The Helcionellids are Cambrian fossils interpreted as early (or stem group) molluscs. They are similar in shape to the end of a jester's shoe, and commonly bear ridges encircling their circumference. They first appear in the late Nemakit-Daldynian (lower Early Cambrian), and are a constituent of the small shelly fauna (SSF). Larger individuals, reaching centimeters in diameter, have also been found. They would have had a tube extending from the concave side of their shell, which would have been involved in circulating water in and out of the water cavity.