Lutetina, Velain, 1876

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 : 3209-3210

‘ Lutetina ’ capricornica n. sp.

( figures 112–117 )

HOLOTYPE: one (gold-coated) specimen from Grand Pate´, shell gravel, 17 m, 19 ‡ 39.307 ’ S, 63 ‡ 24.950 ’ E. NMW.Z.2001.061.00035.

PARATYPES: 20 valves as holotype, NMW .Z. 2001.061.00036.

Measurements (mm, L 6 H). Holotype: 1.97 6 1.72. Paratypes (only nine measured): 1.93 6 1.83, 2.59 6 2.30, 1.96 6 1.71, 2.30 6 2.14, 2.40 6 2.17, 2.33 6 2.08, 2.46 6 2.23, 1.92 6 1.71, 1.83 6 1.62.

Description. Shell to 2 mm in length. Fragile, hyaline. Equivalve. Equilateral. Outline subcircular, the anterior margin more acutely rounded than posterior margin. Lunule and escutcheon absent. Sculpture smooth with very weak concentric lines and growth stops. Hinge with well-developed teeth and a prominent sunken internal resilifer beneath the beaks; rv ( figure 116 ) with three cardinal teeth, one strongly developed, 3a and 3b laminar, posterior lateral PI large and projecting; lv ( figure 115 ) with A-shaped cardinal complex of 2a and 2b, posterior lateral as a marginal extension. Prodissoconch ( figure 117 ) discoidal, apex slightly sunken, somewhat vermiculate sculpture, 250 M m in diameter. Inner margins smooth but anterior dorsal of lv, and posterior dorsal of rv, with a comarginal groove. Adductor scars equal, relatively small.

Derivation of name. Latin suffix ica denoting place of belonging and Tropic of Capricorn, the known range of the species.

Comparisons. The generic placement of this taxon is tentative but was chosen because of the similarities in dentition and presence of an internal ligament. The teeth are well formed and the cardinal structures are more corbiculoid than the peg-like cardinal teeth seen in the Galeommatoidea. The internal ligament precludes this being a juvenile of any venerid but the Kelliellidae were considered. Most kelliellids have an external ligament but Alveinus does have a small internal fossette and co-marginal grooves. The cardinal arrangement, however, is less complex and the 3a/1/3b complex seen in the Rodrigues shells is absent from both Alveinus ojianus (Yokoyama, 1927) and A. miliacea (Oliver and Zuschin, 2001) . The closest approximation that we could reach was with Lutetina in that it has the 3a/1/3b complex and the A-shaped 2a/2b complex ( Chavan, 1969). It has, however, a well-developed PIII and PII is much longer. To date, Lutetina has been restricted to the Antarctic and its consideration here may seem unlikely. However, the generic and family-level relationships of many of these small species remain unresolved and we are not prepared to consider creating a new genus while so much of the Galeommatoidea and Cyamioidea remain understudied.

Figures

FIGS. 112–117. ‘Lutetina’ capricornica n. sp., holotype, NMW.Z.2001.061.00035: (112) external (MontageTM); (113, 114) internal right and left valves (SEM); (115, 116) hinge view, left and right valves (SEM); (117) prodissoconch (SEM).