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

Abstract

Introduction: 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.

Insights into mud dragon morphology (Kinorhyncha, Allomalorhagida): myoanatomy and neuroanatomy of Dracoderes abei and Pycnophyes ilyocryptus

“…During the last decade, morphological studies of metazoans using modern techniques have started to cover a broader selection of animal groups, providing new insights into the diversification of organ systems (e.g., Bekkouche et al 2014;Bekkouche and Worsaae 2016;Gross and Mayer 2015;Kerbl et al 2015;Martin et al 2017). Some of these studies have focused on lesser-known taxa, such as the Scalidophora, which includes ecdysozoan groups with a radial head bearing scalids (Kinorhyncha, Loricifera and Priapulida) (Altenburger 2016;Herranz et al , 2014Herranz et al , 2019aMartín-Durán et al 2015;Neves et al 2013;Rothe and Schmidt-Rhaesa 2010).…”

A possible Cambrian stem-group gnathiferan-chaetognath from the Weeks Formation (Miaolingian) of Utah

“…Among the spiralians, the most fruitful comparisons may possibly lie with the Gnathifera. This monophyletic group (e.g., Laumer et al, 2015) comprises the gnathostomulids (e.g., Herlyn and Ehlers, 1997; Sørensen et al, 2006), its sister group the micrognathozoans (e.g., Bekkouche et al, 2014; Bekkouche and Worsaae, 2016), and the syndermatans (the group encompassing the rotifers and endoparasitic acanthocephalans; e.g., Rieger and Tyler, 1995; Sørensen, 2002a; Wulfken and Ahlrichs, 2012). Gnathiferans are millimetric and typically meiofaunal, but despite this, all possess intricate jaw apparatuses that reach an apogee in the complex array found in the micrognathozoans (e.g., Kristensen and Funch, 2000; De Smet, 2002; Sørensen, 2003).…”

Transitions in functional morphology from “large branchiopods” to Cladocera: Video and confocal microscopic studies of Cyclestheria hislopi (Cyclestherida) and Sida crystallina (Cladocera: Ctenopoda)

“…Some recent studies employed confocal laser scanning microscopy (CLSM) and F-actin staining of musculature on branchiopod trunk limbs (Kaji, Fritsch, Schwentner, Olesen, & Richter, 2014) and antennae (Maruzzo, Minelli, & Fusco, 2009). Factin staining in combination with 3D CLSM reconstructions has proven to be a useful technique for musculature reconstructions, especially for smaller muscle bundles and fibers of limbs and other structures, both in Arthropoda and many other invertebrates such as Annelida, Rotifera, and Gnathifera (e.g., Bekkouche, Kristensen, Hejnol, Sørensen, & Worsaae, 2014;Kerbl, Bekkouche, Sterrer, & Worsaae, 2015;Leasi, Neves, Worsaae, & Sørensen, 2012). Video techniques have previously been successfully used to describe arthropod limb motility, but only employed in a few studies of branchiopods (e.g., Olesen, 2005;Sigvardt & Olesen, 2014;Sigvardt, Rogers, & Olesen, 2017).…”