If you are so inclined, this mystery could be "evidence" against evolution: if scientists can't classify a 525 million-year-old fossil (annelid? arthropod? mollusc? something else?) then why is there any reason to think it "evolved" at all, rather than having been "created" sui generis and sent on its merry way, snurfling along the Cambrian sea floor.
Regardless, there is an interesting scientific puzzle presented by Vetustodermis planus, the 2-4 inch fossil found in Anning, China, which had a flattened body, horizontal fins, and well developed senses including a pair of eyes on stalks.
According to a study published in Proceedings of the Royal Society B, the creature seems closest to molluscs, primarily because it had a slug-like flat foot, but it's not a flush fit there, either.
"Phyla are defined by an organism having a set of features called characters, and currently there are no animals that we know of which contain the set of characters that Vetustodermis has," co-author David Bottjer, of the University of Southern California, told the BBC. "The phylum with which it shares the most characters is the Mollusca, but squeezing Vetustodermis into the mollusca is a somewhat messy job."
"We have always been intrigued by the many molluscan features of these fossils," he continued, "but in the great menagerie of organisms that have inhabited Earth through life's long history, we may come to conclude that Vetustodermis indeed represents a new phylum."
Jonathan Todd, a palaeontologist from the Natural History Museum, London, is reluctant to cavalierly create a whole new phylum. "Some scientists have thought that there were so many distinct phyla in the Cambrian. They came to that conclusion because they were not thinking in the phylogenetic sense, they were thinking 'hey, that is a unique set of features - it must be a distinct phylum'," he sniffed.
"We don't really know the phylo-genetic relationships between the extant phyla," he said. "Molecular genetics has only gone so far. But recent phyla have got to connect somehow. These fossils really offer the opportunity to tie together recent phyla."
So Todd is a "pusher" and Bottjer is a "puller" when it comes to creating a new phylum for the little suck-footed fella, but at least neither accused the other of blasphemy.