title: Mantle margin morphogenesis in Nodipecten nodosus (Mollusca: Bivalvia): new insights into the development and the roles of bivalve pallial folds.
abstract: BACKGROUND
  Despite extensive knowledge on bivalve anatomy and development, the formation and differentiation of the mantle margin and its associated organs remain largely unclear. Bivalves from the family Pectinidae (scallops) are particularly promising to cast some light on these issues, because they exhibit a complex mantle margin and their developmental stages are easily obtained from scallop farms. We investigated the mantle margin of the scallop Nodipecten nodosus (L. 1758) during larval and postmetamorphic development.
  
  
  METHODS
  A thorough analysis of the mantle margin development in Nodipecten nodosus, from veliger larvae to mature adults, was conducted by means of integrative microscopy techniques, i.e., light, electron, and confocal microscopy.
  
  
  RESULTS
  Initially unfolded, the pallial margin is divided into distal and proximal regions by the periostracum-forming zone. The emergence of the pallial musculature and its neural innervation are crucial steps during bivalve larval development. By the late pediveliger stage, the margin becomes folded, resulting in a bilobed condition (i.e., outer and inner folds), a periostracal groove, and the development of different types of cilia. After metamorphosis, a second outgrowth process is responsible for emergence of the middle mantle fold from the outer surface of the inner fold. Once the three-folded condition is established, the general adult features are rapidly formed.
  
  
  CONCLUSIONS
  Our data show that the middle mantle fold forms from the outer surface of the inner fold after metamorphosis and that the initial unfolded mantle margin may represent a common condition among bivalves. The first outgrowth process, which gives rise to the outer and inner folds, and the emergence of the pallial musculature and innervation occur during larval stages, highlighting the importance of the larval period for mantle margin morphogenesis in Bivalvia.
authors.affiliation: Department of Zoology, University of São Paulo, Rua do Matão, Travessa 14, n. 101, 05508-090, São Paulo, SP, Brazil. jorgeaudino@ib.usp.br.
authors.forename: Jorge A
authors.initials: JA
authors.lastname: Audino
authors.affiliation: Department of Zoology, University of São Paulo, Rua do Matão, Travessa 14, n. 101, 05508-090, São Paulo, SP, Brazil. jemarian@ib.usp.br.
authors.forename: José Eduardo A R
authors.initials: JE
authors.lastname: Marian
authors.affiliation: Department of Integrative Zoology, University of Vienna, UZA1 Althanstraße 14, 1090, Vienna, Austria. andreas.wanninger@univie.ac.at.
authors.forename: Andreas
authors.initials: A
authors.lastname: Wanninger
authors.affiliation: Department of Zoology, University of São Paulo, Rua do Matão, Travessa 14, n. 101, 05508-090, São Paulo, SP, Brazil. sonialop@ib.usp.br.
authors.forename: Sônia G B C
authors.initials: SG
authors.lastname: Lopes
mesh_terms: D000818:Animals; D007814:Larva / Q000254:growth & development; D008974:Mollusca / Q000254:growth & development*; D009024:Morphogenesis