The morphology and phylogenetic significance of Kerygmachela kierkegaardi Budd (Buen Formation, Lower Cambrian, N Greenland)

Specimens of Kerygmnchela kierkegaardi Budd are described, from the Lower C ambrian Sirius Passet fauna of N Greenland. The cephalic region is characte rised by a pair of stout unsegmented appendages each bearing long spinose p rocesses, and an anterior mouth. The trunk shows alternating rows of tuberc les and transverse annulations along the axis, to which are attached 11 pai rs of gill-bearing lateral lobes and lobopodous limbs. The caudal region is small, and bears two long tail spines. There is some evidence for circular musculature arranged around the trunk and a dorsal, longitudinal sinus, an d several details of the muscular pharynx have been preserved. The combination of characters found in Kerygmachela allows it to be allied with the lobopods, represented in the extant fauna by the onychophorans, ta rdigrades, and possibly the pentastomids, and in the Cambrian fossil record by a morphologically diverse set of taxa, some of which are not assignable to the extant groupings. It also shares important characters with the prev iously problematic Burgess Shale forms Opabinia regalis Walcott and Anamalo caris Whiteaves, and the Sirius Passet form Pambdelurion Budd. These taxa t ogether form a paraphyletic group at the base of the clade of biramous arth ropods. The position of the so-called 'Uniramia' remains unclear. It can be demonstrated from the reconstruction of the arthropod stem-group that full arthropod segmentation has a different derivation from that of the annelid s. In line with other recent analyses, this suggests that the 'Articulata' of Cuvier should be dismantled, and the arthropods considered to be a group of protostomes which are phylogenetically distinct from the classic spiral ians. Arthropod affinities may rather lie with the other moulting animals, in the so-called 'Ecdysozoa'.