Abstract
BackgroundMyogenesis is currently investigated in a number of invertebrate taxa using combined techniques, including fluorescence labeling, confocal microscopy, and 3D imaging, in order to understand anatomical and functional issues and to contribute to evolutionary questions. Although developmental studies on the gross morphology of bivalves have been extensively pursued, organogenesis including muscle development has been scarcely investigated so far.ResultsThe present study describes in detail myogenesis in the scallop Nodipecten nodosus (Linnaeus, 1758) during larval and postmetamorphic stages by means of light, electron, and confocal microscopy. The veliger muscle system consists of an anterior adductor muscle, as well as four branched pairs of striated velum retractors and two pairs of striated ventral larval retractors. The pediveliger stage exhibits a considerably elaborated musculature comprising the velum retractors, the future adult foot retractor, mantle (pallial) muscles, and the anterior and posterior adductors, both composed of smooth and striated portions. During metamorphosis, all larval retractors together with the anterior adductor degenerate, resulting in the adult monomyarian condition, whereby the posterior adductor retains both myofiber types. Three muscle groups, i.e., the posterior adductor, foot retractor, and pallial muscles, have their origin prior to metamorphosis and are subsequently remodeled.ConclusionsOur data suggest a dimyarian condition (i.e., the presence of an anterior and a posterior adductor in the adult) as the basal condition for pectinids. Comparative analysis of myogenesis across Bivalvia strongly argues for ontogenetic and evolutionary independence of larval retractors from the adult musculature, as well as a complex set of larval retractor muscles in the last common bivalve ancestor.Electronic supplementary materialThe online version of this article (doi:10.1186/s12983-015-0125-x) contains supplementary material, which is available to authorized users.
Highlights
Myogenesis is currently investigated in a number of invertebrate taxa using combined techniques, including fluorescence labeling, confocal microscopy, and 3D imaging, in order to understand anatomical and functional issues and to contribute to evolutionary questions
To inject novel data into the discussion of shared and diverging morphological characters within Pectinidae and across Bivalvia, and to reconstruct potential bivalve larval ground patterns, the present study provides a detailed description of myogenesis in the scallop Nodipecten nodosus (Linnaeus, 1758) during larval and postmetamorphic development
A prototroch muscle ring is present in bivalves [19, 31], gastropods [11, 13], polyplacophorans [15], and aplacophorans [16, 53], and appears to be a feature of the larval muscular architecture of the last common molluscan ancestor [10]
Summary
Myogenesis is currently investigated in a number of invertebrate taxa using combined techniques, including fluorescence labeling, confocal microscopy, and 3D imaging, in order to understand anatomical and functional issues and to contribute to evolutionary questions. Ontogeny of bivalve gross anatomy has been widely investigated during the past two centuries and bivalve larvae have been used as models in studies dealing with diverse biological questions (e.g., [1, 2]) Developmental studies in this class-level taxon of mollusks have been performed for numerous species using light and electron microscopy, and a large bulk of data on larval general morphology is available (e.g., [3, 4]). Modern methods including fluorescence staining combined with confocal microscopy and three-dimensional reconstruction have been successfully applied in the last decade to study invertebrate organogenesis, including muscular development (see [9, 10] for reviews). Such techniques, phalloidin staining, represent a powerful tool for studies
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