| Species name | Common name | Distribution | Max. Length (cm) |
|---|---|---|---|
| Hydractinia aculeata (Wagner, 1833) |
Mediterranean | ||
| Hydractinia aggregata Fraser, 1911 |
Eastern Pacific | ||
| Hydractinia altispina Millard, 1955 |
High-spined commensal hydroid | Southeast Atlantic | |
| Hydractinia americana (Edwards, 1972) |
Atlantic and Pacific Oceans | ||
| Hydractinia angusta Hartlaub, 1904 |
Antarctic Pacific | ||
| Hydractinia antonii Miglietta, 2006 |
Northwest Pacific | ||
| Hydractinia arge (Clarke, 1882) |
Western Atlantic | ||
| Hydractinia armata Fraser, 1940 |
Eastern Pacific | ||
| Hydractinia californica Torrey, 1904 |
Eastern Pacific | ||
| Hydractinia carica Bergh, 1887 |
Northern Atlantic, Northwest Pacific and Arctic | ||
| Hydractinia carolinae Fraser, 1912 |
Western Atlantic | ||
| Hydractinia dendritica Hickson & Gravely, 1907 |
Antarctic | ||
| Hydractinia dubia (Mayer, 1900) |
Western Atlantic | ||
| Hydractinia echinata (Fleming, 1828) |
Snailfur | Atlantic Ocean and the Mediterranean | |
| Hydractinia fucicola (Sars, 1846) |
Mediterranean | ||
| Hydractinia laevispina Fraser, 1911 |
Northwest Atlantic, Eastern Pacific and Arctic Oceans | ||
| Hydractinia leizhouensis Huang, Zhang et Yang, 2020 |
Northwest Pacific | ||
| Hydractinia milleri Torrey, 1902 |
Miller hydractinia | Eastern Pacific | 2.5 |
| Hydractinia minima (Trinci, 1903) |
Western Atlantic and the Mediterranean | ||
| Hydractinia minuta (Mayer, 1900) |
Western Atlantic, Caribbean, Mediterranean, Sub-Antarctic and temperate waters of northern hemisphere | ||
| Hydractinia monocarpa Allman, 1847 |
Atlantic Ocean, Northwest Pacific and the Arctic | ||
| Hydractinia pacifica Hartlaub, 1905 |
White bottlebrush hydroid | Southeast Pacific | |
| Hydractinia parvispina Hartlaub, 1905 |
Antarctic Atlantic | ||
| Hydractinia polycarpa Fraser, 1938 |
Eastern Pacific | ||
| Hydractinia polyclina Agassiz, 1862 |
Western Atlantic | ||
| Hydractinia selena (Mills, 1976) |
Western Atlantic | ||
| Hydractinia symbiolongicarpus Buss & Yund, 1989 |
Western Atlantic | ||
| Hydractinia symbiopollicaris Buss & Yund, 1989 |
Western Atlantic | ||
| Hydractinia valens Fraser, 1941 |
Western Atlantic |