Bekkouche Nicolas, Kristensen Reinhardt M, Hejnol Andreas, Sørensen Martin V, Worsaae Katrine
Marine Biological Section, Department of Biology, University of Copenhagen, Universitetsparken 4, 2100 Copenhagen Ø, Denmark.
Natural History Museum of Denmark, Universitetsparken 15, 2100 Copenhagen Ø, Denmark.
Front Zool. 2014 Oct 1;11:71. doi: 10.1186/s12983-014-0071-z. eCollection 2014.
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).
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.
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.
马氏动颚虫是最近描述的分类单元微颚动物门中的唯一物种。这种动物最显著的特征是其复杂的颚部结构，类似于轮虫的咀嚼器和颚口线虫的颚部更为复杂的版本。尽管此前已经对马氏动颚虫的颚部进行了深入研究，但相关的肌肉组织和其他器官系统的研究却少得多。在此，我们利用共聚焦激光扫描显微镜对经鬼笔环肽染色的肌肉组织以及透射电子显微镜（TEM），对马氏动颚虫的身体和颚部肌肉组织进行了详细研究。
本研究揭示了一种复杂的体壁肌肉组织，包括六对主要的纵向肌肉和十三对躯干背腹肌肉。大多数纵向肌肉贯穿身体全长，一些纤维甚至分支并向前延伸至头部，向后延伸至腹部，形成复杂的肌肉组织。颚部器官的肌肉组织显示出几对横纹肌，主要与腓骨器和主要颚部相关。讨论了主要和次要肌肉对的颚关节和功能。未发现环形肌肉或肠道肌肉组织，但一些新发现的肌肉可能为肛门开口提供支持。
马氏动颚虫中纵向和背腹肌肉束呈松散网格状的组织方式，与轮虫中的组织方式更为相似，而非颚口线虫。尽管背腹肌肉组织可能与轮虫的环形肌肉不同源，但推测在身体伸展方面具有类似功能。此外，对马氏动颚虫、轮虫和颚口线虫的颚部肌肉组织进行功能比较，强调了腓骨器在马氏动颚虫中的重要作用，并表明其与轮虫的颚部组织在功能上更为相似。
