Georgette Douwma / Southern horseshoe worm or Phoronids tubeworm (Phoronis australis). Ambon, Indonesia.

Georgette Douwma / Southern horseshoe worm or Phoronids tubeworm (Phoronis australis). Ambon, Indonesia.

Alex Mustard / Filter feeding appendages of a Yellow california horseshoe worm (Phoronopsis californica) extending from the sand. Bitung, North Sulawesi, Indonesia. Lembeh Strait, Molucca Sea.

Georgette Douwma / Southern horseshoe worm (Phoronis australis). Lembeh Strait, North Sulawesi, Indonesia.

Fred Bavendam / Tube-dwelling Anemone (Cerianthus sp) with Feather Duster Worms (Sabellastarte sp), Bali, Indonesia

Constantinos Petrinos / Star horseshoe worm {Pomatostegus stellatus} on coral, Grand Cayman, Caribbean

Juergen Freund / Star horseshoe worm / fanworm (Pomatostegus stellatus) Caribbean

Fred Bavendam / Horseshoe Worm (Phoronis australis) living on the column of a Tube-dwelling Anemone (Cerianthus sp), Bali, Indonesia

Chris Newbert / Star Horseshoe Worm (Pomatostegus stellatus) growing in Hump Coral (Porites sp) 40 feet deep, Solomon Islands

Chris Newbert / Star Horseshoe Worm (Pomatostegus stellatus) in sponge, Roatan Island, Honduras

Solvin Zankl / Portrait of Horseshoe worm (Phoronis muelleri) larva swimming, Raunefjorden near Bergen, Norway.