• Hydractinia Van Beneden, 1844
• Hydractinia (Euhydractinia) Broch, 1910 accepted as Hydractinia Van Beneden, 1844
• Hydractinia (Stylactis) Allman, 1864 accepted as Stylactis Allman, 1864
• Hydractinia (Stylactis) ingolfi Kramp, 1932 accepted as Hydractinia ingolfi (Kramp, 1932)
• Hydractinia aculeata (Wagner, 1833)
• Hydractinia aggregata Fraser, 1911
• Hydractinia alderi (Hodge, 1863) accepted as Podocoryna alderi Hodge, 1863
• Hydractinia allmanii Bonnevie, 1898 accepted as Schuchertinia allmanii (Bonnevie, 1898)
• Hydractinia altispina Millard, 1955
• Hydractinia americana (Mayer, 1910) accepted as Podocoryna americana (Mayer, 1910)
• Hydractinia anechinata (Ritchie, 1907) accepted as Podocoryna anechinata Ritchie, 1907
• Hydractinia angusta Hartlaub, 1904
• Hydractinia antonii Miglietta, 2006 accepted as Schuchertinia antonii (Miglietta, 2006)
• Hydractinia apicata (Kramp, 1959) accepted as Podocoryna apicata Kramp, 1959
• Hydractinia arctica (Jäderholm, 1902)
• Hydractinia areolata Alder, 1862 accepted as Podocoryna areolata (Alder, 1862)
• Hydractinia arge (Clarke, 1882)
• Hydractinia armata Fraser, 1940
• Hydractinia australis (Schuchert, 1996) accepted as Podocoryna australis Schuchert, 1996
• Hydractinia bayeri Hirohito, 1984
• Hydractinia bella (Hand, 1961) accepted as Podocoryna bella Hand, 1961
• Hydractinia betkensis (Watson, 1978)
• Hydractinia borealis (Mayer, 1900) accepted as Podocoryna borealis (Mayer, 1900)
• Hydractinia borealis (Mereschkowsky, 1878) accepted as Oorhiza borealis Mereschkowsky, 1878
• Hydractinia brachyurae (Hirohito, 1988)
• Hydractinia calcarea Carter, 1877 accepted as Hydrocorella calcarea (Carter, 1977)
• Hydractinia calderi Bouillon, Medel & Peña Cantero, 1997 accepted as Hydractinia proboscidea (Hincks, 1868)
• Hydractinia californica Torrey, 1904
• Hydractinia canalifera Millard, 1957
• Hydractinia carcinicola (Hiro, 1939) accepted as Bouillonactinia carcinicola (Hiro, 1939)
• Hydractinia carica Bergh, 1887
• Hydractinia carnea (M. Sars, 1846) accepted as Podocoryna carnea M. Sars, 1846
• Hydractinia carnea var. mediterranea Neppi, 1917 accepted as Hydractinia exigua (Haeckel, 1880) accepted as Podocoryna exigua (Haeckel, 1880)
• Hydractinia carolinae Fraser, 1912
• Hydractinia clavata Jäderholm, 1905 accepted as Perarella clavata (Jäderholm, 1905)
• Hydractinia claviformis (Bouillon, 1965) accepted as Hydractinia proboscidea (Hincks, 1868)
• Hydractinia conchicola (Yamada, 1947) accepted as Schuchertinia conchicola (Yamada, 1947)
• Hydractinia constrictura Huang, Xu & Guo, 2015 (unaccepted > unavailable name)
• Hydractinia cryptogonia Hirohito, 1988
• Hydractinia cytaeiformis Vervoort, 2006
• Hydractinia dendritica Hickson & Gravely, 1907
• Hydractinia denhami (Thornely, 1904) accepted as Podocoryna denhami Thornely, 1904
• Hydractinia diogenes Millard, 1959
• Hydractinia disjuncta Fraser, 1938
• Hydractinia dongshanensis Xu & Huang, 2006 accepted as Podocoryna dongshanensis (Xu & Huang, 2006)
• Hydractinia dubia (Mayer, 1900) accepted as Podocoryna dubia (Mayer, 1900)
• Hydractinia echinata (Fleming, 1828)
• Hydractinia epiconcha Stechow, 1908 accepted as Schuchertinia epiconcha (Stechow, 1908)
• Hydractinia epidocleensis Leloup, 1931
• Hydractinia epispongia Fraser, 1938
• Hydractinia exigua (Haeckel, 1880) accepted as Podocoryna exigua (Haeckel, 1880)
