Ice-cream coneworms

Like methodical stonemasons, the resourceful ice-cream coneworms (Family Pectinariidae) build tubes from single grains of sand carefully bonded together with proteinaceous glue. Sand grains range from very fine to coarse, but the size of the grains increases as the worm grows, making tube composition alone insufficient for distinguishing species. The shape of the tube—straight or gently curved—remains unchanged with growth, but shape is not always reliable for identification if the posterior end is broken off. Generally, detailed examination of chaetae (bristles) is required. Ice-cream coneworms probably freely spawn their gametes into the seawater, where fertilization occurs. Curiously, the larvae are so predisposed to start digging that after several weeks in the plankton they metamorphose and secrete a larval tube while still floating in the water column! Soon thereafter they settle to the bottom to assume an adult existence.