A new species Spiochaetopterus nonatoi is described from the south-eastern coast of Brazil, the type locality being Flamengo Bight, 6-m depth (23°30′S 45°06′W). This species is distinguishable from already erected species of the same genus by the following characteristics: oculate specimens of large size; maximum segments, 197 (N=15); maximum tube length, 45 cm; maximum body length, 20 cm; orange coloration of the fore part (peristomium and segment 1) and of the ventral shield on segments 6–7; shape of the specialized enlarged cutting seta on A4 with an obliquely truncated distal end; this slightly concave section is heart-shaped and clearly asymmetrical; segments B1 and B2 with one lobe on the neuropodia. This additional description in the genus Spiochaetopterus confirms the limited geographical area of each species in this genus. In spite of the probable ability of planktonic larvae of Spiochaetopterus to disseminate throughout the Atlantic Ocean, the benthic adults of each species cover only a limited geographical area. In particular, the stem species S. costarum loses its cosmopolitan character.