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Great appendages are claw-like appendages which attach to the heads of the "great appendage arthropods", a name usually refers to Megacheira, a class of extinct arthropod characterized by a pair of "short-great appendages" bearing in front of the animal's head.
In general, megacheiran's great appendage have 6 segments, with the two proximal segments forming a peduncle and the four finger-like distal segments forming a claw, both connected by an elbow joint. Great appendages have been interpreted as raptorial limbs involved in predation, with those of some genera such as Yohoia being structurally comparable to the raptorial maxillipeds of mantis shrimp. The great appendages of leanchoilid megacheirans such as Leanchoilia and Yawunik have elongated flagella, suggesting a sensory role alongside predatory function.
Radiodont's frontal appendages have controversial relationships to those of the megacheirans. They have been suggested to be homologous with the antennule of the euarthropods , or more specifically the chelicerae of chelicerates, although the latter possibility has been discounted by some authors. As of late 2010s, most studies reject the homology of this two type of frontalmost appendages, with neural structures clarifying the segmental affinities of radiodont frontal appendages as protocerebral , and megacheiran's short-great appendages as deutocerebral. Similar appendages have also been found in other Cambrian arthropods such as Isoxys and Occacaris, but their segmental affinities remain conjectural. On the other hand, some 2020 studies suggested that the frontalmost appendages of radiodonts and euarthropods may be homologous, and that the presence of a raptorial, deutocerebral frontalmost appendage is the ancestral condition for euarthropod itself. Under this scenario, the euarthropod Kylinxia zhangi with frontalmost appendages that possess strong resemblance to those of a radiodont may represent an intermediate form between stem and true arthropods.