Molecular systematics of the deep-sea fish genus Gonostoma (Stomiiformes :Gonostomatidae): Two paraphyletic clades and resurrection of Sigmops

A recent morphological analysis demonstrated that Cyclothone, one of four c urrently recognized gonostomatid genera, was nested within Gonostoma, rende ring the Latter paraphyletic, In an attempt to resolve the interrelationshi ps of Gonostoma and Cyclothone using molecular data, we determined the nucl eotide sequences of a portion of the mitochondrially encoded 12S and 16S ri bosomal RNA genes From 11 gonostomatids, including all seven valid Gonostom a species, and Diplophos taenia as an outgroup, Secondary structure-based a lignment resulted in a character matrix consisting of 566 base pairs of una mbiguously aligned sequences from the two genes, which were subjected to ph ylogenetic analyses using maximum-parsimony and maximum-likelihood methods. The resultant tree topologies from the two methods were congruent, with ma ny nodes being strongly supported by various tree statistics. As in the mor phological analysis, the molecular data indicated the monophyly of Gonostom a + Cyclothone and paraphyly of Gonostoma, although the intrarelationships of Gonostoma differed greatly from those suggested by the morphological dat a. The molecular data supported the existence of two basal, paraphyletic cl ades within Gonostoma, the first comprising two light-colored species (G. a tlanticum. G. denudatum) and representing a sister clade of Cyclothone, and the second, five dark-colored species (G. ebelingi, G. elongatum, G. longi pinnis, G. gracile, G. bathyphilum). Although several alternative classific ations exist that reflect the molecular phylogeny, the resurrection of Sigm ops Gill, 1883 for the clade of Gonostoma comprising five dark-colored spec ies is proposed to maximize the information content in the classification.