A large number multitentaculate cirratulids have been described worldwide but most are only known through the original descriptions. Type material, voucher and recently collected specimens from Brazil were revisited in order to reveal their true identity and confirm the records of widely distributed species in this region. Six species are described, three of which are new, Cirriformia capixabensis sp. nov., Cirriformia chicoi sp. nov. and Timarete ceciliae sp. nov. COI and 16S sequences were obtained and used for inter-specific comparisons. Timarete caribous is reported from several localities along the Brazilian coast and a new synonym, Cirratulus melanacanthus, is proposed. The species Timarete oculata, originally described from Brazil and lumped into the Timarete filigera species complex, is herein revalidated and redescribed. The occurrence of the species Timarete filigera and Cirriformia tentaculata is not confirmed from the Brazilian coast. Descriptions, illustrations and a key to genera and species are provided.

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.

Here we describe, for the first time, the mitochondrial genome of Spirobranchus giganteus (Annelida: Serpulidae) and compare it with all available annelid mitogenomes. The entire mitogenome has 22,058bp in length and bears 12 protein-coding genes (the ATP8 gene is missing), two rRNA, and 24 tRNA genes. The nucleotide composition and GC-skew are surprisingly different from those reported for other annelids. In addition, the pairwise genetic distances between the mitogenomes of S. giganteus and other annelids are higher than the distances for all annelid taxa analyzed. This result is consistent with a faster rate of mitochondrial sequence evolution in S. giganteus, which may explain the difficulty in obtaining PCR products with the available primers. The mitochondrial gene order of S. giganteus was remarkably different not only from that of the Sedentaria lineage, which includes S. giganteus, but also from the mitochondrial gene order of other major annelid lineages. The mitogenome of S. giganteus has no repetitive motifs despite its long control region (4769bp), but genes are shorter and have a lower AT content than other members of Annelida. Finally, we show that mitochondrial gene order rearrangements can directly correlate to variations in gene length.

Diopatra is the most species-rich genus of Onuphidae with about 60 species. Although 14 species have been reported for Brazil, the cosmopolitan D. cuprea is the most commonly reported from the area, including populations with a large morphological diversity. To better elucidate this species complex, we use morphological and molecular data, and reveal a hidden diversity. Thus, we describe four new species (D. hannelorae sp. nov., D. marinae sp. nov., D. pectiniconicum sp. nov. and D. victoriae sp. nov.) and discuss their geographical and bathymetrical distributions. None of the analysed specimens could be identified as D. cuprea based on available sequences. New taxonomic characters were highlighted, including jaw morphology, which was the determinant factor to differentiate D. marinae from D. victoriae. Phylogenetic analysis indicates three (COI and ND4) or four (concatenated) lineages, because D. marinae was not always reciprocally monophyletic. Sequence-based species delimitation also indicates three to five species, depending on the method used. Inter- and intragroup genetic divergence and haplotype network analysis supported four species. The divergence time among species indicates that Pleistocene sea-level fluctuations and the Vitória–Trindade chain limited the gene flow between northern and southern populations and contributed to the emergence of species, mainly in the case of D. marinae and D. victoriae.

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