Two new species of capitellid polychaetes from the Gulf of Mexico and Atlantic Ocean are described:
Mastobranchus variabilis and
Peresiella spathulata. Emended diagnoses for these genera are proposed. Two species currently assigned to
Mastobranchus,
M. dollfusi Fauvel, 1936, and
M. indicus Southern, 1921, are considered incertae sedis. Keys to the species of
Mastobranchus Eisig, 1887, and
Peresiella Harmelin, 1968, are presented.