This study reviews all European hydroids belonging to the filiferan family Eudendriidae. Two new species occurring in the northeastern Atlantic are described: Eudendrium capillaroides new spec. and Eudendrium unispirum new spec. Eudendrium vaginatum Allman,1863, is redescribed. It is characterized by a special type of nematocysts and traits of the perisarc. It is distinct from Eudendrium annulatum Norman, 1864, which is a separate, valid species. Eudendrium fragile Motz-Kossowska, 1905 and Eudendrium islandicum Schuchert, 2000 are both recognized as synonyms of E. album Nutting, 1898. Eudendrium stratum Bonnevie, 1898 and E. planum Bonnevie, 1898 are both recognized as
synonyms of E. rameum (Pallas, 1766). Eudendrium insigne Hincks, 1861
is indistinguishable from E. ramosum and newly collected material from the
type locality confirmed this. Eudendrium insigne must thus be regarded as
a synonym of E. ramosum (Linnaeus, 1758). A re-examination of the type
material of Eudendrium elsaeoswaldae Stechow, 1921 revealed that it is
conspecific with E. ramosum (Linnaeus, 1758), becoming thus a new
synonym of the latter. Perigonimus multicornis Allman, 1876 is indistinguishable from Myrionema hargitti (Congdon, 1906) and must be regarded as a senior synonym of the latter. Because it seems likely that the original type locality
designation “Kattegat” was incorrect, it should not replace M. hargitti or M.
amboinense.
