Abstract
Identification of hydrozoans of the family Cytaeididae L. Agassiz, 1862 is confused due to their morphological similarity, to the shortage of morphological characteristics, and to a lack of molecular data. In this study, sequences of nuclear and mitochondrial DNA markers were analyzed from hydroids of Cytaeis Eschscholtz, 1829 collected in the southern Red Sea on shells of Nassarius Dum,ril, 1805 (Gastropoda: Nassariidae), along with sequences of Cytaeis and Perarella Stechow, 1922 from GenBank. Analyses revealed the paraphyly of the family Cytaeididae, and indicate that the genus Cytaeis may actually belong to the family Bougainvilliidae Lutken, 1850 (Hydrozoa: Anthoathecata). Perarella species grouped within different families and far from Cytaeis species within phylogenetic trees. Additional studies are necessary to confirm the phylogenetic position and formally revise the taxonomy of Perarella. These results demonstrate the need to utilize molecular sequences in re-assessing the taxonomy and phylogeny of filiferan hydrozoans.