Phylogenetic systematics of the viviparous halfbeak genera Dermogenys and Nomorhamphus (Teleostei : Hemiramphidae : Zenarchopterinae)

Among the 13 genera and over 100 species of halfbeaks, three genera - Dermo genys, Nomorhamphus and Hemirhamphodon - are internally fertilized and vivi parous. These genera belong to a more inclusive clade, the Zenarchopterinae , that also includes Zenarchopterus, inferred to be internally fertilized a nd to lay fertilized eggs, and the monotypic Tondanichthys, also inferred t o be internally fertilized. Whereas the Hemiramphidae are distributed world wide, internally fertilized halfbeaks are restricted to Southeast Asia. Rec ent data from histological surveys of the gonads of both males and females as well as embryonic modifications associated with viviparity have been com bined here with osteological characters in a phylogenetic analysis. Results indicate overwhelming support for a sister-group relationship between Hemi rhamphodon and (Dermogenys+Nomorhamphus). Monophyly of the Dermogenys+Nomor hamphus clade is also well supported. These results confirm earlier suggest ions that Dermogenys, as previously defined, is paraphyletic. Within the De rmogenys+Nomorhamphus clade, two monophyletic clades are supported: one com prises ten species including four new species (Dermogenys bruneiensis, Derm ogenys robertsi, Dermogenys palawanensis and Dermogenys collettei) and the other comprises 13 species including three undescribed species (Nomorhamphu s rossi, Nomorhamphus pinnimaculata and Nomorhamphus manifesta). Diagnoses for the species of Dermogenys and Nomorhamphus, as well as a natural classi fication for the included species, are presented. (C) 2001 The Linnean Soci ety of London.