Detailed reconstruction of the musculature in Limnognathia maerski (Micrognathozoa) and comparison with other Gnathifera.

Andreas Hejnol,Reinhardt M Kristensen,Katrine Worsaae,Nicolas Bekkouche,Martin V Sørensen

doi:10.1186/s12983-014-0071-z

Andreas Hejnol, Reinhardt M Kristensen + Show 3 more

Open Access

https://doi.org/10.1186/s12983-014-0071-z

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Abstract

IntroductionLimnognathia 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).ResultsThis 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.ConclusionsThe 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.

Highlights

Limnognathia maerski is the single species of the recently described taxon, Micrognathozoa
The musculature of the jaw apparatus shows several pairs of striated muscles largely related to the fibularium and the main jaws
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

Summary

Introduction

Limnognathia maerski is the single species of the recently described taxon, Micrognathozoa. Whereas the jaws of Limnognathia maerski previously have been subject to close examinations, the related musculature and other organ systems are far less studied. With a unique combination of characters, it is considered the only member of the Limnognathia maerski measures 80-150 μm, possesses a complex set of jaws, a conspicuously arranged ventral ciliation and, so far, only females are known. The overall musculature of L. maerski is briefly described. It is composed of several longitudinal and dorso-ventral muscles, minute muscles articulating the dorsal plates and a dense pharyngeal musculature. Ultrastructural data provided information on the structure of muscles attachment sites, the absence of myosyncytia and myoepithelia, the cross-striated nature of the pharyngeal musculature, and the mainly obliquely striated longitudinal musculature [3]

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