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

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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.

L'ultrastructure du post-corpus du groupe externe putatif des Secernentea (Nematoda), Teratocephalus lirellus (Teratocephalida), est comparé aux résultats d'observations antérieures de spécimens représentatifs de Zeldia punctata (Cephalobina), Caenorhabditis elegans (Rhabditina) et Diplenteron sp. (Diplogastrina) pour nous permettre d'interpréter l'évolution des structures reliées à l'alimentation chez les Secernentea. Le post-corpus de T. tirellus se compose de 6 cellules marginales, 13 cellules musculaires, 3 cellules glandulaires et 11 cellules nerveuses. Aussi bien chez Z. punctata que chez T. tirellus, l'un des canaux de chacune des glandes subventrales aboutit dans la lumière de l'oesophage à la jonction de l'isthme et du bulbe basal, alors que, chez C. elegans et Diplenteron sp., les ouvertures homologues sont à l'extrémité postérieure du bulbe médian. Caenorhabditis elegans et Z. punctata ont deux glandes additionnelles qui s'ouvrent dans le bulbe basal. Le post-corpus de chaque taxon possède quatre groupes de cellules musculaires radiales formant des couches de l'avant vers l'arrière, sauf Diplenteron sp. qui ne possède pas de broyeur et n'a que les homologues des deux groupes antérieurs de cellules. Le groupe antérieur de muscles de T. tirellus et Z. punctata compte six cellules mononucléées, alors que son homologue chez C. elegans et Diplenteron sp. contient trois cellules binucléées. L'évaluation de la polarité des caractères définit les Rhabditina et les Diplogastrina comme des taxons soeurs et semble indiquer que la répartition des cinq glandes résulte du phénomène de convergence fonctionnelle.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: January 1, 2001

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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