Morphological and Genetic Diversity of the Wood-Boring Xylophaga (Mollusca, Bivalvia): New Species and Records from Deep-Sea Iberian Canyons Chiara Romano 1 *, Janet Ruth Voight 2 , Rocı´o Pe ´ rez-Portela 1 , Daniel Martin 1 1 Centre d’Estudis Avancats de Blanes (CEAB - CSIC), Blanes (Girona), Catalunya, Spain, 2 Integrative Research Center, The Field Museum, Chicago, Illinois, United States of America Abstract Deep-sea bivalves of the Xylophagaidae, a poorly known group, are obligate wood-borers. Deployment of wood in three submarine canyons off the Iberian coast, the Blanes and La Fonera Canyons (Mediterranean Sea) and the Avile ´s Canyon (Cantabric Sea, Bay of Biscay), lead to the discovery of four xylophagaid species in our samples. Xylophaga dorsalis (the dominant species), X. atlantica, X. cf. anselli and the new species X. brava, were identified on the basis of morphological data, and supported by a phylogenetic reconstruction based on the nuclear genes 18S rDNA and 28S rDNA and including several genus of Xylophagaidae. Genetic divergence between species of Xylophaga varied between genes, ranging from 0.5 to 4.0% for the 18SrDNA and from 4.1 to 16.6% for the 28SrDNA. Xylophaga brava sp. nov. appeared to be restricted to the Mediterranean and morphologically resembled the closely related X. cf. anselli from the Cantabrian Sea. However, they clearly diverged in two well-supported clades. Low levels of intraspecific variability and higher interspecific divergence between species also supported the existence of these two different species. Morphologically they differ in the number of cirri at the siphon openings, in the shape of the posterior shell and in the size of prodissoconch II. The new species is characterized by having weak, poorly mineralized mesoplax and siphons united throughout, covered by a periostracal, non- calcified tube; distinct proximal and distal siphons, the former translucent and soft, the latter muscular, with concentric rings. Xylophaga atlantica, previously known only from the western Atlantic, is reported for the first time in the Mediterranean Sea. Whether its presence in the Mediterranean indicates its natural distribution or reflects its recent introduction is unknown. Although xylophagaids have been previously reported to recruit heavily to wood deposited on the seabed, these four species colonized wood suspended 30 m above the seafloor. Citation: Romano C, Voight JR, Pe ´rez-Portela R, Martin D (2014) Morphological and Genetic Diversity of the Wood-Boring Xylophaga (Mollusca, Bivalvia): New Species and Records from Deep-Sea Iberian Canyons. PLoS ONE 9(7): e102887. doi:10.1371/journal.pone.0102887 Editor: Hector Escriva, Laboratoire Arago, France Received April 14, 2014; Accepted June 20, 2014; Published July 25, 2014 Copyright: ß 2014 Romano et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability: The authors confirm that all data underlying the findings are fully available without restriction. All the sequences used in this study were deposited and are available from GenBank. The type specimens were deposited in two museums. All the reference numbers are provided in the text of the paper. Funding: The study was carried out within the framework of the research projects PROMETEO (CTM2007-66316-C02-01/MAR), DOSMARES (CTM2010-21810-C03- 03), and BENTOMICS (CTM2010-22218-C02-01), funded by the Spanish Plan Nacional de Investigacio ´ n Cientı ´fica, Desarrollo e Innovacio ´ n Tecnolo ´ gica. This paper is a contribution to the Consolidated Research Group 2009SRG665 of the Generalitat of Catalunya. CR and RPP were supported by a JAE and a Juan de la Cierva posdoctoral fellowship respectively. The Malacological Society of London partially financed JV’s travel and stay in London and in Blanes. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * Email: cromano@ceab.csic.es Introduction Bivalves in the genus Xylophaga Turton, 1922 are obligate wood-borers in the deep sea. Their specialized shell carries denticles on their anterior beak to scrape wood, boring a hole in which they live, and their large, U-shaped diverticulum ofthe stomach accumulates wood shavings [1]. Symbiotic bacteria had been observed in their gills [2] but not yet cultivated and characterized. With limited sampling, the level of species diversity of xylophagaids is surprisingly high [3]. However, most species have been collected only once [4,5] and very little is known of their distribution, dispersal potential and other biological features. The Mediterranean Sea is among the world’s best known marine areas [6], however its deeper water fauna is largely unexplored. No species of Xylophaga have been formally described from Mediterranean specimens, although their presence had previously been reported without comment (e.g.[7,8]). In total, only five xylophagaid species are known from the entire eastern Atlantic Ocean, including the Mediterranean Sea [4]. Submarine canyons are widely distributed along the ocean margin and more closely spaced in the Mediterranean than in other areas [9].They contribute substantially to channelling matter from the shore to deep basins [10,11] and often sustain high biodiversity and biomass of many benthic faunal groups [12–15]. However, few studies on macrobenthic fauna have focused in Mediterranean submarine canyons [15,16]. The organic material concentrated on the submarine canyon floors may include sunken wood and other vegetation. Consequently canyons may offer ideal habitats for wood-dependent xylophagous bivalves, as suggested by the higher abundance of Xylophaga specimens inside a NW Mediterranean canyon than on the adjacent open slope [17]. Nevertheless, the taxonomic identification of the wood-boring PLOS ONE | www.plosone.org 1 July 2014 | Volume 9 | Issue 7 | e102887