The Beryciformes are small- to medium-sized, spiny-rayed fishes, 3-24 in (8-61 cm) long. They have big eyes, some have colorful scales, and some have light organs beneath the eyes. The order is also defined partly by the number of softer, flexible rays in the ventral fin.
Schooling in whitetip soldierfish. (Illustration by Wendy Baker)
gan under each eye. These fishes and the bioluminescent bacteria that generate the light have developed a symbiotic relationship that offers the bacteria a place to live, while giving the fishes illumination, perhaps for attracting zooplankton during night feeding and for intraspecific communication. Light organs are also seen in other beryciform fishes, including those in the family Monocentridae.
The monocentrids' whimsical common names of the pineapple and pineconefishes come from their beautiful, large scales. Usually yellow, each scale has its own dark outline, further accentuating an armorlike appearance. Like the holo-centrids, species of the Monocentridae have spines poking backward from each scale.
Trachichthyids are known mostly from one species, the orange roughy (Hoplostethus atlanticus). This somewhat primitive-looking fish, as well as other members of this family, are distinguished by mucous cavities just beneath the skin of the head. This trait accounts for their less-than-flattering alternate common name of slimeheads.
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