Abstract
We report on Scorpidotrema longistipes and two new species belonging to a new genus: Holsworthotrema enboubal ichthys gen. et sp. nov. and Holsworthotrema chaoderma sp. nov. These taxa are the first representatives of the subfamily Stenakrinae included in molecular phylogenetic analyses of the Opecoelidae. They resolve among the deep-sea + freshwater Plagioporinae (s.l.) clade, but exploit shallow-water marine fishes. Based on phylogeny, ecology and morphology, we reorganize this clade into four subfamilies: the Plagioporinae (s.s.) for freshwater taxa, the Stenakrinae as currently defined with the addition of Holsworthotrema, the Bathycreadiinae subf. nov. for Bathycreadium and the Podocotylinae, a resurrected concept, for Podocotyle, Bathypodocotyle gen. nov., Buticulotrema, Halosaurotrema gen. nov., Macrourimegatrema, Neolebouria and Tellervotrema. Bathypodocotyle is proposed for species from deep-sea fishes previously assigned to Allopodocotyle, and Halosaurotrema for Gaevskajatrema halosauropsi. Two deep-sea opecoelids represented by sequence data, Neolebouria lanceolata and Podocotyloides brevis, remain inadequately accommodated. These taxa are sister to the Stenakrinae and may require another new subfamily, but it is not yet clear which morphological and/or ecological characters would distinguish such a concept. Evidently, neither belongs to its nominal genus; we propose to accommodate these taxa in Mesobathylebouria gen. nov. and Abyssopedunculus gen. nov., respectively.
