title: Developmental dynamics of myogenesis in the shipworm Lyrodus pedicellatus (Mollusca: Bivalvia).
abstract: BACKGROUND
  The shipworm Lyrodus pedicellatus is a wood-boring bivalve with an unusual vermiform body. Although its larvae are brooded, they retain the general appearance of a typical bivalve veliger-type larva. Here, we describe myogenesis of L. pedicellatus revealed by filamentous actin labelling and discuss the data in a comparative framework in order to test for homologous structures that might be part of the bivalve (larval) muscular ground pattern.
  
  
  RESULTS
  Five major muscle systems were identified: a velum retractor, foot retractor, larval retractor, a distinct mantle musculature and an adductor system. For a short period of larval life, an additional ventral larval retractor is present. Early in development, a velum muscle ring and an oral velum musculature emerge. In late stages the lateral and dorsal mantle musculature, paired finger-shaped muscles, an accessory adductor and a pedal plexus are formed. Similar to other bivalve larvae, L. pedicellatus exhibits three velum retractor muscles, but in contrast to other species, one of them disappears in early stages of L. pedicellatus. The remaining two velum retractors are considerably remodelled during late larval development and are most likely incorporated into the elaborate mantle musculature of the adult.
  
  
  CONCLUSIONS
  To our knowledge, this is the first account of any larval retractor system that might contribute to the adult bodyplan of a (conchiferan) mollusk. A comparative analysis shows that a pedal plexus, adductors, a larval velum ring, velum retractors and a ventral larval retractor are commonly found among bivalve larvae, and thus most likely belong to the ground pattern of the bivalve larval musculature.
authors.affiliation: Department of Integrative Zoology, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria.
authors.forename: Andrea
authors.initials: A
authors.lastname: Wurzinger-Mayer
authors.affiliation: Institute of Marine Sciences, University of Portsmouth, Ferry Road, Portsmouth, P04 9LY UK.
authors.forename: J Reuben
authors.initials: JR
authors.lastname: Shipway
authors.affiliation: Department of Integrative Zoology, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria.
authors.forename: Alen
authors.initials: A
authors.lastname: Kristof
authors.affiliation: Department of Integrative Zoology, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Schwaha
authors.affiliation: Institute of Marine Sciences, University of Portsmouth, Ferry Road, Portsmouth, P04 9LY UK.
authors.forename: Simon M
authors.initials: SM
authors.lastname: Cragg
authors.affiliation: Department of Integrative Zoology, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria.
authors.forename: Andreas
authors.initials: A
authors.lastname: Wanninger
keywords: Evodevo; Evolution; Larva; Lophotrochozoa; Mollusk; Ontogeny; Teredinid; Veliger