Lampriformes is an order of ray-finned fish. They are collectively called "lamprids" (which is more properly used for the Lampridae) or lampriforms, and unite such open-ocean and partially deep-sea Teleostei as the crestfishes, oarfish, opahs and ribbonfishes. A synonym for this order is Allotriognathi, while an often-seen but apparently incorrect spelling variant is Lampridiformes. They contain 7 extant families which are generally small but highly distinct, and a mere 12 lampriforms genera with some 20 species altogether are recognized.
The scientific name literally means "Shaped (like the) bright (one)". But as "Lampr-", meaning bright, comes from Lampris the generic name for the Opah, then "opah-shaped" would be a more meaningful translation. In fact, most living lampriforms are actually ribbon-like and not very similar to the disc-shaped opahs in habitus. They are, however, quite distinctly united by their anatomy, and the family's phylogeny as well as the most ancient fossils of this order suggest that the original lampriform was indeed rather "opah-shaped". The scientific name is a combination of Lampris (the type genus) + the standard fish order suffix "-formes". It ultimately derives from Ancient Greek lamprós (λαμπρός, "bright") + Latin forma ("external form"), the former in reference to brilliant coloration of opahs.
Description and ecology
The lampriforms have 84-96 total vertebrae; an orbitosphenoid bone is present in some members of this order. Their premaxilla completely excludes the maxilla from the gape, but the jaws are highly protrusible nonetheless. The upper jaw's protrusion is achieved in a unique way: the maxilla, instead of being ligamentously attached to the ethmoid and palatine, slides in and out with the highly protractile premaxilla. The pelvic fins have up to 17 rays and are placed rather far toward the front of the animal, but they can be missing entirely. The dorsal fin is long, and tend to extend along most of the length of the body. Fin spines are absent in all. Some have a physoclistous gas bladder, while others have none. They either have tiny scales or naked skin.
Systematics and evolution
The order Lampriformes is anatomically similar to some Acanthopterygii at a first glance. But more detailed studies reveal that they are not as advanced, and many authors assign them to a basal position inside the advanced spiny-rayed Teleostei clade called Acanthomorpha, as monotypic superorder "Lampridiomorpha". Unlike their presumed relatives they lack fin spines, however, and other authors have considered them to form a lineage just outside the Acanthomorpha, and the sister taxon of the Myctophiformes. Molecular data also supports the view that the Lampriformes are close to the advanced Teleostei. But the data does not agree on their exact relationships, and the Myctophiformes are also inferred to be close to the Protacanthopterygii, one of the core groups of moderately advanced teleosts. As modern taxonomy tries to avoid a profusion of small taxa, and the delimitation of the Euteleostei (Protacanthopterygii sensu stricto and their allies) versus Acanthopterygii remains uncertain, the systematics and taxonomy of the Lampriformes among the teleosts are in need of further study.
The lampriforms diverged from other teleosts in the Cretaceous, perhaps 80 Ma (million years ago) or slightly more, considering that the oldest known lampriforms, Nardovelifer, dates from the late Campanian epoch and is already clearly assignable to the present order. The basal lampriforms were bathysomes, while the taeniosome body shape is apomorphic and seems to have evolved only once. The order underwent its main radiation in the Paleocene period; the opah-like Turkmenidae were a family of lampriforms thriving at that time, but going extinct around the start of the Neogene, about 23 Ma. Other fossil Lampridiformes are Bajaichthys, Palaeocentrotus and Veronavelifer.
Basal and incertae sedis
* Genus Bajaichthys (fossil)
* Family Stylephoridae — Tube-eye or Thread-tail (monotypic)
1. ^ Nelson (2006): pp.226,228
* Diogo, Rui (2008): On the cephalic and pectoral girdle muscles of the deep sea fish Alepocephalus rostratus, with comments on the functional morphology and phylogenetic relationships of the Alepocephaloidei (Teleostei). Anim. Biol. 58(1): 23-29. doi:10.1163/157075608X303636
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