Acaulis primarius Stimpson, 1853 (redescription)
Acauloides ammisatum Bouillon, 1965 (redescription)
Amphinema dinema (Péron & Lesueur, 1810) (redescription)
Amphinema rugosum (Mayer, 1900) (redescription)
Annatiara affinis (Hartlaub, 1914) (redescription)
Bimeria vestita Wright, 1859 (redescription)
Boreohydra simplex Westblad, 1937 accepted as Plotocnide borealis Wagner, 1885 (redescription)
Bougainvillia britannica (Forbes, 1841) (redescription)
Bougainvillia macloviana Lesson, 1830 (redescription)
Bougainvillia muscoides (Sars, 1846) (redescription)
Bougainvillia muscus (Allman, 1863) (redescription)
Bougainvillia principis (Steenstrup, 1850) (redescription)
Bougainvillia pyramidata (Forbes & Goodsir, 1853) (redescription)
Bougainvillia superciliaris (L. Agassiz, 1849) (redescription)
Candelabrum cocksii (Cocks, 1854) (redescription)
Candelabrum phrygium (Fabricius, 1780) (additional source)
Catablema vesicarium (A. Agassiz, 1862) (redescription)
Cladocoryne floccosa Rotch, 1871 (redescription)
Cladonema radiatum Dujardin, 1843 (redescription)
Clava multicornis (Forsskål, 1775) (redescription)
Codonium proliferum (Forbes, 1848) (redescription)
Cordylophora caspia (Pallas, 1771) (redescription)
Corydendrium dispar Kramp, 1935 (redescription)
Corymorpha nana Alder, 1857 (redescription)
Corymorpha nutans M. Sars, 1835 (redescription)
Coryne eximia Allman, 1859 (additional source)
Coryne eximia Allman, 1859 (redescription)
Coryne fucicola (de Filipi, 1866) (redescription)
Coryne muscoides (Linnaeus, 1761) (redescription)
Coryne pintneri Schneider, 1897 (redescription)
Coryne pusilla Gaertner, 1774 (redescription)
Dicoryne conferta (Alder, 1856) (redescription)
Dicoryne conybearei (Allman, 1864) (redescription)
Ectopleura L. Agassiz, 1862 (redescription)
Ectopleura crocea (Agassiz, 1862) (redescription)
Ectopleura dumortierii (Van Beneden, 1844) (redescription)
Ectopleura larynx (Ellis & Solander, 1786) (redescription)
Ectopleura wrighti Petersen, 1979 (redescription)
Eleutheria claparedii Hartlaub, 1889 (redescription)
Eleutheria dichotoma Quatrefages, 1842 (redescription)
Eucodonium brownei Hartlaub, 1907 (redescription)
Eudendrium album Nutting, 1898 (redescription)
Eudendrium annulatum Norman, 1864 (redescription)
Eudendrium arbuscula Wright, 1859 (redescription)
Eudendrium capillare Alder, 1856 (redescription)
Eudendrium capillaroides Schuchert, 2008 (redescription)
Eudendrium glomeratum Picard, 1952 (redescription)
Eudendrium racemosum (Cavolini, 1785) (redescription)
Eudendrium rameum (Pallas, 1766) (redescription)
Eudendrium ramosum (Linnaeus, 1758) (additional source)
Eudendrium ramosum (Linnaeus, 1758) (redescription)
Eudendrium unispirum Schuchert, 2008 (redescription)
Eudendrium vaginatum Allman, 1863 (redescription)
Eudendrium vervoorti Marques & Migotto, 1998 (additional source)
Euphysa aurata Forbes, 1848 (redescription)
Euphysa tentaculata Linko, 1905 (redescription)
Garveia franciscana (Torrey, 1902) accepted as Calyptospadix cerulea Clarke, 1882 (redescription)
Garveia nutans Wright, 1859 (redescription)
Halitholus cirratus Hartlaub, 1914 (redescription)
