Atlantic Haleciidae and Campanulariidae (Hydrozoa, Cnidaria) collected during the CANCAP and Mauritania-II expeditions of the National Museum of Natural History, Leiden, The Netherlands

Twenty-one (sub)species of Leptolida (Hydrozoa, Cnidaria) of the familes Haleciidae and Campanulariidae are described and figured, originating from collections made during the CANCAP and Mauritania- II expeditions of the Rijksmuseum van Natuurlijke Historie (now Nationaal Natuurhistorisch Museum) to the north-eastern Atlantic in the years 1976-1988, visiting waters around the Azores, Canary Islands, Madeira, Cape Verde Islands and off Morocco and Mauritania. This material largely concerns well known species, the majority of which needs no detailed description. Exceptions are i.a. Halecium liouvillei Billard, 1934, Halecium sibogae marocanum Billard, 1934, Clytia arborescens Pictet, 1893, and Laomedea pseudodichotoma Vervoort, 1959. These species are described in more detail as their distributional area is extended. Of all species extensive literature references are given and the geographical distribution is discussed in detail.