Pohlsepia mazonensis is a species of fossil organism with unknown affinity. Although it was originally identified as an extinct cephalopod, later studies denied that interpretation. The species is known from a single exceptionally preserved fossil discovered in the late Carboniferous (Pennsylvanian) Francis Creek Shale (Mazon Creek fossil beds) of the Carbondale Formation, north-east Illinois, United States. Pohlsepia mazonensis is named after its discoverer, James Pohl, and the type locality, Mazon Creek. Its habitat was the shallows seawards of a major river delta in what at that time was an inland ocean between the Midwest and the Appalachians. In its initial description, it was considered to be the oldest known octopus, but later studies have considered this classification dubious. In 2022, it was even shown that it may not be a mollusk. The type specimen is reposited at the Field Museum of Natural History in Chicago, Illinois. Fossil The Pohlsepia mazonensis fossil found by James Pohl is the only known example of the species. Most notably, the fossil has ten arms. The extra two arms are shorter, while the other eight are similar in length. The wide fossil is “sack-shaped” with indistinct features including a poorly defined head. While it is unclear, one of these features could be an ink sac. The fossil lacks arm hooks and suckers and all of these factors combine to make the assigning of the order Cirroctopoda controversial. Etymology Genus name Pohlsepia is came from its discoverer James Pohl. He is the son of Joe Pohl and together they have collected fossils in the Mazon Creek area. Originally from Wisconsin and Minnesota, Pohl is a native Midwesterner. He and his father have donated their fossils to museums in the area, including Pohlsepia mazonensis to the Field Museum. Classification In 2000, Joanne Kluessendorf assigned Pohlsepia mazonensis to the order Cirroctopoda. Many other researchers disagreed, citing the lack of internal structure. The possible evidence of fins and the huge time difference between the Pohlsepia mazonensis fossil and first confirmed cirrate octopus fossils is problematic. However, the species can be classified as an octopod. Despite having ten arms, the fact that the fossil has an indistinct head, sac like body and similar fins to cirrate octopods gives enough evidence to classify Pohlsepia mazonensis in the order Cirroctopoda. When looking at the groups Teudopsidae, Trachyteuthididae, the Vampyromorpha, cirrate octopods, incirrate octopods and the fossil Loligosepiina, the describing authors proposed Pohlsepia