Scolex morphology of monozoic tapeworms (Caryophyllidea) from the Nearctic Region taxonomic and evolutionary implications

摘要

A comparative study of the scoleces of monozoic tapeworms (Cestoda: Caryophyllidea), parasites of catostomid and cyprinidfishes (Teleostei: Cypriniformes) in the Nearctic Region, was carried out using light and scanning electron microscopy. Scoleces of22 genera of North American caryophyllideans were characterised and their importance for taxonomy, classification and phylogeneticstudies was critically reviewed. Nearctic genera exhibit a much higher variation in the shape and form of scoleces compared with taxa inother biogeographical regions. The following basic scolex types can be recognised in Nearctic caryophyllideans: monobothriate (Pro-monobothrium Mackiewicz, 1968), loculotruncate (Promonobothrium, Dieffluvium Williams, 1978), bothrioloculodiscate (ArchigetesLeuckart, 1878, Janiszewskella Mackiewicz et Deutsch, 1976, Penarchigetes Mackiewicz, 1969, Pseudoglaridacris Oros, Uhrovi?et Scholz, 2018), fixomegabothriate (Capingens Hunter, 1927), bulbate and bulboacuminate (Atractolytocestus Anthony, 1958), cu-neiloculate (Hypocaryophyllaeus Hunter, 1927, Rowardleus Mackiewicz et Deutsch, 1976, Spartoides Hunter, 1929), biacetabulate,bulboloculate, bothrioloculodiscate (Biacetabulum Hunter, 1927), tholate (Hunterella Mackiewicz et McCrae, 1962), cuneifimbriate(Khawia Hsü, 1935), cuneiform (Calentinella Mackiewicz, 1974, Caryophyllaeides Nybelin, 1922, Edlintonia Mackiewicz, 1970),hastate (Pseudolytocestus Hunter, 1929), loculotholate (Bialovarium Fischthal, 1953, Pliovitellaria Fischthal, 1951), and cuneiformo-loculate (Glaridacris Cooper, 1920, Isoglaridacris Mackiewicz, 1965). The same type of scolex may be shared by species of differentgenera or families and species of the same genus can have a scolex of conspicuously different morphology, e.g. in Promonobothrium.Scolex morphology may be therefore of limited use in generic designation.