Observations on the systematics of the genus Difflugia in Britain (Rhizopoda, Protozoa). F GENERAL 28 JANW83 ^4L Colin G. Ogden Department of Zoology, British Museum (Natural History), Cromwell Road, London SW7 5BD Contents Synopsis Introduction Materials and methods Systematic descriptions Pyriform and elongate species . . . . Pointed species or those with protruberances . Ovoid or spherical species Compressed species Discussion References Index . 1 1 2 2 2 27 45 59 66 69 73 Synopsis Detailed descriptions of the shell structure in thirty-eight species of Difflugia are given, and further information on one species which has been redescribed in an earlier report (Ogden & Fairman, 1979) is included. Two new species, Difflugia hiraethogii and D. stoutii, are described, and other systematic changes include the following new combinations: D. cylindrus (Thomas, 1953), D. lacustris (Penard, 1899), D. microclaviformis (Kourov, 1925), D. microstoma (Thomas, 1954), D. parva (Thomas, 1954), D. tennis (Penard, 1890), D. tricornis (Jung, 1936), D. venusta (Penard, 1902) and D. distenda nom, nov., D. gassowskii nom, nov., D. paulii nom. nov., D. rotunda nom. nov. Seventeen of these redescriptions are new records for the British Isles. The structure of the shell is discussed and the patterning of the organic cement which binds the particles together is shown to be a useful taxonomic character. Introduction The taxonomy of specimens belonging to the genus Difflugia is based mainly on differences in size and shape of the agglutinated shells constructed by these animals. Comparison of cytoplasmic features are either difficult or impossible because most of it is encased by the shell which is often opaque. Differences in the shell features have resulted in about three hundred named species, varieties and forms being currently attributed to the genus. This proliferation of species is due to a combination of the lack of good diagnostic features and inadequate descriptions. The problem is clearly shown in the only comprehensive survey of the genus, based on African specimens, by Gauthier-Lievre and Thomas (1958). In this work the authors had difficulties with several groups of individuals which shared common features, and as a result, about half of the 129 species described were designated as varieties or forms. Some earlier studies (Ogden, 1979, 1980; Ogden & Fairman, 1979) were con-cerned with the variation of specimens having a pyriform shell, and the surface Bull. Br. Mus. nat. Hist. (Zool.)44 (1): 1-73 Issued 2 7 January 1983
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