Ta
- Taiaroa
- Taiaroidae
- Tamarisca
- Tamoya
- Tamoyidae
- Tanacetipathes
- Tasmanaria
- Tauroprimnoa
- Taxipathes
Te
- Tealia
- Tealianthus
- Tealidium
- Teclaia
- Teclaiidae
- Teissiera
- Teissieridae
- Telactinia
- Telesto
- Telestula
- Telmatactis
- Temnotrochus
- Tenuisis
- Tesserantha
- Tesseranthelia
- Tesseranthidae
- Tesserogastria
- Tethocyathus
- Tethrisis
- Tetracanna
- Tetracannoides
Tetrapathes Opresko, 2004
- Tetrapathes alata Brook, 1889
Cnidaria → Anthozoa → Antipatharia → Aphanipathidae → Aphanipathinae
Tetraplatia Busch, 1851
- Tetraplatia chuni Carlgren, 1909
- Tetraplatia volitans Busch, 1851
Cnidaria → Hydrozoa → Trachylinae → Narcomedusae → Tetraplatidae
- Tetraplatidae
- Tetraralphia
- Tetrorchis
Th
- Thalamophyllia
- Thalassianthidae
- Thalassianthus
- Thamnostoma
Thaumaptilon Conway Morris, 1993 †
- Thaumaptilon walcotti Conway Morris, 1993†
Cnidaria → Anthozoa → Pennatulacea
- Thecocodium
- Thecopsammia
- Thecoscyphus
- Thelogorgia
- Thermopalia
- Thesea
- Thoracactis
- Thouarella
- Thrombophyton
- Thrypticotrochus
- Thuiaria
- Thyroscyphidae
- Thyroscyphoides
- Thyroscyphus
- Thysanostoma
Ti
- Tiarannidae
- Tiaricodon
- Tiaropsidae
- Tiaropsidium
- Tiaropsis
- Tiburonia
Tima Eschscholtz, 1829
- Tima bairdii (Johnston, 1833)
- Tima flavilabris Eschscholtz, 1829
- Tima formosa L. Agassiz, 1862
- Tima saghalinensis Bigelow, 1913
Cnidaria → Hydrozoa → Hydroidolina → Leptothecata → Eirenidae
- Timoides
- Titanideum
Tj
†Tjanshanophyllum
Animalia → Cnidaria → Anthozoa → Rugosa
To
- Tobagogorgia
- Tokoprymno
- Toreuma
Tr
Podrazred Trachylinae Haeckel, 1879
- Actinulida Swedmark & Teissier, 1959
- Limnomedusae Kramp, 1938
- Narcomedusae Haeckel, 1879
- Trachymedusae Haeckel, 1866
Red Trachymedusae Haeckel, 1866
- Geryoniidae Eschscholtz, 1829
- Halicreatidae Fewkes, 1886
- Petasidae Haeckel, 1879
- Ptychogastriidae Mayer, 1910
- Rhopalonematidae Russell, 1953
Cnidaria → Hydrozoa → Trachylinae
Trachyphyllia Milne Edwards & Haime, 1849
- Trachyphyllia geoffroyi (Audouin, 1826)
Cnidaria → Anthozoa → Hexacorallia → Scleractinia → Merulinidae
- Trachyphylliidae
- Tregoubovia
- Trematocyathus
- Trematotrochus
- Triactis
- Triadopathes
- Trichactis
- Trichogorgia
- Trichydra
- Trichydridae
- Tricnidactis
- Tricyclusa
- Tricyclusidae
- Trimuricea
- Tripalea
- Tripedalia
- Tripoma
- Trissopathes
- Trochocyathus
- Trochopsammia
- Tropidocyathus
- Truncatoflabellum
- Truncatoguynia
Tu
- Tubastraea
- Tubiclavoides
- Tubiclavoididae
- Tubigorgia
- Tubipora
- Tubiporidae
- Tubularia
- Tubulariidae
- Turbinaria
- Turbinolia
- Turbinoliidae
- Turritopsis
- Turritopsoides
Ty
- Tylopathes