The Lophophore

The Lophophore is a characteristic feeding organ possessed by three major groups of animals:

The lophophore can most easily be described as a ring of tentacles, but it is often horseshoe-shaped or coiled. Phoronids have their lophophores in plain view, as shown above, but brachiopods like the one below must be opened wide in order to get a good view of their lophophore.

Why do we call these tentacles a lophophore? Because these tentacles have several distinctive characteristics that differentiate them from the tentacles of other animals. First, these tentacles are hollow. Hollow cavities in the bodies of animals (except for the gut) are called coeloms: for all brachiopods, phoronids and bryozoans, the hollow cavity in the lophophore is the second of the three divisions of the coelom in the entire body. Furthermore, the mouth is always located inside the lophophore ring of tentacles, while the anus lies outside the ring. Finally, the lophophore tentacles are covered with cilia in a specific arrangement that are responsible for generating a current of water that flows toward the mouth.

All of these distinctive characters make the lophophore a complex structure. Since it is complex, the likelihood that it evolved independently in three separate groups of animals is low. Therefore, one can form an hypothesis that the last common ancestor of brachiopods, bryozoans and phoronids also had a lophophore. Through this exercise we have suggested that the lophophore is a synapomorphy that groups these three taxa together. This is how evolutionary biologists accomplish the important task of organizing the biological world into systematic groupings.