Morphological and Genetic Diversity of the Wood-Boring Xylophaga (Mollusca, Bivalvia): New Species and Records From Deep-Sea Iberian Canyons

PLoS One. 2014 Jul 25;9(7):e102887. doi: 10.1371/journal.pone.0102887. eCollection 2014.

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 Avilés 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bivalvia / genetics*
  • Ecosystem
  • Genetic Variation*
  • Mediterranean Sea
  • Phylogeny*
  • RNA, Ribosomal, 28S / genetics

Substances

  • RNA, Ribosomal, 28S

Grant support

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 Investigación Científica, Desarrollo e Innovación Tecnológica. 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.