Comparative and functional morphology of the buccal cavity of Diplogastrina (Nematoda) and a first outline of the phylogeny of this taxon*

Abstract

The Diplogastrina include about 290 species of free living nematodes. Traditional classifications of this taxon are not based upon hypotheses of phylogenetic relationships. The highly variable structures of the buccal cavity were examined in 21 species using light microscopy and SEM. The function of the stomatal structures was studied with the aid of video recordings of living worms. The morphological data were used to reconstruct a first outline of the phylogenetic relationships of the Dipolgastrina. A rhabditoid gymnostomatal tube which is longer than wide, a short stegostom and a small dorsal tooth as in Pseudodiplogasteroides belong to the stem species pattern of Diplogastrina. Diplogastrina with a ‘Rhabditis’‐like gymnostomatal tube feed on bacteria and small fungal spores. A short and broad gymnostom as well as a right subventral tooth which forms a functional unit with the dorsal tooth were acquired step by step in the ancestral line leading to Mononchoides and Tylopharynx. The cuticularized cheilostom was divided into six plates connected by pliable regions twice independently within the Diplogastrina. The teeth‐bearing posterior part of the buccal capsule can move forewards by pushing apart the plates of the cheilostom so that the teeth can get in contact with food items that are too big to be sucked into the buccal cavity. Diplogastrina with a divided cheilostom can feed not only on bacteria, but also on larger fungal spores, ciliates or other nematodes. Tylopharynx is specialized to rip apart the cell wall of fungal hyphae with the movements of a dorsal and a subventral tooth in order to suck out the contents of the fungus. This shows that the transformation of the buccal cavity in Diplogastrina is linked with an expansion of ecological niches.

Evolutionary transformations of fetal membrane characters in Eutheria with special reference to Afrotheria

“…Accordingly, we reconstructed the stem species pattern or ancient condition of relevant taxa, such as Afrotheria, in order to discover transformations between subsequent nodes or stem species patterns. A stem species pattern is defined as the character set of the last common ancestor of a monophyletic taxon, including plesiomorphic and derived or apomorphic characters (Königs-mann, '75;Lieven and Sudhaus, 2000). For this purpose, the distribution of selected characters was mapped on a current hypothesis of phylogenetic relationships within Eutheria (see below).…”

Evolution of pharyngeal behaviors and neuronal functions in free-living soil nematodes

“…Additionally, to help determine the ancestral pattern of pharyngeal behaviors, we observed a close relative, Teratocephalus lirellus, as the outgroup species (Blaxter et al, 1998). Anatomically, the pharynxes in all of these species were similarly divided into the corpus, isthmus and terminal bulb (albeit with minor anatomical variations; see Chitwood and Chitwood, 1974;Maggenti, 1981;von Lieven, 2003;von Lieven and Sudhaus, 2000;Zhang and Baldwin, 1999). Yet behaviorally, each family, as well as T. lirellus, exhibited significant differences.…”

Simple methods for morphological observation of nematodes

“…Baldwin et al (1997) and Giblin-Davis et al (2006) employed transmission electron microscopy (TEM) to interpret the stomatal structure of Acrostichus halicti and Parasitodiplogaster larvigata. Light microscopy and a video-capture system were used to understand muscular movements and reconstruct complicated three-dimensional morphology of diplogastrids stoma (Fürst von Lieven and Sudhaus, 2000). Fürst von Lieven (2003) used 96% lactic acid to evert the buccal cavity of Oigolaimella spp., which made it easier to observe the various structures within it.…”