Helcionellida

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.

These resemble limpets, with the peak of the shell distinctively curved to form a shape identical to the helcionellids known from the SSF assemblages. Since molluscs grow by adding material to the opening of the shell, it appears that the helcionellids of the SSF are juvenile molluscs, which continued to grow into large limpet-like creatures typical of early Cambrian molluscs.

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.