First three new species of free-living marine nematodes of the <i>Molgolaimus</i> (Nematoda: Desmodoridae) from the continental shelf of the Brazilian coast (Atlantic Ocean)

Three new species of the <i>Molgolaimus</i> (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 <i>Molgolaimus</i> have been described from sample sediments collected in the Brazilian coast. <i>Molgolaimus sigmoides</i> <b>sp. nov.</b> is characterized by four small cephalic sensillae, a buccal cavity with three small teeth, S-shaped spicules and gubernaculum with dorsal-caudal apophysis. <i>Molgolaimus paralongispiculum</i> <b>sp. nov.</b> possesses four setiform cephalic sensillae, a buccal cavity with three teeth, thin and elongated spicules and gubernaculum with anteriorly oriented apophysis. <i>Molgolaimus brevispiculum</i> <b>sp. nov.</b> 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 <i>Molgolaimus</i> species into subgroups 1b₁ and 1b₂, and to rearrange the order of presentation of subgroups 4a and 4b.