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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 6671

Ralph O. Brinkhurst; Lumbriculids, branchiobdellidans and leeches: an overview of recent progress in phylogenetic research on clitellates. Hydrobiologia 406:281-290, 1999

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The debates about the relationship among clitellate taxa at research conferences on aquatic oligochaetes have provided two alternative hypotheses. While both involve cladistic analyses, the differences focus on questions of homology. A single unique synapomorphy supports a taxon consisting of Branchiobdellida plus Lumbriculidae. Muscle ultrastructure provides a potential autapomophy for Lumbriculidae within the clade, while Branchiobdellida has many autapomophies. Some proposed synapomorphies for a Branchiobdellida plus Hirudinea grouping (jaws, oral sucker) are not based on homologous structures. Others (loss of chaetae, median male pore) are not unique, or are based on potentially convergent characters. Initial molecular analyses support a Branchiobdellida - Hiruadinea grouping. A preliminary manually drawn cladogram based on re-evaluted characters supports Lumbriculidae, Branchiobdellida, Acanthobdella and Euhirudinea as a monophyletic taxon. Observations on sperm ultrastructure support this hypothesis. If substantiated, a very considerable change in nomenclature well result. However, before any nomenclatural changes are proposed, a resolution of the apparently paraphyletic Oligochaeta is necessary.