Scales absent; swim bladder absent; dorsal and anal fins confluent; dorsal fin origin posterior, well behind pectoral fin; eyes poorly developed; opercular spine weak or absent; no sensory pores on head; pyloric caeca absent; pelvics jugular, one ray in each (absent in a few species); ovaries bilobed; precaudal vertebrae 26-48 (total of 68-86 vertebrae). A number of neotenic characters are present. Most species occur in depths exceeding 700 m.
Six genera, Aphyonus, Barathronus, Meteoria, Nybelinella, Parasciadonus, and Sciadonus, with 22 species (Nielsen et al., 1999).
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