First record of Trochochaeta japonica (Annelida: Spionidae) in Brazil with identification key to species of the genus.

Polychaetes of the spionid genus Trochochaeta occur mainly in the northern hemisphere, including North and Central America. In South America, they have been reported only from the northeast region of Brazil - Sergipe and Paraíba - despite numerous biological investigations around the continent. In 2006, a dense population (up to 7000 individuals per square meter) of Trochochaeta was discovered in the estuary of Santos, São Paulo, Brazil, hosting the busiest container sea port in Latin America, and in 2008, one Trochochaeta specimen was found in Camamu Bay, Bahia. We identify these worms as Trochochaeta japonica Imajima, 1989 and describe and illustrate their morphology. This is the first record of the species from outside of its type locality in Honshu, Japan. It might have been introduced to the estuary of Santos as larvae in ballast water of ocean-going vessels. We review the systematics of Trochochaeta and provide an identification key to 12 currently recognized species.