Taxonomic revision and systematic notes on someHaleciumspecies (Cnidaria, Hydrozoa)

Although the genus Halecium is easy to recognize, identifications at the species level are often difficult, this even for quite common and supposedly well-known species of the north-eastern Atlantic. This paper revises and re-describes some Halecium species which resemble each other closely and which are not easy to distinguish. Additional information on a few rare species is also provided. The study is based on material collected from the North Atlantic, Mediterranean, South Africa, and New Zealand. Halecium scutum Clark, 1877 is recognized as a valid species and distinct from both H. beanii and H. halecinum; colony form and microscopic characters allow a distinction. The pinnate colony form of H. halecinum is a characteristic trait, but not all colonies show this growth form. Halecium beanii can occur in monosiphonic and polysiphonic colonies. Monosiphonic colonies of H. beanii have probably been misidentified by some authors as H. lankesterii. The differences of H. lankesteri to H. beanii and H. petrosum are discussed. The South African population of the reportedly cosmopolitan H. beanii has distinct gonothecae and could belong to a separate species. The Mediterranean Halecium mediterraneum is hardly distinguishable from the New Zealandic H. delicatulum, but it is kept separate mainly for biogeographic reasons. The rare Mediterranean Halecium banyulense is redescribed based on a second find from Naples. The male gonothecae of Halecium corrugatissimum are described for the first time.