Wiwaxia

Wiwaxia corrugata was a bizarre, slug-like animal that crawled along the seafloor during the Middle Cambrian period, a time of explosive evolutionary experimentation. Its fossils, most famously found in the Burgess Shale of Canada, reveal a creature unlike any living today. The soft, bilaterally symmetrical body was completely covered by an impressive coat of armor, consisting of small, overlapping, leaf-like plates called sclerites. This protective covering gave it a corrugated or chainmail-like appearance. Protruding from its back were two rows of long, sharp, carbonaceous spines, which likely served as a formidable defense against predators such as Anomalocaris. Wiwaxia was a benthic organism, meaning it lived on the ocean bottom. It possessed a simple, jaw-like feeding apparatus with two or three rows of backward-pointing teeth, similar to a mollusc's radula. This structure suggests it was a detritivore or herbivore, scraping microbial mats and organic debris from the substrate. Ranging from just a few millimeters to over five centimeters in length, Wiwaxia's unique combination of features has made its evolutionary placement a subject of intense debate. While it shares characteristics with both annelid worms and molluscs, many paleontologists now consider it to be an early, stem-group mollusc, offering a fascinating glimpse into the early diversification of major animal groups.