This is the third guide in a series aimed to help in the identification of northern European samples through the NationalMarine Biological Analytical Quality Control (NMBAQC) Scheme. A review is presented of general morphology andbiology of one of the most common groups in marine and estuarine communities worldwide, spionid polychaetes(Annelida: Spionidae). An identification key to 20 genera and a list of 80 species likely to occur in waters around Britainand Ireland are provided based on the taxonomic literature, collection records and the author’s examination of various collections. The names are updated but some records need verification.

Nineteen species in seven genera of spionid polychaetes are described and illustrated based on new material collected from the intertidal and shallow waters around the Lizard Island Group, northern Great Barrier Reef. Only one of these species had been previously reported from the Reef. Six species are described as new to science, and the taxonomy of seven species should be clarified in the future. Prionospio sensu lato is the most diverse group with 11 species identified in the present study. One species is identified in each of the genera Dipolydora, Polydorella, Rhynchospio and Tripolydora, and two species are identified in each of the genera Aonides and Pseudopolydora. The fauna of spionid polychaetes of the Great Barrier Reef seems to be more diverse than previously described and more species are expected to be found in the future. An identification key is provided to 16 genera of Spionidae reported from or likely to be found on the Great Barrier Reef.

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.