Species (22.489)
- Undella bulla Kofoid & Campbell 1929
- Undella atenuata Jörgensen 1924
- Undella californiensis Kofoid & Campbell 1929
- Undella claparedei Entz 1885
- Undella clevei Jörgensen 1924
- Undella declivis Kofoid & Campbell 1929
- Undella dohrnii Daday 1887
- Urceolaria elongata Fenchel 1965
- Urceolaria heraldica Jankowski 1974
- Urceolaria karyodactyla Laird 1961
- Urceolaria korschelti Zick 1928
- Urceolaria patellae Cuenot 1891
- Urceolaria paradoxa Claparède & Lachmann 1858
- Urceolaria spinicola Beers 1964
- Urceolaria synaptae Cuenot 1890
- Urliella terricola Foissner 1989
- Urocentrum trichocystus Smith 1897
- Urnulella costata Szczechura 1969
- Urochaenia ichthyoides Savi 1913
- Urocyclon chesapeakensis Small & Lynn 1985
- Urocyclon filificus Kahl 1931
- Uroleptoides qingdaoensis Song & Wilbert 1989
- Uroleptopsis citrina Kahl 1932
- Uroleptopsis multiseta Dragesco 1970
- Uroleptopsis viridis Perejaslawzewa 1886
- Uroleptopsis ovata Horvath 1933
- Uroleptopsis roscoviana Maupas 1983
- Uroleptus americanus Calkins 1919
- Uroleptus longicaudatus Stokes 1886
- Uroleptus mobilis Engelmann 1862
- Uroleptus musculus Müller 1786
- Uroleptus muscorum Kahl 1932
- Uroleptus notabilis Foissner 1982
- Uroleptus natronophilus Dietz 1965
- Uroleptus novitas Horvath 1933
- Uroleptus opisthobolus Stokes 1886
- Uroleptus sphagni Stokes 1886
- Uroleptus violaceus Stein 1859
- Uronema acutum Buddenbrock 1920
- Uronema antarcticum Thompson 1972
- Uronema biceps Penard 1922
- Uronema caudatum Martini 1910
- Uronema constantzianum Tucolesco 1962
- Uronema dubium Penard 1922
- Uronema mirum Penard 1922
- Uronema nigricans Müller 1786
- Uronychia setigera Calkins 1902
- Uronychia uncinata Taylor 1927
- Uropedalium antarcticum Thompson 1972
- Uropedalium pyriforme Kahl 1928
- Urosoma acuminata Stokes 1887
- Uropedalium opisthostomum Lepsi 1926
- Urosoma caudata Stokes 1887
- Urosoma ambigua Dragesco & Dragesco-Kernéis 1986
- Urosoma cienkowski Kowalewski 1882
- Urosoma cienkowskii Kowalewski 1882
- Urosoma gigantea Horváth 1933
- Urosoma longicirrata Kahl 1932
- Urosoma karinae Foissner 1987
- Urosoma macrostyla Wrzesniowski 1870
- Urosoma octonucleata Berger & Foissner 1989
- Urosoma planctonicum sensu Wilbert 1969
- Urosomoida agiliformis Foissner 1982
- Urosomoida agilis Engelmann 1862
- Urosomoida dorsiincisura Foissner 1982
- Urosomoida antarctica Foissner 1996
- Urosomoida minima Hemberger 1985
- Urosomoida n.sp.
- Urosomoida granulifera Foissner 1996
- Urosomoida perthensis Foissner & O'Donoghue 1990
- Urospina bicaudata Gelei 1944
- Urostrongylum caudatum Kahl 1932
- Undella dilatata Kofoid & Campbell 1929
- Undella hemispherica Laackmann 1909
- Undella lachmanni Daday 1887
- Undella hyalinella Kofoid & Campbell 1929
- Undella ostenfeldi Kofoid & Campbell 1929
- Undella parva Kofoid & Campbell 1929
- Undella peruana Kofoid & Campbell 1929
- Undella pistillum Kofoid & Campbell 1929
- Undella pusilla Paulsen 1904
- Undellopsis bicollaria Kofoid & Campbell 1929
- Undella turgida Kofoid & Campbell 1929
- Urocentrum turbo Müller 1786
- Urocyclon filificum Small & Lynn 1985
- Uroleptoides atypicus Hemberger 1985
- Uroleptoides binucleatus Hemberger 1985
- Uroleptoides caudatus Hemberger 1985
- Uroleptoides kihni Wenzel 1953
- Uroleptoides vitiphilus Foissner 1987
- Uroleptoides quadrinucleatus Foissner 1984
- Urospinula bicaudata Corliss 1960
- Urostrongylum contortum Kahl 1932
- Urostyla brachytona Stokes 1886
- Urostyla caudata Stokes 1886
- Urostyla chlorelligera Foissner 1980
- Urostyla concha Entz 1884
- Urostyla dispar Kahl 1932
- Urostyla elongata Stokes 1891
- Urostyla flavicans Wresniowski 1870