We review the species of Difflugia with a shell that is pyriform or elongate, based primarily on examinations of two collections in the Natural History Museum, London, UK: (i) Penard’s collection of balsam-mounted microscope slides, and (ii) Ogden’s scanning electron micrographs and shell measurements. We discuss taxa grouped into seven species complexes, namely Difflugia oblonga Ehrenberg, 1838, Difflugia pyriformis Perty, 1849, Difflugia bryophila (Penard, 1902) Jung, 1942, Difflugia linearis (Penard, 1890) Gautier-Lièvre et Thomas, 1958, Difflugia gigantea (Chardez, 1967) Ogden et Fairman, 1979, Difflugia petricola Cash, 1909, and Difflugia lanceolata Penard, 1890. Within the D. oblonga-complex we: (i) distinguish as a separate taxon the typical form of D. oblonga Ehrenberg, 1838; (ii) synonymise D. parva (Thomas, 1954) Ogden, 1983, D. lacustris (Penard, 1899) Ogden, 1983, D. bacillifera Penard, 1890, D. oblonga var. incondita Gauthier-Lièvre et Thomas, 1958, and D. oblonga f. cyphodera Jung, 1942 with D. oblonga. Within the D. pyriformis-complex we: (i) distinguish as separate taxa the typical form of D. pyriformis Perty, 1849, as well as D. capreolata Penard, 1902, and (ii) synonymise D. cylindrus (Thomas, 1953) Ogden, 1983 with D. pyriformis Perty, 1849. Within the D. bryophila-complex we: (i) distinguish as a separate taxon D. bryophila (Penard, 1902) Jung, 1942, and (ii) synonymise D. gassowskii (Gassowsky, 1936) Ogden, 1983 with D. bryophila. Within the D. linearis-complex we: (i) distinguish as a separate taxon D. linearis (Penard, 1890) Gautier-Lièvre et Thomas, 1958, and (ii) synonymise D. paulii Ogden, 1983 and D. nebeloïdes Gauthier-Lièvre and Thomas, 1958 with D. linearis. Within the D. gigantea-complex we: (i) distinguish as a separate taxon the typical form of D. gigantea (Chardez, 1967) Ogden et Fairman, 1979, and (ii) discuss the validity of D. oblonga var. angusticollis Štěpánek, 1952, and D. oblonga var. stepaneki (Štěpánek, 1952) Decloitre. Within the D. petricola-complex we accept D. petricola Cash, 1909 as a valid species and suggest its possible relationships with other Difflugia species. Within the D. lanceolata-complex we accept D. lanceolata Penard, 1890 as a valid species and illustrate its variability based on C.G. Ogden’s SEM micrographs. As in the first part of this series of papers in which we taxonomically revise the genus Difflugia we conclude that, based on current knowledge, it is unclear whether these species complexes represent single, highly polymorphic species, or groups of sibling species. Further studies based on a combination of morphometric, ultrastructural (SEM), molecular, and environmental data are needed in order to characterize these species complexes in more detail and thus resolve their systematics.
Protistology
2014. — Выпуск 4
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