The aim of the present study is mainly to publish the presence of a rich and flourishing annelid fauna in the Gulf of Mexico. Keys and illustrations together with the bibliographic citations may permit a fairly complete and accurate identification of the annelids to be encountered in littoral zones. The collections upon which this study was based come largely from intertidal or shallow seas; only a few are from deeper waters. This investigation has disclosed the existence of a vast, diversified, possibly highly endemic fauna in this area. The few deeper water species that have been reported show affinities with those known also from the West Indies and the tropical Atlantic Ocean.
One hundred fifty-eight species in 110 genera and 36 families of marine annelids are recorded, most of them for the first time from the Gulf of Mexico. There are 15 new species or subspecies, one new name and one new genus. These are listed by family.