Two new species are described from the Patagonia coast of Argentina, South Atlantic, and written keys to both genera are given. Chaetonema patagonica sp. nov. can most easily be differentiated from the other four species of the genus by the amphid shape and by the absence of a precloacal organ. Admirandus sanjuliensis sp. nov. is characterized by position of the Demanian pores, one preanal and two postanal, the configuration of pre- and postcloacal papillae and setae and by having the shortest stoma in the genus.

Patagonema iubatum gen. nov. sp. nov. is described from a sandy beach at Playa Pozo, Golfo Nuevo, Argentina. It resembles Oncholaimidae (Nematoda: Enoplida) and it is characterized by a buccal cavity comprising a combination of three teeth and three mandibular ridges with small teeth. The new genus is also characterized by the presence of papillose pre-cloacal supplements, cephalated spicula and a gubernaculum with dorsal apophysis and lateral piece, and a new demanian system configuration. Patagonema iubatum sp. nov. has 9–11 papillae-like pre-cloacal supplements, short and cephalated spicula and a gubernaculum with dorsal apophysis and pointed lateral piece. Its position inside Oncholaimidae is discussed.