, P. rosadoi c. 25 mm), in having a smooth left and right shell disc ( P. rosadoi radially (lv) and commarginally (rv) sculptured), and in having fewer and weaker internal ribs ( P. steindachneri 6, P. rosadoi 9).

Similar sized specimens of P. jeffreysii from the same stations as P. rosadoi could be easily mixed with P. rosadoi , but the former species could be differentiated from the latter species by the following characters, i.e. closer spaced with rudimentary interstitial internal ribs ( P. rosadoi wider spaced and lacking rudimentary interstitial internal ribs), a latticed sculpture on the left valve ( P. rosadoi a radial sculpture), a darker orange-brownish coloured left valve, and narrower internal ribs on the right valve ( P. rosadoi broader and more prominent).