[3] Primarily known from mesopelagic waters, an unidentified species of Ateleopus was observed in the Java and Mariana Trenches in the southwest Pacific at hadal depths up to 6,737 metres (22,103 ft), extending the depth range of the family by 5,500 metres (18,000 ft)[4] Jellynose skeletons are largely cartilage (hence 'jellynose'), although they are true teleosts and not closely related to Chondrichthyes.

Whether it is indeed justified to accept such a small group is doubtful; it may well be that the closest living relatives of the "Stenopterygii" are found among the superorder Protacanthopterygii, and that the former would need to be merged in the latter.

In some classifications, the "Stenopterygii" are kept separate but included with the Protacanthopterygii and the monotypic superorder Cyclosquamata in an unranked clade called Euteleostei.

That would probably require splitting two additional monotypic superorders out of the Protacanthopterygii, and is probably not ideal due to the profusion of very small taxa it would create.

The relationships of these to the taxa mentioned before is still not well resolved at all, and regardless whether one calls them Protacanthopterygii sensu lato or Euteleostei, the phylogeny of this group of moderately advanced Teleostei is in need of further study.