Upon reviewing the presentation of C. candida Leslie Crnkovic asked on Conch-L:

"Any idea as to why C. candita [sic] was moved to another genus? … i.e. - from Barbatia to Cucullaearca?"

The best explanation was provided by Harry Lee (significantly abbreviated here for simplicity):

"Arca candida was assigned to Barbatia early on, and those workers who saw affinities with Cucullaearca placed it in Barbatia (Cucullaearca) for many years as well - including Garvie (1996: 28), who described Cucullaearca as "elongate to obliquely subquadrate, subequal but generally much distorted, ventral valve margin deeply sinuated by a large byssal gape [my boldface]; cardinal area high, amphidetic; sculpture formed by fine to coarse subequal costae; hinge long, straight, teeth in continuous series in young, in adults divided in the middle by large gape, distal teeth conspicuously larger and oblique" and gave its range as Upper Cretaceous to Recent (warm seas).

Using mitocondrial DNA sequences, Marko (2002: see p. 2009 at [URL= http://mbe.oxfordjournals.org/content/19/1...5.full.pdf+html] http://mbe.oxfordjournals.org/content/19/1...5.full.pdf+html[/URL]) presented evidence that (Recent) Cucullaearca, conchological affinities notwithstanding, was only distantly related to Barbatia. I think this work was the basis for Bieler and Mikkelsen (2004: 510), Oliver and Holmes (2006), Mikkelsen & Bieler (2008: 52) and a few others** removing Cucullaearca from Barbatia and affording it full generic rank. I know it was why I did so (Lee, 2009: 19; species 31).

This splitting trend is not unanimous; Coan and Valentich-Scott (2012) cite Marko's work but summarily synonymize Cucullaearca with Barbatia !

** I lost my Huber (2010) to the elements a few months ago, so I cannot report on his treatment

Bieler, R., and P.M. Mikkelsen. 2004. Marine bivalves of the Florida Keys: a qualitative faunal analysis based on original collections, museum holdings and literature data. Malacologia, 46(2): 503-544.

Coan, E.V. and P. Valentich-Scott, 2012. Bivalve seashells of tropical West America: Marine bivalve mollusks from Baja California to Northern Peru, Part 1 & 2. Santa Barbara Museum of Natural History Monographs, 6. Santa Barbara Museum of Natural History: Santa Barbara, CA. xv + (1)-1258.

Garvie, C.L., 1996. The molluscan fauna of the Reklaw Formation, Marquez Member (Eocene: Lower Claibornian), in Texas. Bulletins of American Paleontology 111(352):1-140.

Huber, M., 2010. Compendium of bivalves. A full-color guide to 3,300 of the world’s marine bivalves. A status on Bivalvia after 250 years of research. ConchBooks, Hackenheim, Germany. 901 pp.

Lee, H.G., 2009. Marine shells of northeast Florida. Jacksonville Shell Club, Inc., Jacksonville, FL. 204 pp. + 19 color pls. May 28.

Marko, P.B., 2002. Fossil calibration of molecular clocks and the divergence times of geminate species pairs separated by the Isthmus of Panama. Molecular Biology and Evolution 19: 2005–2021.

Mikkelsen, P.M., and R. Bieler, 2008. Seashells of Southern Florida: Living Marine Mollusks of the Florida Keys and Adjacent Regions. Bivalves. Princeton University Press, Princeton, NJ. 503 pp.

Oliver, P.G. and A.M. Holmes, 2006. The Arcoidea (Mollusca: Bivalvia): a review of the current phenetic-based systematics. Journal of the Linnean Society 148: 237-251."

Here's Marko's CO1 ML tree topology: