Kalolophus antillarum ( Reeve, 1842 )

Devries, Thomas J., 2016, Fossil Cenozoic crassatelline bivalves from Peru: New species and generic insights, Acta Palaeontologica Polonica 61 (3), pp. 661-688 : 681-682

Kalolophus antillarum ( Reeve, 1842)

Fig. 3A, B .

1832 Crassatella undulata sp. nov.; Sowerby, 1832: 56, not Say 1824, not Lamarck 1801.

1842 Crassatella antillarum sp. nov.; Reeve 1842: 44.

1843 Crassatella antillarum ; Reeve 1843: vol. 1, pl. 2: 8.

1917 Crassatella digueti sp. nov.; Lamy 1917: vol. 62, 2, 7.

1931 Crassatellites antillarum (Reeve) ; Grant and Gale 1931: 271, pl. 13: 7a, b.

1961 Eucrassatella (Hybolophus) diqueti [sic] (Lamy); Olsson 1961: 180, pl. 25: 2.

1964 Eucrassatella (Hybolophus) antillarum (Reeve) ; Weisbord 1964: 194, pl. 25: 9, 10.

1979 Eucrassatella (Hybolophus) antillarum (Reeve) ; Gibson-Smith and Gibson-Smith 1979: 28.

1984 Eucrassatella antillarum ( Reeve, 1842) ; Coan 1984: 160, figs. 12−16.

2012 Eucrassatella antillarum ( Reeve, 1842) ; Coan and Valentich-Scott 2012: 398, pl. 130.

See Weisbord (1964) and Coan (1984) for more extensive synonymies.

Holotype: British Museum of Natural History , Zoology, 1953.4.15.10.

Type locality: Isla Margarita, West Indies.

Type horizon: Recent.

Material.— UWBM 101884 , Coché , near Margarita Island, Venezuela, on muddy sand at depth of 20−25 m, Recent, L 68.6, H 49.0, T 12.1 ; UWBM 101885 , Canal de Adentro Island , Bahia de Panama, western Panama, from depth of 80 m, Recent, L 46.6, H 31.1, T 9.9 .

Emended diagnosis.—Exterior of shell with exclusively irregular commarginal growth lines.

Description.—Shell to 90 mm long, sharply ovate anteriorly, posterior variably produced, beak located two-fifths of distance from anterior L:H ratio 1.4−1.6, T:H ratio 0.2, maximum inflation ventral to beak, nearly as inflated posteriorly as medially. Anteriodorsal profile straight, posteriodorsal profile concave. Anterior margin rounded, ventral margin broadly rounded and slightly constricted posteriorly, posterior margin bluntly truncate. Angular primary posterior ridge diverging 20° from posteriodorsal margin and weakly sulcate on both sides, weaker angular secondary posterior ridge midway between primary posterior ridge and escutcheon. Lunule elongate, sometimes narrow, half the length of anteriodorsal margin. Escutcheon less than half the length of posteriodorsal margin, wider than lunule. Beak and umbo orthogyrate to opisthogyrate. Umbo flattened, with broad undulations, not entirely commarginal and fading posteriorly and anteriorly. Remainder of exterior with irregular commarginal growth lines. Left anterior cardinal tooth narrow, wedge-shaped, inclined anteriorly 50−60°, extending from vmHP to beak, separated entirely from lunule by groove. Left posterior cardinal tooth narrower, wedge-shaped, inclined anteriorly 20−30°. Right anterior pseudocardinal tooth narrow, straight, nearly coincident with lunule margin. Right cardinal tooth straight, wedge-shaped, inclined anteriorly 40°. Right posterior pseudocardinal tooth lamellar, diverging 20° from midpoint of cardinal tooth. Inner ventral margin smooth.

Remarks.— Kalolophus antillarum had become established in the Pacific and Atlantic during the Pliocene ( Grant and Gale 1931; Weisbord 1964; Gibson-Smith and Gibson-Smith 1979). Specimens of the modern sympatric crassatelline in the Pacific Ocean, Hybolophus gibbosus , are more inflated anteriorly, more constricted posteriorly, and their two posterior ridges are more closely spaced, thereby creating a posterior margin that is almost pointed. Specimens of the modern sympatric congener in the Atlantic Ocean, K. speciosus , resemble those of K. antillarum in most respects, but the exterior is entirely covered with regularly spaced and pronounced commarginal ribs ( Fig. 3H 1 ).

Stratigraphic and geographic range.—Pliocene–Pleistocene, Gulf of California, Venezuela. Recent, Gulf of California to Guayas, Ecuador, and Venezuela.

Figures

Fig. 3. Crassatelline bivalves from Central and South America. A, B. Kalolophus antillarum (Reeve, 1842). A. UWBM 101885, Recent, Pacific coast of Panama; exterior (A1) and interior (A2) of left valve. B. UWBM 101884, Recent, Venezuela; dorsal view of paired valves, anterior at right. C. Hybolophus berryi (Spieker, 1922), USNM 562399, early Miocene, lower Zorritos Formation, Zorritos, Peru; exterior of left valve (C1), dorsal view of paired valves C2), anterior at right. D. Hybolophus elassa Woodring, 1982, USNM 647424, late Miocene, Gatun Formation, Panama; exterior of left valve.E. Kalolophus mediamaricanus (Brown and Pilsbry, 1913), USNM 647421, early Miocene, La Boca Formation, Panama; exterior of right valve. F. Kalolophus sp., USNM 647423, late Miocene, middle Gatun Formation, Panama; exterior (F1) and interior (F2) of left valve. G. Kalolophus jamaicensis (Dall, 1903), USNM 135683, Pliocene, Bowden Formation, Jamaica; interior of left valve. H. Kalolophus speciosus (Adams, 1854), SBMNH 140817, Recent, Panama City, Florida; exterior (H1) and interior (H2) of left valve; dorsal view of paired valves (H3), anterior at right. Scale bars 10 mm.

Fig. 1. Forearc basins in Peru with crassatelline-bearing Cenozoic deposits. A. Talara Basin of northern Peru. B. Location of three crassatelline-bearing Peruvian forearc basins. C. East Pisco Basin of south-central Peru. Dashed black line marks the inferred boundary between the East and West Pisco basins. D. The much smaller Sacaco Basin of southern Peru.