title: Detailed reconstruction of the musculature in Limnognathia maerski (Micrognathozoa) and comparison with other Gnathifera.
abstract: BACKGROUND
  Limnognathia maerski is the single species of the recently described taxon, Micrognathozoa. The most conspicuous character of this animal is the complex set of jaws, which resembles an even more intricate version of the trophi of Rotifera and the jaws of Gnathostomulida. Whereas the jaws of Limnognathia maerski previously have been subject to close examinations, the related musculature and other organ systems are far less studied. Here we provide a detailed study of the body and jaw musculature of Limnognathia maerski, employing confocal laser scanning microscopy of phalloidin stained musculature as well as transmission electron microscopy (TEM).
  
  
  RESULTS
  This study reveals a complex body wall musculature, comprising six pairs of main longitudinal muscles and 13 pairs of trunk dorso-ventral muscles. Most longitudinal muscles span the length of the body and some fibers even branch off and continue anteriorly into the head and posteriorly into the abdomen, forming a complex musculature. The musculature of the jaw apparatus shows several pairs of striated muscles largely related to the fibularium and the main jaws. The jaw articulation and function of major and minor muscle pairs are discussed. No circular muscles or intestinal musculature have been found, but some newly discovered muscles may supply the anal opening.
  
  
  CONCLUSIONS
  The organization in Limnognathia maerski of the longitudinal and dorso-ventral muscle bundles in a loose grid is more similar to the organization found in rotifers rather than gnathostomulids. Although the dorso-ventral musculature is probably not homologous to the circular muscles of rotifers, a similar function in body extension is suggested. Additionally, a functional comparison between the jaw musculature of Limnognathia maerski, Rotifera and Gnathostomulida, emphasizes the important role of the fibularium in Limnognathia maerski, and suggests a closer functional resemblance to the jaw organization in Rotifera.
authors.affiliation: Marine Biological Section, Department of Biology, University of Copenhagen, Universitetsparken 4, 2100 Copenhagen Ø, Denmark.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Bekkouche
authors.affiliation: Natural History Museum of Denmark, Universitetsparken 15, 2100 Copenhagen Ø, Denmark.
authors.forename: Reinhardt M
authors.initials: RM
authors.lastname: Kristensen
authors.affiliation: Sars International Centre for Marine Molecular Biology, University of Bergen, Thormøhlensgate 55, Bergen, N-5008 Norway.
authors.forename: Andreas
authors.initials: A
authors.lastname: Hejnol
authors.affiliation: Natural History Museum of Denmark, Øster Voldgade 5-7, 1350 Copenhagen K, Denmark.
authors.forename: Martin V
authors.initials: MV
authors.lastname: Sørensen
authors.affiliation: Marine Biological Section, Department of Biology, University of Copenhagen, Universitetsparken 4, 2100 Copenhagen Ø, Denmark.
authors.forename: Katrine
authors.initials: K
authors.lastname: Worsaae
keywords: 3D reconstructions; CLSM; F-actin; Jaw apparatus; Mastax; Trophi