Parvamussium, Sacco, 1897

Dijkstra, H. H. & Maestrati, P., 2015, Pectinoidea (Bivalvia: Propeamussiidae and Cyclochlamydidae) from the southwestern Indian Ocean, African Invertebrates 56 (3), pp. 585-585 : 598-599

Key to species of Parvamussium in the southwestern Indian Ocean – Shell small, circular, semi-transparent, auricles nearly equal, byssal notch moderately deep, 13 internal ribs and one rudimentary.............................................................1

1 Shell 7.2 mm high, left valve smooth, umbonal part glossy, inequivalve, equilateral, auricles dissimilar in shape, colour whitish .................................... P. catillus sp. n.

– Shell small, subcircular, opaque, whitish, auricles unequal, byssal notch moderately deep, 10 internal ribs, adults also with rudimentary (1–7) .....................................2

2 Shell 10 mm high, left valve slightly more convex than right valve, inequivalve, almost equilateral, auricles dissimilar in shape, lv with weak radial sculpture, rv with regularly spaced commarginal lirae .................................................................. .................................................. P. formosum (Melvill in Melvill & Standen, 1907)

– Shell small, almost circular, semi-transparent, auricles unequal, lv creamy and reddish mottled, rv whitish, 10–11 prominent internal ribs, 1–5 rudimentary....................3

3 Shell 12 mm high, lv smooth, near periphery weak commarginal sculpture, byssal notch moderately deep .................................................................. P. kilburni sp. n.

– Shell small, subcircular, opaque, whitish, auricles almost equal in size, 9–10 internal ribs...........................................................................................................................4

4 Shell 13 mm high, both valves flattened, lv slightlY more convex than rv, inequivalve, inequilateral, lv with commarginal and radial sculpture, rv with regularly spaced slightly undulated commarginal lirae........................................ P. puillandrei sp. n.

– Shell small, almost circular, lv flattened, delicatelY radiallY sculptured, 9–10 internal ribs...........................................................................................................................5

5 Shell c. 10 mm high, lv stained and opaque, weakly radially and commarginally sculptured, rv almost smooth, whitish, 9–10 internal ribs, with a few rudimentary in some specimens................................................... P. scitulum (E.A. Smith, 1885)

– Shell small, subcircular, stained and opaque, lv slightlY more flattened than rv, auricles unequal, internal ribs 7–10 ........................................................................6

6 Shell 9 mm high, lv with prominent radial and weak commarginal sculpture, rv with regularly spaced commarginal lamellae................... P. siebenrocki ( Sturany, 1901)

– Shell small, subcircular, hyaline, glossy, white and orange stained, lv slightly more convex than rv, auricles unequal, rudimentary internal riblets laterally .................7

7 Shell 27 mm high, lv glossy and smooth, rv with faint commarginal closely spaced growth lines, near periphery prominent ........................................ P. strongae sp. n.

– Shell small, almost circular, opaque, whitish or creamy stained, valves almost equally convex, flattened, auricles unequal, 10 internal ribs with 1–6 rudimentarY ...........8

8 Shell 8 mm high, lv with prominent commarginal sculpture in early ontogeny, radial and commarginal sculpture in late growth stage with squamae on the intersection ........................................................... P. texturatum (Dautzenberg & Bavay, 1921)

– Shell small, almost circular, lv prominent reticulate sculpture, rudimentary internal riblets.......................................................................................................................9

9 Shell 5 mm high, opaque or semi-transparent, lv with 13–17 radial costae and widely spaced weaker commarginal sculpture, fine scales on intersections, auricles with prominent commarginal lamellae.............................................................................. .................................................. P. thyrideum (Melvill in Melvill & Standen, 1907)

– Shell small, almost circular, lv smooth and glossy, 10 internal ribs .....................10

10 Shell 10 mm high, lv opaque and whitish, lv only sculptured with delicate commarginal lamellae near ventral margin, 10 internal ribs, with a few rudimentary in some specimens....................................................... P. torresi (E.A. Smith, 1885)

– Shell small, almost circular, lv coarsely sculptured with vesicles, few rudimentary internal ribs............................................................................................................11

11 Shell 10 mm high, lv with commarginal lirae and radially arranged vesicles, few rudimentary internal ribs anteriorly and posteriorly ................................................. ................................................................................... P. vesiculatum Dijkstra, 1995

– Shell small, almost circular, lv with latticed sculpture in late growth stage, short internal ribs............................................................................................................12

12 Shell 7.5 mm high, opaque and whitish, lv in early growth stage with commarginal sculpture, rudimentary or short internal ribs............... P. vidalense ( Barnard, 1964)