New Data on Warrana besnardi, a Tiny Bivalve Mollusk from the Southeastern Brazilian Coast

Abstract: Warrana besnardi (Klappenbach, 1963) is the single Atlantic species of the genus, and part of the family Condylocardiidae, composed of 21 genera and about 150 species. Recent availability of many well-preserved specimens allowed us to perform a detailed study of the shell of this species, using scanning electron microscopy and descriptions of the hinge structure, the larval shell, and the inner surface, complimenting and expanding previous taxonomic work. This morphological assessment included very small (0.5 mm in length), young individuals and larger (up to 1.5 mm in length), fully developed animals. Key new observations include the outline of the valves that varies with growth, with the young individuals being more equilateral, while the adults are obliquely inequilateral. The inner surface of the valves has microscopic pores, a feature already observed for other condylocardiids (but not for the Cuninae). The larval shell has the prodissoconch I (pI) averaging 220 µm in length, and the prodissoconch II (pII) 259 µm, measurements which suggest lecithotrophic development and that W. besnardi probably broods its young.