Two new species of Microlaimidae (Nematoda: Microlaimida) from the Continental Shelf off Northeastern Brazil (Atlantic Ocean) with emended diagnosis and dichotomous key

New species of the genera <i>Spirobolbolaimus</i> and <i>Ixonema</i> (Nematoda: Microlaimidae) have been found in sediment samples collected in the South Atlantic, along the Continental Shelf break off Northeastern Brazil. Different to other <i>Spirobolbolaimus</i> species, <i>S. pernambucanus</i> <b>sp. nov.</b> possesses six outer labial setae and four cephalic setae with approximately the same length. <i>Ixonema gracieleae</i> <b>sp. nov.</b> differs from other species of <i>Ixonema</i> in having somatic setae on peduncles. This is the first time that new species of these taxa have been described for the Brazilian coast. An amendment of the diagnosis and a dichotomous key are proposed for both genera.