Hybocodon prolifer Agassiz, 1860 (redescription)
Hydra circumcincta Schulze, 1914 (redescription)
Hydra oligactis Pallas, 1766 (redescription)
Hydra oxycnida Schulze, 1914 (redescription)
Hydra viridissima Pallas, 1766 (redescription)
Hydra vulgaris Pallas, 1766 (redescription)
Hydractinia areolata Alder, 1862 accepted as Podocoryna areolata (Alder, 1862) (redescription)
Hydractinia echinata (Fleming, 1828) (redescription)
Hydractinia proboscidea (Hincks, 1868) (redescription)
Hydractinia sarsii (Steenstrup, 1850) (redescription)
Hydrichthys sarcotretis (Jungersen, 1913) (redescription)
Koellikerina fasciculata (Péron & Lesueur, 1810) (redescription)
Leuckartiara nobilis Hartlaub, 1914 (redescription)
Leuckartiara octona (Fleming, 1823) (redescription)
Lizzia blondina Forbes, 1848 (redescription)
Margelopsis haeckelii Hartlaub, 1897 (redescription)
Merona cornucopiae (Norman, 1864) (redescription)
Moerisia inkermanica Paltschikowa-Ostroumowa, 1925 (redescription)
Nemopsis bachei L. Agassiz, 1849 (redescription)
Neoturris breviconis (Murbach & Shearer, 1902) (redescription)
Neoturris pileata (Forsskål, 1775) (redescription)
Pachycordyle michaeli (Berrill, 1948) (additional source)
Pachycordyle navis (Millard, 1959) accepted as Pachycordyle michaeli (Berrill, 1948) (redescription)
Pandea conica (Quoy & Gaimard, 1827) (redescription)
Paratiara digitalis Kramp & Damas, 1925 (redescription)
Pliobothrus symmetricus Pourtalès, 1868 (redescription)
Plotocnide borealis Wagner, 1885 (redescription)
Podocoryna areolata (Alder, 1862) (redescription)
Podocoryna borealis (Mayer, 1900) (redescription)
Podocoryna carnea M. Sars, 1846 (redescription)
Podocoryna exigua (Haeckel, 1880) (redescription)
Podocorynoides minima (Trinci, 1903) (redescription)
Proboscidactyla stellata (Forbes, 1846) (redescription)
Protohydra leuckarti Greeff, 1870 (redescription)
Psammohydra nanna Schulz, 1950 (redescription)
Rathkea octopunctata (M. Sars, 1835) (redescription)
Rhizogeton nudus Broch, 1910 (redescription)
Rhizorhagium album Rees, 1938 accepted as Rhizorhagium arenosum (Alder, 1862) (source of synonymy)
Rhizorhagium arenosum (Alder, 1862) (redescription)
Rhizorhagium roseum M. Sars, 1874 (redescription)
Sarsia lovenii (M. Sars, 1846) (redescription)

East Greenland Shelf for Stylaster gemmascens (Esper, 1790) 
Faroe Plateau for Stylaster gemmascens (Esper, 1790) 
North and East Iceland for Stylaster gemmascens (Esper, 1790) 
Southern Norway for Stylaster gemmascens (Esper, 1790) 

 Diagnosis

 for Codonium Haeckel, 1879

Comprises Codonium proliferum (Forbes, 1884) and similar Corynidae with medusa that bud secondary medusae from ... [details]

 Diagnosis

 for Rhizogeton Agassiz, 1862

Stolonal hydroid colonies, polyps monomorphic, hydranths either sessile or with a perisarc-covered pedicel. ... [details]

 Distribution

 for Stylaster gemmascens (Esper, 1790)

North Atlantic from Denmark Strait, east of Greenland, northwest of Iceland through Faroes-Hebrides area to Norway ... [details]

 Taxonomy

 for Protohydridae Allman, 1888

The taxonomic position is unclear due to the very simple morphology. [details]