Molecular phylogeny of the family Pectinidae (Mollusca: Bivalvia) based on mitochondrial 16S and 12S rRNA genes Marco Barucca, a Ettore Olmo, a Stefano Schiaparelli, b and Adriana Canapa a, * a Istituto di Biologia e Genetica, Facolt  a di Scienze, Universit  a Politecnica delle Marche, via Brecce Bianche, I-60131 Ancona, Italy b Dipartimento Studio del Territorio e Risorse, University of Genoa, Italy Received 7 February 2003; revised 16 July 2003 Abstract Pectinidae is a large bivalve family characterised by almost circular, flat shells. Species are distributed worldwide and fall into three life-styles: swimming, byssally attached to hard substrates, and cemented to rocks with one valve. Despite these very different life strategies, pectinid shells are highly conservative in shape and offer few clues for the unravelling of phylogenetic issues. Con- sequently, phylogenetic studies based on morphological features have not yielded conclusive results. We thus set out to analyse partial sequences of mitochondrial 12S and 16S rRNA genes from 23 species of 16 genera with molecular techniques. The results are largely in contrast, both at the genus and the subfamily level, with the systematic classifications based on adult morphological characters, whereas they agree with the morphological classifications based on the more conserved non-adaptive features. Ó 2003 Elsevier Inc. All rights reserved. Keywords: Pectinidae; Bivalvia; mtDNA; 16S rDNA; 12S rDNA 1. Introduction The species of the family Pectinidae, or scallops, are characterized by circular or slightly oval shells and flattened valves; they live in a wide range of habitats, from shallow subtidal waters to 7000 m bottoms from the tropics to polar regions. Of the around 350 extant filter-feeding species (Hertlein, 1969), some live free in soft bottoms, where they can swim to escape predators by their ability to move over short distances by the rhythmic, rapid opening and closing of the valves; other forms are byssate, either as juveniles or throughout life, and others still live cemented to rocks as adults. Their morphological features, though useful for classification at the species level, provide scarce phylo- genetic information. Indeed, the attribution of several species at both the genus and the subfamily level within the current morphology-based systems is far from being univocal, as different authors give different degrees of importance to morphological features. Among the classification systems devised for the family Pectinidae, those of Korobkov (1960), Hertlein (1969), Vaught (1989), and Waller (1986, 1991, 1993) are the most comprehensive. Korobkov (1960) has classified scallops into four subfamilies: Pectininae, Chlamydinae, Amusiinae, and Palliolinae. Hertlein (1969) has adopted a classification into 11 suprageneric groups, of which Lentipecten, Amusium, Eburneopecten, Chlamys, Hin- nites, Decatopecten and Pecten contain the extant spe- cies. Vaught (1989) has subdivided them into the subfamilies Patinopectininae, Chlamydinae and Pectin- inae, the latter made up of four tribes, Hinnitini, De- catopectinini, Eburneopectinini, and Pectinini, and has included several species (belonging to Propeamussium, Parvamussium, Adamussium, and Amusium) in the fam- ily Propeamussiidae. Albeit they are substantially dif- ferent from each other, all these systems are based on the morphological features of adult shells, which do not always allow to evidence cases of evolutionary paral- lelism and convergence. To address the phylogenetic relationships among pectinids, Waller (1986, 1991, 1993) proposed a system based on microsculptural shell features and the mor- phological characteristics of juveniles. At this early * Corresponding author. Fax: +39-071-2204609. E-mail address: a.canapa@unian.it (A. Canapa). Molecular Phylogenetics and Evolution 31 (2004) 89–95 MOLECULAR PHYLOGENETICS AND EVOLUTION www.elsevier.com/locate/ympev 1055-7903/$ - see front matter Ó 2003 Elsevier Inc. All rights reserved. doi:10.1016/j.ympev.2003.07.003