PEGOPHYSEMINAE, Taylor & Glover & Smith & Dyal & Williams, 2011

Taylor, John D., Glover, Emily A., Smith, Lisa, Dyal, Patricia & Williams, Suzanne T., 2011, Molecular phylogeny and classification of the chemosymbiotic bivalve family Lucinidae (Mollusca: Bivalvia), Zoological Journal of the Linnean Society 163 (1), pp. 15-49 : 28

PEGOPHYSEMINAE – NEW SUBFAMILY

Except for Anodontia alba (type species of Anodontia ), all other species analysed that have been previously classified as Anodontia are separate on a highly supported long branch. Within this clade, the species previously classified into various subgenera of Anodontia , namely Loripinus , Pegophysema , Euanodontia , Cryptophysema , and Cavatidens also lie on long internal branches (most taxa included in 28S tree; Fig. 2 ). Because of their phylogenetic distinctive- ness we propose a new subfamily Pegophyseminae , and in consideration of the differences from Anodontia alba we elevate the subgenera listed above, together with Afrophysema and Bythosphaera (Taylor & Glover, 2005) , to full generic status. The type species of Pegophysema is Pegophysema schrammi (Crosse, 1876) , and an 18S sequence from this species (donated by D. Distel, specimen from Bermuda) grouped with other pegophysemine species in the analysis of Williams et al. (2004). A closely similar species from the Indo-West Pacific, Pegophysema philippiana , is included in the 28S and 18S trees herein.

Pegophyseminae are united by some unusual morphological characters, including thin, globular, smooth shells, a narrow edentulous hinge with an internal and laterally extended ligament in most species, and, anatomically, the presence of a mantle septum, digitate mantle gills, and extensive posterior mantle fusion ( Taylor & Glover, 2005).

Although the chronogram ( Fig. 5 ) suggests a late Cretaceous origin, there are no convincing records of Pegophyseminae-like bivalves in pre-Cenozoic rocks. Records for the Cenozoic are frequent, and contemporaneously in the Eocene of the Paris Basin and southern USA ( Cossmann & Pissarro, 1904 –06; Gardner, 1951), there were lucinids with characters of living Pegophyseminae such as Anodontia augustana Gardner, 1951 , ‘ Lucina ’ conili de Raincourt, 1877, and ‘ Lucina ’ parnensis Deshayes, 1857. Pre-Cenozoic species with a superficial resemblance to pegophysemines include the hydrocarbon seep-associated ‘ Cryptolucina ’ kuhnpassetensis Kelly, 2000 from the Cretaceous of Greenland, which is inflated and edentulous ( Kelly et al., 2000). From the Palaeozoic, Boyd & Newell (1979) compared the Permian Gigantocyclus zidensis Termier & Termier, 1977 , from the Permian of Tunisia with Anodontia , and the Devonian Paracyclas species , placed by Johnston (1993) into the family Paracyclidae , are similar in general shape to living taxa. There is insufficient evidence to include any of these genera in the Pegophyseminae .

Figures

Figure 2. Molecular phylogeny of the Lucinidae based on the single gene analysis of 28S rRNA produced by Bayesian analysis using MRBAYES. Support values are Bayesian posterior probabilities (%). Details of taxa are given in Table 1.

Figure 5. Chronogram generated by BEAST for species of Lucinidae, and calibrated using ten fossil records. The position of each calibration point is indicated by the numbers in circles (see the Material and methods and Discussion sections for details about the fossils). Error bars for node ages are the 95% highest posterior density intervals; clades with less than 50% support have no error bars; the root node has node bar trimmed by 50% for clarity. New subfamily divisions are shown on the right-hand side, with details presented in Table 3.