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Innervation of the lophophore suggests that the phoronid Phoronis ovalis is a link between phoronids and bryozoans
The validity of the Lophophorata as a monophyletic group remains controversial. New data on the
innervation of the lophophore, which is a unique feature of the lophophorates, may help clarify the
status of the Lophophorata and provide new information on the early evolution of the group. In this
paper, the organization of the nervous system of the lophophore is described in adults of the minute
phoronid Phoronis ovalis. The lophophore nervous system includes a dorsal ganglion, a tentacular nerve
ring, an inner ganglion, an inner nerve ring, and six nerves in each tentacle. The inner ganglion and inner
nerve ring, which is associated with sensory cells, are described for the first time in adult phoronids. The
general plan of the nervous system of the lophophore and tentacles is similar in P. ovalis and bryozoans.
These new results suggest the presence of two nerve centers and two nerve rings in the last common
ancestor of phoronids and bryozoans. During evolution, bryozoans may have lost the outer nerve center
and outer nerve ring, whereas phoronids may have lost the inner nerve center and inner nerve ring.
These morphological results evidence the lophophorates are monophyletic.