Phylum Phoronida

Major Attributes:
  1. Bilaterally symmetrical; lophophore at anterior end.
  2. Pelagic larvae.
  3. Small sedentary worms which exist in chitinous tubes.
  4. Exist on benthic substrate; suspension feeders.
  5. Protostomate; even still, the cleavage of the eggs is radial and indeterminate.
  6. Tripartite body plan, each region has its own separate body cavity "ologomeric".
  7. Vascular system with haemoglobin and two excretory organs.
  8. Silmutaneous hermaphrodites, occasional gonochoristic species.

Phoronids, commonly called horseshoe worms, are sessile organisms that live exclusively in marine environments. They are attached to a substrate and live in a chitin-like tube that is made from secretions in their earlier strages of life. These tubes eventually become decorated with debris and gives the horseshoe worm camouflage. The body is composed of three regions. The first region of the tripartite body is the prosome which is small and overhangs the mouth. The second region, the mesosome, is small but contains the large lophophore, the mouth, and the mesocoel which is used as the lophophoral hydraulic system. The last and largest is the metasome which contains the other body organs and the anus. Most phoronids are hermaphroditic and their sex cells exit through the excretory ducts. The egg hatches into a pelagic larva called an actinotrocha. The larva already has a gut and tentacles present. It then settles to the bottom where it starts to secrete its chitin-like tube.

Some Interesting Facts: