The ragfish became known to science in 1880, when Lockington obtained two juvenile specimens from a fish market in San Francisco. The two specimens were unfortunately lost in a fire caused by an earthquake that devastated California in 1906.
Lockington described the ragfish as being nearly scaleless (only spinous scales on the lateral line) with bony prickles on the fin rays of each fin. Purple spots and blotches are distributed over a yellowish-brown ground colour, a round caudal fin, and small pelvic fins.
Seven years later Tartelton H. Bean received a large fish (approximately 182cm) from Mr. Charles Willoughby that was beached in Damon, in the State of Washington. Bean recognised the close resemblance to the ragfish. However because of some differences to the ragfish, Bean described it as Acrotus willoughbyi, in honour of its finder, in 1888.
73 years later Clemens and Wilby realised that Icosteus aenigmaticus and Acrotus willoughbyi represent the juveniles and adults of the same species.
Still the relationship of the ragfish to other fish remains enigmatic. Many systematics researchers have placed the ragfish close to the butterfishes and their relatives (Stromateoidei), which it resembles superficially.
However morphologically the ragfish is a mixture between the whalefishes and their relatives