• Hydractinia fallax Broch, 1914 accepted as Perarella fallax (Broch, 1914)
• Hydractinia fucicola (Sars, 1857) accepted as Stylactis fucicola (M. Sars, 1857)
• Hydractinia fuciola (M. Sars, 1857) accepted as Hydractinia fucicola (Sars, 1857) accepted as Stylactis fucicola (M. Sars, 1857)
• Hydractinia galeai Calder & Watling, 2021
• Hydractinia gelinea Watson, 2015
• Hydractinia gorgonoides (Nutting, 1906)
• Hydractinia granulata Hirohito, 1988
• Hydractinia grisea Leuckart, 1847 accepted as Hydractinia echinata (Fleming, 1828)
• Hydractinia guangxiensis Huang, Li & Zhang, 2010 accepted as Podocoryna guangxiensis (Huang, Li & Zhang, 2010)
• Hydractinia hancocki Fraser, 1938
• Hydractinia hayamaensis (Hirohito, 1988) accepted as Podocoryna hayamaensis Hirohito, 1988
• Hydractinia hooperii (Sigerfoos, 1899) accepted as Bouillonactinia hooperii (Sigerfoos, 1899)
• Hydractinia humilis (Hartlaub, 1905) accepted as Podocoryna humilis Hartlaub, 1905 accepted as Podocoryna tenuis (Browne, 1902)
• Hydractinia humilis Bonnevie, 1898 (uncertain > taxon inquirendum)
• Hydractinia inabai (Hirohito, 1988) accepted as Bouillonactinia misakiensis (Iwasa, 1934)
• Hydractinia incerta Van Beneden, 1867 (uncertain > taxon inquirendum)
• Hydractinia inermis (Allman, 1872) accepted as Stylactis inermis Allman, 1872
• Hydractinia ingolfi (Kramp, 1932)
• Hydractinia kaffraria Millard, 1955
• Hydractinia lactea Van Beneden, 1844 accepted as Hydractinia echinata (Fleming, 1828)
• Hydractinia laevispina Fraser, 1922
• Hydractinia leizhouensis Huang, Zhang & Yang, 2020 accepted as Podocoryna leizhouensis (Huang, Zhang & Yang, 2020)
• Hydractinia longispina Fraser, 1938
• Hydractinia mar (Gasca & Calder, 1993)
• Hydractinia marsupialia Millard, 1975
• Hydractinia meteoris (Thiel, 1938) accepted as Paracytaeis meteoris (Thiel, 1938)
• Hydractinia michaelseni Broch, 1914
• Hydractinia milleri Torrey, 1902 accepted as Schuchertinia milleri (Torrey, 1902)
• Hydractinia minima (Trinci, 1903) accepted as Podocorynoides minima (Trinci, 1903)
• Hydractinia minoi (Alcock, 1892)
• Hydractinia minuta (Mayer, 1900) accepted as Lizzia blondina Forbes, 1848
• Hydractinia minuta Bonnevie, 1898 accepted as Hydractinia carica Bergh, 1887
• Hydractinia misakiensis (Iwasa, 1934) accepted as Bouillonactinia misakiensis (Iwasa, 1934)
• Hydractinia moniliformis Huang, Zhong & Zhang, 2010 accepted as Podocoryna moniliformis (Huang, Zhong & Zhang, 2010)
• Hydractinia monocarpa Allman, 1876
• Hydractinia monoon (Hirohito, 1988)
• Hydractinia multigranosi (Namikawa, 1991) accepted as Bouillonactinia multigranosi (Namikawa, 1991)
• Hydractinia multispina Fraser, 1938
• Hydractinia multitentaculata (Millard, 1975)
• Hydractinia munita (Calder, 2010)
• Hydractinia nagaoensis Bouillon, Medel & Peña Cantero, 1997
• Hydractinia nassa (Millard, 1959) accepted as Cytaeis nassa (Millard, 1959)
• Hydractinia novaezelandiae Schuchert, 1996
• Hydractinia ocalana (Brooks, 1964) † accepted as Cystactinia ocalana Brooks, 1964 †
• Hydractinia ocellata (Agassiz & Mayer, 1902) accepted as Podocoryna ocellata (Agassiz & Mayer, 1902)
• Hydractinia ornata Bonnevie, 1899 accepted as Hydractinia allmanii Bonnevie, 1898 accepted as Schuchertinia allmanii (Bonnevie, 1898)
• Hydractinia otagoensis (Schuchert, 1996)
• Hydractinia pacifica Hartlaub, 1905
• Hydractinia parvispina Hartlaub, 1905