Abstract
Three new species of the Molgolaimus (Nematoda: Desmodoridae) are described from sample sediments collected in the South Atlantic, along the continental shelf break of Northeastern Brazil. This is the first time that new species of Molgolaimus have been described from sample sediments collected in the Brazilian coast. Molgolaimus sigmoides sp. nov. is characterized by four small cephalic sensillae, a buccal cavity with three small teeth, S-shaped spicules and gubernaculum with dorsal-caudal apophysis. Molgolaimus paralongispiculum sp. nov. possesses four setiform cephalic sensillae, a buccal cavity with three teeth, thin and elongated spicules and gubernaculum with anteriorly oriented apophysis. Molgolaimus brevispiculum sp. nov. is characterized by its possession of four setiform cephalic sensillae, an unarmed buccal cavity, short spicules and absent gubernaculum. We propose to amend the diagnosis of the genus, redistribute Molgolaimus species into subgroups 1b(1) and 1b(2), and to rearrange the order of presentation of subgroups 4a and 4b.