[1] Some of the most famous species of radiodonts are the Cambrian taxa Anomalocaris canadensis, Hurdia victoria, Peytoia nathorsti, Titanokorys gainesi, Cambroraster falcatus and Amplectobelua symbrachiata.

[3][4] The original diagnosis of order Radiodonta in 1996 is as follows:[2] Radiodontids are bilaterally symmetrical, elongate arthropods with a nonmineralized cuticle typically most robust in the jaws and claws.

The trunk is metameric, typically with about 13 segments laterally developing imbricating lobes for swimming and gills for respiration, and may end in a prominent three-part tail.

[21][19] The mouth is on the ventral side of the head, behind the attachment point of frontal appendages and is surrounded by a ring of tooth plates, forming the mouthpart known as oral cone ('jaws' in previous studies[2]).

[6] The head bore two stalked compound eyes, which may have had mobility,[25] and are located between the gaps formed by the posterior regions of the H-element and P-elements.

In some species, jaw-like feeding appendages called gnathobase-like structures (GLSs) arose from each of the bases of their reduced neck flaps.

[22] In both interpretations, posterior to the brain was a pair of apparently unfused ventral nerve cords which ran through the animal's neck region.

The muscular, overlapping ventral flaps may have propelled the animal through the water, possibly by moving in a wave-like formation resembling modern rays and cuttlefish.

[36] On the other hand, some hurdiids have features significantly specialized for a nektobenthic lifestyle, such as Cambroraster with its dome-like H-element similar to the carapace of a horseshoe crab.

[27][11] Abundance of the remains of scleritzed structures such as disarticulated frontal appendages and head sclerite complexes, suggest that mass moulting events may have occurred among radiodonts,[11][6] a behavior which also has been reported in some other Cambrian arthropods such as trilobites.

[26][21][3][1] With the smaller head carapace complex and large surface of arthrodial membranes, frontal appendages of these taxa had greater flexibility.

[6][1] Endites of frontal appendages from suspension/filter feeders like Tamisiocaris and Aegirocassis have flexible, densely-packed auxiliary spines, which could filter out organic components such as mesozooplankton and phytoplankton down to 0.5mm.

[5][11] Frontal appendages of Caryosyntrips, which are unusual for radiodonts in having the direction of endite-bearing surfaces opposing one another and may have been able to manipulate and crush prey in a scissor-like slicing or grasping motion.

[23][38][6] Priapulida and relatives Onychophora Tardigrada Lobopodian grade(paraphyletic) Siberiid lobopodians Pambdelurion Kerygmachela Opabiniidae Radiodonta Euarthropoda Most phylogenetic analyses suggest that radiodonts, alongside opabiniids (Opabinia and Utaurora[44]), are stem-group arthropods just basal to deuteropoda,[42] a clade including upper stem (e.g. fuxianhuiids and bivalved arthropods) and crown Euarthropoda (e.g. Artiopoda, Chelicerata and Mandibulata).

[42][53][54] The constricted neck region with feeding appendicular structures of some radiodont may also shed light on the origin of the sophisticated arthropod head, which was formed by the fusion of multiple anterior body segments.

[3][17] Basal deuteropods that possess a mixture of radiodont/opabiniid characters like Kylinxia and Erratus, may represent intermediate forms between radiodonts, opabiniids and other euarthropods.

Peytoia Stanleycaris Schinderhannes Aegirocassis Hurdia Pahvantia Cambroraster Titanokorys Cordaticaris Euarthropoda Traditionally, all radiodont species have been placed within one family, Anomalocarididae,[2] hence the previous common name 'anomalocaridid'[26][9] and it was still occasionally used to refer the whole order even after reclassification.

[5] The original description of the order Radiodonta included Anomalocaris, Laggania (later known as Peytoia), Hurdia, Proboscicaris, Amplectobelua, Cucumericrus, and Parapeytoia.

[65] With the exclusion of questionable Caryosyntrips and Cucumericrus, the monophyly of Radiodonta is widely supported,[5][10][11][7][13][6][39][40] with a few results suggest possible paraphyly (either the Anomalocarididae+Amplectobeluidae clade or Hurdiidae sister to Euarthropoda).

[4][6][40] Monophyly of the speciose family Hurdiidae was recovered by most analysis and well-supported by several synapomorphies (e.g. distal articulated region of frontal appendage with proximal 5 podomeres bearing subequal endites[19][6]).

[2][9] Prior to their recognition as a group, radiodont specimens had been assigned to five different phyla: Porifera, Cnidaria, Echinodermata, Annelida, and Arthropoda.

[86] The Geological Survey of Canada initiated a revision of Burgess Shale fossils in 1966, overseen by Cambridge University paleontologist Harry B.

In 1978, Simon Conway Morris recognized that the mouthparts of Laggania were Peytoia-like, but he interpreted this as evidence that it was a composite fossil made up of a Peytoia jellyfish and a sponge.

[9] Even after these recognitions, partial misidentifications (e.g. oral cone and frontal appendages of Peytoia had been assigned to Anomalocaris[2] and Hurdia,[9] respectively) had been revealed by subsequent studies as well.

[23][89] The taxon Radiodonta itself was coined in 1996 by Desmond Collins, after it was established that Anomalocaris and its kin represented a distinctive lineage with arthropod affinities rather than a hitherto unknown phylum.

[90] Until the 2010s, radiodonts were typically considered to be uniformly large apex predators, but discoveries of new species over the course of that decade led to a considerable increase in the known ecological and morphological diversity of the group.