Af. Von Lieven et W. Sudhaus, Comparative and functional morphology of the buccal cavity of Diplogastrina (Nematoda) and a first outline of the phylogeny of this taxon, J ZOOL SYST, 38(1), 2000, pp. 37-63
Citations number
43
Categorie Soggetti
Animal Sciences
Journal title
JOURNAL OF ZOOLOGICAL SYSTEMATICS AND EVOLUTIONARY RESEARCH
The Diplogastrina include about 290 species of free living nematodes. Tradi
tional classifications of this taxon are not based upon hypotheses of phylo
genetic 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 li
ving worms. The morphological data were used to reconstruct a first outline
of the phylogenetic relationships of the Dipolgastrina. A rhabditoid gymno
stomatal tube which is longer than wide, a short stegostom and a small dors
al tooth as in Pseudodiplogasteroides belong to the stem species pattern of
Diplogastrina. Diplogastrina with a 'Rhabditis'-like gymnostomatal tube fe
ed 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 Mononchoi
des and Tylopharynx. The cuticularized cheilostom was divided into six plat
es connected by pliable regions twice independently within the Diplogastrin
a. The teeth-bearing posterior part of the buccal capsule can move foreward
s by pushing apart the plates of the cheilostom so that the teeth can get i
n contact with food items that are too big to be sucked into the buccal cav
ity. 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 moveme
nts 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 Dip
logastrina is linked with an expansion of ecological niches.