Morphological and Molecular Characteristics of Longicollum alemniscus (Acanthocephala: Echinorhynchida), with a Taxonomic Revision of the Genus Longicollum

The acanthocephalan genus <i>Longicollum</i> Yamaguti, 1935 currently comprises 12 fish-parasitic species. Except for <i>L. pagrosomi</i> Yamaguti, 1935, the remaining 11 congeners have not been the subject of molecular phylogenetic studies. <i>Longicollum alemniscus</i> (Harada, 1935) has been found in brackish and marine fish in Taiwan and Japan, but its morphology remains inadequately understood. In this paper, we provide a morphological redescription and infer the phylogenetic position of <i>L. alemniscus</i> within the Pomphorhynchidae. Furthermore, we summarize the morphological characteristics of <i>Longicollum</i> to distinguish it from the morphologically similar genus <i>Paralongicollum</i> Amin, Bauer, and Sidorov, 1991.