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Hatschek 1888


Phylum Phoronida
Family Phoronidae
Genus Phoronis


  • 0.6 mm to over 2.5 mm.


  • One of the two genera of the horseshoe worm family (Phoronidae), Actinotrocha larva are one of the largest marine larval forms.

Distinguishing characteristics

  • Bullet-shaped.
  • Anterior umbrella-like body region (pre-oral hood).
  • Middle body region is the collar.
  • Ring of tentacles along posterior boundary.
  • U-shaped digestive tract - the gut loops and ends close to the mouth instead of passing straight through the body.
  • Soft body.


  • Found in most oceans and seas globally, except for polar seas.
  • Phoronids are mainly found from 0 to 70 m depth.


  • Metamorphosis is rapid and unique, lasts 15-30 minutes and leads to the slender actinotroch larva form (Larink and Westheide 2006).
  • Several to many weeks feeding in plankton (Johnson and Zimmer 2002).