Penicillidae (Watering pot clams)

Watering Pots (families Clavagellidae and Penicillidae) are bivalve mollusks that make unusual shells. In their early life stages, they look like a tiny clam (middle right photo, indicated by a thin black line). At one point in their growth, however, their shell-making skills “shift” radically, and the bivalve starts manufacturing a shelly tube. The early, small bivalve shell stays behind, embedded onto the outer surface of the tube. Watering pots live buried in soft mud, and get their name from the sieve-like structure at the bottom of their tube