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