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Nilonema gymnarchi Khalil, 1960 and N. senticosum (Baylis, 1922) (Nematoda: Dracunculoidea): Gondwana relicts?

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Data-base searches of records of the helminth parasites of South American and African freshwater fishes revealed only two pairs of species from genera endemic to the two regions. One pair, species of the primitive amphilinid cestode genus Nesolecithus Dönges & Harder, 1966, has already been designated as likely Gondwana relicts. The second pair are the philometrid nematodes Nilonema gymnarchi Khalil, 1960 from Gymnarchus niloticus Cuvier (Gymnarchidae) in Africa and N. senticosum (Baylis, 1922) from the South American fish Arapaima gigas (Cuvier) (Arapaimidae). Both species are partly redescribed on the basis of light and scanning electron microscopical observations of the type-specimens, and their relationships are discussed. In view of the fact that both hosts are basal teleosts of the order Osteoglossiformes and they are the same two fish which harbour the amphilinid cestodes already indicated as Gondwana relics, the nematode pair is also deemed to be relictual. However, these species are suggested as being of limited potential value for calibrating a molecular clock.

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We are grateful to the Brazilian Academy of Sciences and The Royal Society of London for financial support, which enabled the senior author to visit the Natural History Museum (NHM) in London. We are grateful to Dr Alex Ball, NHM, for access to the SEM facilities, Dr Martha Richter, NHM, for bibliographic support and Drs Pavel Nikolov and Bokyo Georgiev, BAS, for Russian translations.

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Correspondence to Cláudia Portes Santos.

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Santos, C.P., Gibson, D.I. Nilonema gymnarchi Khalil, 1960 and N. senticosum (Baylis, 1922) (Nematoda: Dracunculoidea): Gondwana relicts?. Syst Parasitol 67, 225–234 (2007). https://doi.org/10.1007/s11230-006-9080-4

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  • Scanning Electron Microscopy Observation
  • Helminth Parasite
  • Anterior Extremity
  • South American Species
  • Helminth Fauna