Evolution and systematics

The order Stephanoberyciformes comprises deepwater, bathypelagic fishes that are for the most part poorly known anatomically. The order has a checkered systematic history; some of the families currently assigned to this order were treated as part of the formerly larger order Beryciformes (sometimes called Trachichthyiformes), others were previously included in the Lampridiformes. Stephanoberyciforms, as presently constituted, were given the status of an order by G. D. Johnson and C. Patterson in a phylogenetic survey of acanthomorph teleosts in 1993 (which is followed here); parts of the group were previously recognized as separate orders by earlier authors, including the whalefishes (Cetomim-iformes) and pricklefishes and allies (Xenoberyces in part, or Stephanoberyciformes sensu stricto).

The 9 families that form the Stephanoberyciformes are divided into 28 genera and about 92 species. The families are:

• Stephanoberycidae (pricklefishes; 3 monotypic genera)

• Melamphaidae (bigscales or ridgeheads; 5 genera, about 38 species)

• Gibberichthyidae (gibberfishes, Gibberichthys; 2 species)

• Hispidoberycidae (Hispidoberyx ambagiosus)

• Cetomimidae (flabby whalefishes; 9 genera, about 35 species)

• Barbourisiidae (Barbourisia rufa)

• Rondeletiidae (redmouth whalefishes, Rondeletia; 2 species)

• Mirapinnidae (3 genera, 5 species)

• Megalomycteridae (largenoses; 4 genera, 5 species)

The first four families form the superfamily Stephanobery-coidea; the remaining families are united in the Cetomi-moidea. Stephanoberyciforms share a specialization of the posterior dermal skull roof, in which the enlarged ex-trascapular bones cover the parietal bones. They are closely related to the bony fish groups Zeiformes, Beryciformes (sensu stricto), and Percomorpha, sharing with them the presence of pelvic fin spines (lost in certain stephanoberyciforms), as well as specialized features of their pelvic fin anatomy.

The fossil history of the Stephanoberyciformes is almost negligible in contrast to the more extensive fossil history of the Beryciformes. No fossil stephanoberyciform taxon has been erected to date, even though fossil otoliths (paired ear stones of the membranous inner ear labyrinth present in many fishes that can aid in detecting motion) and scant skeletal remains have been mentioned. Otoliths are difficult to identify because they lack features that are diagnostic of taxa of fishes; nonetheless, two unnamed species referred to the living genus Melamphaes have been recorded from the Tertiary period (some 50 million years ago) of France.

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