Ultrastructure of the postcorpus of the esophagus of Teratocephalus lirellus (Teratocephalida) and its use for interpreting character evolution in Secernentea (Nematoda)

Abstract

The ultrastructure of the postcorpus of the putative outgroup of Secernentea (Nematoda), Teratocephalus lirellus (Teratocephalida), is compared with previous observations of representative species Zeldia punctata (Cephalobina), Caenorhabditis elegans (Rhabditina), and Diplenteron sp. (Diplogastrina) in order to interpret the evolution of feeding structures within Secernentea. The postcorpus of T. lirellus consists of 6 marginal, 13 muscle, 3 gland, and 11 nerve cells. In both T. lirellus and Z. punctata, one duct from each of two subventral glands opens into the esophageal lumen at the junction of the isthmus and the basal bulb, whereas in C. elegans and Diplenteron sp., homologous openings are at the posterior end of the median bulb. Caenorhabditis elegans and Z. punctata each have two additional glands that open within the basal bulb. The postcorpus of each taxon has four anterior-to-posterior layered sets of radial muscle cells, except in Diplenteron sp., which lacks a grinder and has homologs to the anterior two sets only. The anterior set of muscles of T. lirellus and Z. punctata includes six mononucleate cells, whereas the homolog in C. elegans and Diplenteron sp. includes three binucleate cells. Evaluation of character polarity defines Rhabditina and Diplogastrina as sister taxa, and suggests that the character of five glands may result from functional convergence.

Fine structure and phylogenetic significance of a muscular basal bulb in Basiria gracilis Thorne, 1969 (Nematoda: Tylenchidae)

“…The ultrastructure of the basal bulb has been examined in representatives of a number of orders of Secernentea (Albertson & Thomson, 1976;Zhang & Baldwin, 1999, 2000, 2001. This provides a basis for comparison with Tylenchida where the region may be a basal bulb or derived as intestine-overlapping glands.…”

“…These classical evolutionary schemes have been challenged by new data including character sets from molecular biology, early embryogenesis, and detailed comparative morphology (Baldwin et al, 1997;Fitch, 1997;Blaxter et al, 1998;Dolinski et al, 1998Dolinski et al, , 2001Zhang & Baldwin, 1999, 2000, 2001. More speci cally, recent ndings are inconsistent with the classical hypothesis that diplogastrids and tylenchids are sister taxa, and call for a reevaluation of the classical interpretation of the nonmuscular glandular basal bulb, lacking a valve or pump, as a synapomorphy that unites diplogastrids and tylenchids.…”

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

“…Usually, close relatives of the group of interest are selected as outgroup species. We chose T. lirellus because of its close relation to the free-living soil nematodes (Blaxter et al, 1998), and also because T. lirellus had previously been used as an outgroup to the free-living soil nematodes (Zhang and Baldwin, 2001). …”

Three‐dimensional reconstruction of the nose epidermal cells in the microbial feeding nematode, Acrobeles complexus (Nematoda: Rhabditida)

“…It is noteworthy that the two taxa, although not closely related, share many ancestral attributes in their feeding morphologies (Van de Velde et al, 1994;Dolinski et al, 1998;Zhang and Baldwin, 2001). The cuticle of the nose region in the Cephalobina can be modified into elaborate appendages, probolae ( Fig.…”