What causes transformation of the parasitic copepod? A new example of host switching in the family Anthessiidae (Cyclopoida) from Singaporean waters, with the proposal of a new genus

Merlionia zeeae , a new species belonging to a new genus, is described as a member of the cyclopoid family Anthessiidae (Copepoda), based on both sexes collected off the coast of Singapore. The new species was found in the gill cavities of the longnosed stargazer, Ichthyscopus lebeck (Actinopteri: Perciformes: Uranoscopidae), although almost all members of the family are associated with molluscan hosts. However, this copepod is not similar to other genera of the family Anthessiidae due to possessing the following characters: the curved hook-like antenna, which is similar to that of the family Chondracanthidae in both sexes; the distal portion of the maxilla covered with numerous spinules; and the lack of the maxilliped in the female. Both maximum likelihood and Bayesian inferences using partial SSU (18S) ribosomal RNA genes strongly supported a monophyletic clade formed by the new genus, and three anthessiid genera in this study. However, it was not supported that Anthessiidae and Chondracanthidae are closely related. Therefore, the new genus is considered to be a highly transformed member of the former, and the chondracanthid-form antenna might therefore be a product of convergent evolution attributable to the host-switching event from molluscs to fishes.