- Tachycines Adelung 1902
- Tachypleus Leach 1819
- Tachysurus Lacépède 1803
- Tachyura Motschulsky 1862
- Taenia Linnaeus 1758
- Taeniastrotos Cressey 1969
- Taenioides Lacépède 1800
- Taeniothrips Amyot & Serville 1843
- Taimenobdella Epshtein 1987
- Takemasaia Azuma & Minato 1976
- Takifugu Abe 1949
- Tamarix
- Tamias Illiger 1811
- Tamoya F. Müller 1859
- Tanakia D.S. Jordan & W.F. Thompson 1914
- Tanakius Hubbs 1918
- Tapes Megerle von Mühlfeld 1811
- Tapinoma Förster 1850
- Taraxacum F.H. Wiggers
- Tarebia H. Adams & A. Adams 1854
- Tarenna J. Gaertner 1788
- Taricha Gray 1950
- Tarphops D.S. Jordan & W.F. Thompson 1914
- Tarsiger Hodgson 1845
- Taxonus Hartig 1837
- Technomyrmex Mayr 1872
- Tectus Montfort 1810
- Tegulorhynchia Chapman & Crespin 1923
- Telorchis Lühe 1899
- Temnopleurus L. Agassiz 1841
- Temnothorax Mayr 1861
- Temnotrema A. Agassiz 1863
- Tenebrio Linnaeus 1758
- Tenguella Arakawa 1965
- Tenodera Burmeister 1838
- Tenthredo Linnaeus 1758
- Tenthredopsis O. Costa 1859
- Terapon Cuvier 1817
- Teratocoris Fieber 1858
- Terebella Linnaeus 1767
- Terebratalia Beecher 1893
- Terebratella d'Orbigny 1847
- Terebratula Müller 1776
- Terebratulina d'Orbigny 1847
- Terpsiphone Gloger 1827
- Testudinella Bory de St. Vincent 1826
- Tetraclita Schumacher 1817
- Tetraclitella Hiro 1939
- Tetracotyle Fillipi 1859
- Tetragomphius Baylis & Daubney 1923
- Tetrameres Creplin 1846
- Tetramorium Mayr 1855
- Tetraonchus Diesing 1858
- Tetrapocillon Brøndsted 1924
- Tetraponera Smith 1852
- Tetrastemma Ehrenberg 1831
- Tetrosomus Swainson 1839
- Thais Röding 1798
- Thalamita Latreille 1829
- Thalassoma Swainson 1839
- Thalictrum
- Thamnaconus Smith 1949
- Thamnomys Thomas 1907
- Thaumastochiton Thiele 1909
- Thalessa H. Adams & A. Adams 1853
- Thecidellina Thomson 1915
- Thecocodium Bouillon 1967
- Thelazia Bosc in Blainville 1819
- Thelenota Brandt 1835
- Thelepus Leuckart 1849
- Theora H. Adams & A. Adams 1856
- Theragra Lucas 1898
- Thermocyclops Kiefer 1927
- Thermopsis
- Thersitina Norman 1905
- Thominx Dujardin 1845
- Thrips Linnaeus 1758
- Thromidia Pope & Rowe 1977
- Thuidium
- Thujopsis von Siebold & Zuccarini ex Endlicher
- Thunnus South 1845
- Thyreus Panzer 1806
- Thysanophrys Ogilby 1898
- Tiarinia Dana 1851
- Tichosina Cooper 1977
- Tilapia Smith 1840
- Timarete Kinberg 1866
- Timorichthys J.G.Nielsen & Schwarzhans 2011
- Tinginotopsis Poppius 1915
- Tinginotum Kirkaldy 1902
- Tjalfiella Mortensen 1910
- Todarodes Steenstrup 1880
- Tokudaia Kuroda 1943
- Tomiyamichthys Smith 1956
- Tonicella Carpenter 1873
- Torquigener Whitley 1930
- Torreya G.A. Walker-Arnott
- Torynurus Baylis & Daubney 1925
- Totta Ghauri & Ghauri 1983
- Toxascaris Leiper 1907
- Toxeuma Walker 1833
- Toxicodendron Miller
- Toxocara Stiles & Hassal 1905
- Toxopneustes L. Agassiz 1841
- Trachelobdella Diesing 1850
- Trachidermus Heckel 1837
- Trachinocephalus Gill 1861
- Trachinotus Lacépède 1801
- Trachemys Agassiz 1857
- Trachurus Rafinesque 1810
- Transversotrema Witenberg 1944
- Trapa Linné
- Trechiama Jeannel 1927
- Trechus Clairville 1806
- Trema Loureiro
- Trephionus Bates 1883
- Trevathana Anderson 1992
- Triacanthus Oken 1817
- Triakis J.P. Müller & Henle 1838
- Trialeurodes Cockerell 1902
- Trianguloscalpellum Zevina 1978
- Triarthron Märkel 1840
- Tribolodon Sauvage 1883
- Trichinella Railliet 1895
- Trichiurus Linnaeus 1758
- Trichocephalus Schrank 1788
- Trichocerca Lamarck 1801
- Trichodina Ehrenberg 1831
- Tricholinstowia Travassos 1937
- Trichonotus Bloch & Schneider 1801
- Trichosomoides Raillet 1895
- Trichostrongylus Looss 1905
- Trichotichnus A. Morawitz 1863
- Trichotria Bory De St. Vincent 1827
- Trichuris Roederer 1761
- Tridacna Bruguière 1797
- Tridentiger T.N. Gill 1859
- Trigomphus Bartenev 1911
- Trigonognatha Motschulsky 1858
- Trigonotoma Dejean 1828
- Triliropus Mayer 1903
- Trimeresurus Lacépède 1804
- Trimma Jordan & Saele 1906
- Triodontophorus Looss 1902
- Triperopus Mayer 1903
- Triprotella Arimoto 1970
- Trishoplita Jacobi 1898
- Triso Randall, Johnson & Lowe 1989
- Tristramella Trewavas 1942
- Tritodynamia Ortmann 1894
- Trochicola Dollfus 1914
- Trochochlamys Habe 1946
- Troglodytes Vieillot 1809
- Trogonoptera Rippon 1890
- Troides Hübner 1819
- Tromikosoma Mortensen 1903
- Tropiometra A.H. Clark 1907
- Tropocyclops Kiefer 1927
- Trychosis Förster 1869
- Trypanosyllis Claparède 1864
- Trypoxylon Latreille 1796
- Trypoxylus Minck 1920
- Tscherskia Ognev 1914
- Tubastraea Lesson 1829
- Tupiocoris China & Carvalho 1952
- Turbinaria J.V. Lamouroux 1825
- Turbo Linnaeus 1758
- Turdus Linnaeus 1758
- Turrilatirus Vermeij & M. A. Snyder 2006
- Turritopsis McCrady 1857
- Tursiops Gervais 1855
- Turtonia Alder 1848
- Tylosurus Cocco 1833
- Typha Linné
- Typhlotriton Andersson 1871
- Typosyllis Langerhans 1879
- Tyrannophaedusa Pilsbry 1901