Ctena Mörch, 1861

Glover, Emily A. & Taylor, John D., 2007, Diversity of chemosymbiotic bivalves on coral reefs: Lucinidae (Mollusca, Bivalvia) of New Caledonia and Lifou, Zoosystema 29 (1), pp. 109-181 : 134

Genus Ctena Mörch, 1861

Ctena Mörch, 1861: 201 .

TYPE SPECIES. — Lucina pectinata Carpenter, 1857 , non L. pectinata C. B. Adams, 1852 (replacement name Codakia (Jagonia) mexicana Dall, 1901 ) (subsequent designation by Dall et al. [1938]).

DIAGNOSIS. — Shells small to medium sized, sub-circular, umbones prominent. Radial ribs prominent, bifurcating and intercalating. Commarginal lamellae fine, forming scales on summits of ribs. Lunule long, heart-shaped, asymmetric with greater part in RV. Ligament short, set in oblique triangular resilifer.

REMARKS

Although Ctena and Epicodakia are frequently confused (see below under Epicodakia ), there are a number of characters that can be used to separate them. Ctena can be distinguished by the presence of irregular and bifurcating radial ribs compared to the more evenly spaced ribs that rarely bifurcate in Epicodakia ; the commarginal lamellae are also lower, more evenly and regularly spaced in Epicodakia , giving a scaly appearance. Ctena has a short ligament located in a more or less deeply inset resilifer on the hinge plate that differs from the mainly longer and external ligament of Epicodakia . The hinge plate of Ctena is always broader and more robust and the lunule is shorter and more heart-shaped. The juvenile shell of Ctena has far more prominent radial ribbing.

Molecular and morphological evidence also indicates that Ctena and Codakia are related ( Williams et al. 2004). However, Ctena species have smaller, more ovate shells and radial ribs that are typically bifurcated. The lunule in Codakia is much deeper, shorter and more triangular in outline compared to the shallower lanceolate lunule in Ctena . Unlike Ctena , the anterior lateral teeth in both left and right valves of Codakia lie extremely close to the cardinal teeth.