Ultrastructure and function of the pharynx of Gnathostomula paradoxa (Gnathostomulida)

Abstract

The pharynx of Gnathostomula paradoxa consists of the partly syncytial pharyngeal musculature, a pharyngeal epithelium, myoepitheliocytes, receptors, nerves, and three solid parts, called the jugum, the basal plate, and the jaw. Extended non-contractile regions of both pharyngeal and body wall musculature form the socalled parenchymatous tissue between the digestive tract and the body wall. The pharyngeal epithelium mediates the force from the pharyngeal musculature to the solid parts. The basal plate and jaw contain longitudinal cuticular rods which are elastic antagonists of the musculature. There is no buccal ganglion in G. paradoxa. The study supports the monophyly of the Gnathostomulida and Gnathifera.& b d y :

New characters in the Gnathostomulid mouth parts revealed by scanning electron microscopy

“…10A) and seem to represent an intermediate state between the swollen and the fibrillate form. The rods have also been described in investigations based on TEM (Lammert, 1986;Herlyn and Ehlers, 1997), and their ultrastructure is rather constant within Gnathostomulida. In TEM, transverse sections of the rods appear as translucent structures with an electron-dense core (Lammert, 1986;Rieger and Tyler, 1995;Herlyn and Ehlers, 1997).…”

“…The rods have also been described in investigations based on TEM (Lammert, 1986;Herlyn and Ehlers, 1997), and their ultrastructure is rather constant within Gnathostomulida. In TEM, transverse sections of the rods appear as translucent structures with an electron-dense core (Lammert, 1986;Rieger and Tyler, 1995;Herlyn and Ehlers, 1997). Since all articularia investigated in both Filospermoidea and Bursovaginoidea are made up of lamellar rods, this trait can be considered a characteristic of gnathostomulid jaws.…”

“…Also, its function remains equally uncertain. Riedl and Rieger (1972) suggested that it serves as a muscle attachment site but more recent studies have shown that it does not contain muscular tissue (Herlyn and Ehlers, 1997;Tyler and Hooge, 2001).…”

“…About 95 species in 25 genera are currently known worldwide (Sterrer, 1998), predominantly from the North Sea, the Mediterranean, the Caribbean, and the South Pacific. Molecular and morphological evidence (Rieger and Tyler, 1995;Herlyn and Ehlers, 1997;Giribet et al, 2000;Sørensen et al, 2000) points to a close relationship between Gnathostomulida, Rotifera, Acanthocephala, and the recently described Micrognathozoa (Kristensen and Funch, 2000).…”

A modern approach to rotiferan phylogeny: Combining morphological and molecular data

“…Inner budding does not occur in any other taxa included in this analysis. The character refers to the presence of pharyngeal hard parts composed of longitudinally arranged rods with a conspicuous ultrastructure (see Ahlrichs, 1995a;Rieger and Tyler, 1995;Herlyn and Ehlers, 1997;Kristensen and Funch, 2000). Such jaws are present only in Gnathostomulida, Micrognathozoa, and Rotifera (but not in Acanthocephala).…”