To broaden the anatomical knowledge of marine bivalves, detailed gross anatomical studies of 20 species from the Florida Keys are presented, representing 19 families: Solemya occidentalis Deshayes, 1857 (Solemyidae), Propeleda carpenteri (Dall, 1881) (Nuculanidae), Arcopsis adamsi (Dall, 1886) (Noetiidae), Limopsis aff. cristata Jeffreys, 1876 (Limopsidae), Brachidontes exustus (Linnaeus, 1758) (Mytilidae), Isognomon alatus (Gmelin, 1791) (Isognomonidae), Hyotissa mcgintyi (Harry, 1985) and H. hyotis (Linnaeus, 1758) (Gryphaeidae), Pinna carnea Gmelin, 1791 (Pinnidae), Spondylus americanus Hermann, 1781 (Spondylidae), Plicatula gibbosa Lamarck, 1801 (Plicatulidae), Anomia simplex d'Orbigny, 1853 (Anomiidae), Carditamera floridana Conrad, 1838 (Carditidae), Entodesma beana (d'Orbigny, 1853) (Lyonsiidae), Codakia orbicularis (Linnaeus, 1758) (Lucinidae), Chama macerophylla Gmelin, 1791 (Chamidae), Lamychaena hians (Gmelin, 1791) (Gastrochaenidae), Polymesoda floridana (Conrad, 1846) (Cyrenidae), Laevicardium serratum (Linnaeus, 1758) (Cardiidae) and Scissula similis (J. Sowerby, 1806) (Tellinidae). These taxa represent various clades of the class Bivalvia and interface with broader regional and phylogenetic studies (e.g., the Bivalve Tree of Life,  http://www.bivatol.org, and Bivalves-in-Time-and-Space,  http://www.bivatol.org/bits), in which many serve as exemplar species in different contexts. These descriptions provide the most complete anatomical descriptions yet presented for all species, most especially for Solemya occidentalis, Limopsis aff. cristata, Hyotissa mcgintyi, H. hyotis, Carditamera floridana, Entodesma beana, Chama macerophylla and Polymesoda floridana, for which no or only minimal anatomical information has been previously published. This work presents the first anatomical description of any species of Scissula, based on S. similis. Two controversial characters — the promyal passages (in Hyotissa spp., in Anomia simplex noted here for the first time, and in Crassostrea reported in the literature) and the various kinds of posterior apertures and siphons present in the species examined and across the Bivalvia — emphasize the need for further comparative study to confirm homologies. Conspecificity of Brazilian material with that from the North American coast is clarified for all species, resulting in nine species being removed from Brazilian checklists (S. occidentalis, B. exustus, I. alatus, P. carnea, C. floridana, C. macerophylla, L. hians, L. serratum, and S. similis). Pertinent anatomical characters are summarized in a data matrix, and an analysis is provided to demonstrate the utility and resolving power of such characters (but from this limited taxon samp