Basterotia sp.

Oliver, P. Graham & Holmes, Anna, 2004, Cryptic bivalves with descriptions of new species from the Rodrigues lagoon, Journal of Natural History 38 (23), pp. 3175-3227 : 3211-3212

Basterotia sp.

( figures 118–121 )

Material examined. Two specimens from Grand Pate´, off Port Mathurin, shell gravel, 17 m, 19 ‡ 39.307 ’ S, 63 ‡ 24.950 ’ E. NMW.Z.2001.061.00038.

Description. Shell 3.4 mm in length. Thin, fragile. Inequilateral, beaks towards the anterior. Outline narrowly subovate, anteriorly reduced, slightly oblique; anterior dorsal margin short, sloping steeply to form a narrow yet rounded anterior margin; ventral margin gently curved but almost straight medially; posterior sloping steeply, gently curving to narrow but roundly pointed posterior ventral junction; posterior dorsal margin long, straight with a weakly defined escutcheon. Posterior slope angulate but rounded. Sculpture of concentric lines and growth marks and overall rather irregular. Hinge of lv ( figure 121 ) with a large projecting, upcurving anterior cardinal separated from a much smaller posterior tooth by a deep notch under the apex of the beak. The posterior projection possibly acting as a nymph for the small external ligament. Adductor scars indistinct; inner margin smooth. Shell colour white.

Comparisons. There are a number of Basterotia species described from the Indo-Pacific but most have a carinate posterior slope. In Rodrigues Basterotia borbonica ( Deshayes, 1863) is not uncommon and has a rounded posterior slope and similar dentition ( figure 123 ). It, however, like many other species, has a distinct granular surface and has a broader and more modioliform outline ( figure 122 ).

Figures

FIGS. 118–123. (118–121) Basterotia sp., NMW.Z.2001.061.00038: (118, 119) external and internal of left valve (MontageTM); (120) internal left valve (SEM); (121) hinge view, left valve. (122, 123) Basterotia borbonica, NMW.2000.086.00032 (SEM): (122) external left valve; (123) hinge view, left valve.