The tapeworm Archigetes sieboldi Leuckart, 1878 (Platyhelminthes: Cestoda: Caryophyllidea) has been cited as a likely representative of the “protocestode” condition, owing to its lack of segmentation and ability to attain sexual maturity in the invertebrate host (aquatic oligochaetes). The idea has been variously amplified or rejected in the literature, although the actual phylogenetic position of the species has not been investigated until now. New collections of Archigetes sp. from both its vertebrate and invertebrate hosts provided the opportunity to estimate its phylogenetic position with the use of molecular systematics, while prompting new analyses aimed at assessing the early diversification of the Cestoda. Additional collections representing the Amphilinidea, Caryophyllidea, and Gyrocotylidea were combined with published gene sequences to construct data sets of complete 18S (110 taxa) and partial (D1-D3) 28S (107 taxa) rDNA sequences, including 8 neodermatan outgroup taxa. Estimates resulting from Bayesian inference, maximum likelihood, and maximum parsimony analyses of the separate and combined data sets supported a derived position of the genus within the Caryophyllidea, and thus reject the idea that Archigetes sp. may exemplify a “primitive” condition. Topological constraint analyses rejected the hypothesis that Archigetes represents the most basal lineage of the Eucestoda, but did not rule out that it could represent the earliest branching taxon of the Caryophyllidea. In all analyses, the Eucestoda were monophyletic and supported basal positions of the nonsegmented Caryophyllidea and Spathebothriidea relative to other major lineages of the Eucestoda, implying that segmentation is a derived feature of the common ancestor of the di- and tetrafossate eucestodes. However, constraint analyses could not provide unequivocal evidence as to the precise branching patterns of the cestodarian, spathebothriidean, and caryophyllidean lineages. Phylogenetic analyses favor the interpretation that sexual maturity of Archigetes sp. in the invertebrate host, and similar examples in members of the Spathebothriidea, are the result of progenesis and have little if any bearing on understanding the protocestode condition.
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August 2008
Research Article|
August 01 2008
On the Position of Archigetes and Its Bearing on the Early Evolution of the Tapeworms
P. D. Olson;
P. D. Olson
Department of Zoology, The Natural History Museum, Cromwell Road, London SW7 5BD, U.K. P.Olson@nhm.ac.uk
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L. G. Poddubnaya;
L. G. Poddubnaya
Department of Zoology, The Natural History Museum, Cromwell Road, London SW7 5BD, U.K. P.Olson@nhm.ac.uk
* Institute of Biology of Inland Waters, Russian Academy of Sciences, 152742, Borok, Yaroslavl Province, Russia
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D. T J. Littlewood;
D. T J. Littlewood
Department of Zoology, The Natural History Museum, Cromwell Road, London SW7 5BD, U.K. P.Olson@nhm.ac.uk
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T. Scholz
T. Scholz
Department of Zoology, The Natural History Museum, Cromwell Road, London SW7 5BD, U.K. P.Olson@nhm.ac.uk
† Institute of Parasitology, Biology Centre of the Czech Academy of Sciences, Czech Republic, Branišovská 31, 370 05 České Budějovice, Czech Republic
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J Parasitol (2008) 94 (4): 898–904.
Citation
P. D. Olson, L. G. Poddubnaya, D. T J. Littlewood, T. Scholz; On the Position of Archigetes and Its Bearing on the Early Evolution of the Tapeworms. J Parasitol 1 August 2008; 94 (4): 898–904. doi: https://doi.org/10.1645/GE-1456.1
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