Considering how paleontologists' reconstructions of Opabinia differ, it is not surprising that the animal's classification is highly debated during 20 century.[1] Charles Doolittle Walcott, the original describer, considered it to be an anostracan crustacean in 1912.[2] The idea was followed by G. Evelyn Hutchinson in 1930, providing the first reconstruction of Opabinia as an anostracan swimming upside down.[23] Alberto Simonetta provided a new reconstruction of Opabinia in 1970 very different to those of Hutchinson's, with lots of arthropod feature (e.g. dorsal exoskeleton and jointed limbs) which are reminiscent of Yohoia and Leanchoilia.[24] Leif Størmer, following earlier work by Percy Raymond, thought that Opabinia belonged to the so-called "trilobitoids" (trilobites and similar taxa).