  A new exactly solvable one-dimensional spin-3/2 Heisenberg model with
SO(5)-invariance is proposed. The eigenvalues and Bethe ansatz equations of the
model are obtained by using the nested algebraic Bethe ansatz approach. Several
exotic elementary excitations in the antiferromagnetic region such as neutral
spinon with zero spin, heavy spinon with spin-3/2 and dressed spinon with
spin-1/2 are found.
