The genus Branchamphinome Hartman, 1967 is a moderately understood genus of Amphinomidae that differs morphologically from most other genera in the form of its chevron-shaped caruncle and the presence of branchiae from chaetiger 1. Branchamphinome is presently represented by two deep-water species: B. antarctica, described from the Southern Ocean and B. islandica, from Iceland. We describe a new species of Branchamphinome from shallow South-west Atlantic waters, coast of Brazil. The new taxon revealed the surprising presence of notopodial hooks in chaetiger 1, which was subsequently also found to be present in the lectotype of B. antarctica. Both the genus and Hartman's species are emended to include this morphological feature. Historically, the presence of notopodial hooks has long been considered a diagnostic character for the genus Paramphinome, particularly when distinguishing Paramphinome from Linopherus. Branchamphinome tropicalis sp. nov. was found inhabiting sand sediments at depths of 150 m and temperatures of 16–20°C. Branchamphinome tropicalis sp. nov. differs from its congeners by its characteristic and highly developed pigmentation pattern, shape of the caruncle, branchiae and disposition of prostomial eyes. This is the first report of this genus from shallow tropical waters.

Lacydonia Marion & Bobretzky in Marion, 1874 is the only known genus in Lacydoniidae Bergström, 1914, which is composed of small polychaetes scarcely sampled. Studies on the biology and ecology of this group are rare and most species descriptions are based on one or a few specimens. There are 13 nominal species from different parts of the world. We revise herein the morphological characters used for species description on the basis of a lacydoniid assemblage collected in Campos Basin, Southern Brazil. Material was obtained in two sampling campaigns during the Project Habitats/Petrobras – Heterogeneidade Ambiental da Bacia de Campos, coordinated by CENPES/Petrobras. Lacydoniids were collected from the continental shelf, canyons and slope, at depths from 25 to 2500 m. This polychaete family is recorded for the first time in Brazilian waters, three new species are described and all others are new records to the South Atlantic. The new species are Lacydonia anapaulae sp. nov., L. brasiliensis sp. nov. and L. jacki sp. nov. Newly recorded species are L. cirrata (Hartman & Fauchald, 1971), L. laureci Laubier, 1975, L. miranda Marion & Bobretzky in Marion, 1874, L. oculata (Hartman, 1967) and L. cf. papillata Uschakov, 1958. An updated key to all described species of Lacydonia is included.

Newtoniellinae is a worldwide marine group of cold-water, deep-sea species, comprising the genera Cerithiella, Paramendax and Trituba. Prior to this study, the subfamily was represented in Brazil by four species of Cerithiella. The present contribution adds new Brazilian records of two of these species, Cerithiella amblytera and Cerithiella enode, in addition to new records of two species previously known only from Cuba and the south-eastern USA, respectively: Cerithiella sigsbeana comb. nov. and Cerithiella producta. Two new species of Cerithiella from Brazil are described: Cerithiella atali sp. nov. has a pointed protoconch identical to the species described in the previously synonymized genus Stilus; Cerithiella candela sp. nov. has the teleoconch very similar to Cerithiella pernambucoensis, but is differentiated by the protoconch morphology. Also, a new species of Trituba is described, Trituba anubis sp. nov., which is the second species of this genus recorded for the western Atlantic. Eumetula axicostulata comb. nov. and Eumetula vitrea comb. nov., both from the western Atlantic but not recorded from Brazil, are transferred from the genus Cerithiella. This study increases from four to nine the number of known species of Newtoniellinae from Brazil.

Four new species of the genus Desmodora are described from the South Atlantic off the south-eastern coast of the State of Rio de Janeiro, Brazil. Desmodora porosum sp. nov. is characterized by sexual dimorphism in the shape of the amphids, which are closed loop-shaped in males, and multispiral amphids in females. A case of intersexuality was found in the species, with a functional female gonad. Desmodora profundum sp. nov. is characterized by filiform spicules with a capitulum, buccal cavity with one dorsal and one small ventral tooth, tail cylindrical with a terminal spinneret, and wider rings in the neck region than on the rest of the body. Desmodora veronicae sp. nov. possesses cryptospiral amphids, a buccal cavity with one dorsal tooth and two smaller ventral teeth, 14 tubular pre-cloacal supplements, two ventral cuticular protruberances on the tail, and curved spicules with a capitulum and velum. Desmodora curvatum sp. nov. has the cuticle finely striated, without somatic setae, multispiral amphids, and a gubernaculum without apophysis, curved dorsally with the tip directed toward the end of the body.

Paralacydoniids are a small group of burrowing polychaetes, with adults reaching ~10 cm in length. The prostomium is subconical, distally bearing two pairs of frontal appendages; the pharynx is eversible and distally papillate and jaws are absent. The parapodia are biramous, except the first segment which is uniramous. Both rami are widely separated, with long, flattened pre- and post-chaetal lobes, interramal cilia and short digitiform dorsal and ventral cirri. The notochaetae are simple, and the neurochaetae are compound spiniger. The posterior end bears a pair of long cirri. A single species, Paralacydonia paradoxa, has been considered valid. Two other named taxa, Paralacydonia weberi and Paralacydonia mortenseni, are usually considered synonyms of P. paradoxa, although a revision has not been undertaken. Paralacydoniids were collected during the Habitats Project–Campos Basin Environmental Heterogeneity coordinated by CENPES/PETROBRAS, of which the first campaign was held in June–July 2008 and the second campaign in January–February 2009. In all, 289 specimens were observed under the light microscope, and some by means of scanning electron microscopy. The paralacydoniids, collected at depths between 380 and 2514 m, were 0.4 to 19 mm in total length, the largest with 74 chaetigers; the size is related to the number of chaetigers.