The phylogenetic status of the speciose euteleostean assemblage, the Acanthomorpha, is investigated. For the purposes of cladistic analysis attention is centred upon an examination of euteleostean buccal ligament systems, the occipital and ethmoid regions of the neurocranium, and the posttemporal/neurocranial association.
In this study four derived morphological features are identified which support the monophyly of the Acanthomorpha, and the previously ‘problematical’ genus Polymixia is determined to be the sistergroup of all the remaining acanthomorphs. The phylogenetic integrity of the sistergroup of the entire Acanthomorpha, the Myctophiformes (sensu Rosen, 1973), is attested by the presence of four derived features, and the monophyly of its major subdivisions (the Myctophidae and Neoscopelidae) is resolved.
Additional problems of euteleostean systematics and systematic methodology are discussed.