The sibling species of Capitella capitata are globally known for their tolerance to disturbed habitats and the C. capitata complex is often used as an ecological indicator. A recent re-description proposed that C. capitata, originally described in Greenland is restricted to the Artic and Subarctic regions. Given their ecological relevance, we conducted a morphological and molecular analyses based on mtDNA sequences to investigate the diversity and distribution of the C. capitata complex along the Brazilian coast. Our morphological and molecular data were congruent and revealed the existence of four new species distinct from C. capitata, collected from the type locality. This study is the first characterization of the biodiversity and distribution of Capitella species made along the Brazilian coast and yielded a set of morphological characters corroborated by the mtDNA sequences for species identification. Our results increase the biodiversity of the genus along the Brazilian coast by describing four new species (Capitella aracaensis sp. n., Capitella biota sp. n., Capitella neoaciculata sp. n. and Capitella nonatoi sp. n.). One species was collected from only one sampling site, while the others are distributed along the coast.

The presence of two species within the Eurythoe complanata complex in the Mediterranean Sea is reported, as well as their geographical distributions. One specie

Pseudoscalibregma Ashworth, 1901 is a small genus of the family Scalibregmatidae Malmgren, 1867. Currently, a total of eight valid species are accepted. Of these, the majority are found at great depths. This work contains the first report of Pseudoscalibregma to the Brazilian coast, with the description of three new species: Pseuscalibregma ermindae sp. nov., P. magalhaesi sp. nov. and P. parapari sp. nov. The material was sampled from the Brazilian southeast region, on Campos and Santos sedimentary basins, during scientific expeditions called “Santos Project—Santos Basin Environmental Characterization” and “Ambes Project—Espírito Santo Basin Assessment Project”, both coordinated by PETROBRAS/CENPES. We also include an identification key to Pseudoscalibregma species.