Peytoia
Peytoia is a genus of hurdiid radiodont, an early diverging order of stem-group arthropods, that lived in the Cambrian period, containing two species, Peytoia nathorsti from the Miaolingian of Canada and Peytoia infercambriensis from Poland, dating to Cambrian Stage 3.[1] Its two frontal appendages had long bristle-like spines, it had no fan tail, and its short stalked eyes were behind its large head.
108 specimens of Peytoia are known from the Greater Phyllopod bed, where they comprise 0.21% of the community.[2]
Peytoia nathorsti and its junior synonym Laggania cambria played a major role in the discovery of the radiodont body plan. Initially interpreted as a jellyfish and a sea cucumber respectively, they were eventually shown to be the mouthparts and body of a single animal, which bore Anomalocaris-like appendages.
Peytoia contains two named species: Peytoia nathorsti, the type species, from the Burgess Shale of Canada and the Wheeler and Marjum Formations of the United States,[4] and Peytoia infercambriensis from the Zawiszyn Formation of Poland.[1] Another species of Peytoia may be present in the Burgess Shale, represented by a single frontal appendage from the Tulip Beds locality.[5] A specimen regarded as Peytoia cf. nathorsti is known from the Balang Formation of China.[6]
The history of Peytoia is entangled with that of "Laggania" and Anomalocaris: all three were initially identified as isolated body parts and only later discovered to belong to one type of animal. This was due in part to their makeup of a mixture of mineralized and unmineralized body parts; the oral cone (mouth) and frontal appendage were considerably harder and more easily fossilized than the delicate body.[7]
The first was a detached frontal appendage of Anomalocaris, described by Joseph Frederick Whiteaves in 1892 as a phyllocarid crustacean, because it resembled the abdomen of that taxon.[7] The first fossilized oral cone was discovered by Charles Doolittle Walcott, who mistook it for a jellyfish and placed it in the genus Peytoia. In the same paper, Walcott described a poorly-preserved body specimen as Laggania; he interpreted it as a holothurian (sea cucumber). In 1978, Simon Conway Morris noted that the mouthparts of Laggania were identical to Peytoia, but interpreted this as indicating that Laggania was a composite fossil of Peytoia and the sponge Corralio undulata.[8] Later, while clearing what he thought was an unrelated specimen, Harry B. Whittington removed a layer of covering stone to discover the unequivocally connected arm thought to be a phyllocarid abdomen and the oral cone thought to be a jellyfish.[9][7] Whittington linked the two species, but it took several more years for researchers to realize that the continuously juxtaposed Peytoia, Laggania and frontal appendage represented one enormous creature.[7] Laggania and Peytoia were named in the same publication, but Conway Morris selected Peytoia as the valid name in 1978, which makes it the valid name according to International Commission on Zoological Nomenclature rules.[8][10]
