Home > Invertebrates > Acorn Worms

Phylum Chordata, Subphylum Hemichordata

Acorn Worms

Acorn worms are related to the vertebrates since they possess a notochord but there are no vertebral bones.  There is a collar-like structure at the head which makes them easy to distinguish from other worm phyla.  They are burrowing forms that leave coils of sand at the surface.  A food source for many mollusks and fishes.



Ptychodera flava

Kaneohe Bay, Oahu, 10 feet


Paiko, Oahu, 1 foot

Makua, Oahu, 30 feet


Kaneohe Bay, Oahu, 3 feet


A common buried species on sand flats.  Expels coil of sand as it feeds.  Preyed upon by fishes, cones, and auger shells.  Attains at least 8 inches.  A much larger form occurs in deep water but may not be the same species.  Hawaii, Indian Ocean to the Galapagos.