Nothobomolochus cresseyi sp. n. (Copepoda: Bomolochidae), a parasite from gills of the engraulid fish Engraulis anchoita Hubbs et Marini (Pisces: Engraulidae) from the coast of Argentina, is described and illustrated. The new species can be distinguished from other species of Nothobomolochus Vervoort, 1962 by the following combination of characters: three modified setae on the base of the antennule similar in length to the plumose setae, the nature of the armature of the third segment of the fourth endopod and the length and width of the thoracic somites 2 to 4 decreasing gradually. The new species represents the first record of this genus for Argentina.
Ichthyofilaria argentinensis Incorvaia, 1999 (Nematoda: Philometridae) is redescribed from type specimens and from parasites collected from the swim bladder of Argentine hakes Merluccius hubbsi Marini, 1933 caught at the Gulf of San Jorge (46°30'S, 66°30'W), Argentine Sea, in July, 1998. Sixteen out of 80 hakes (20%) were found to be parasitised by gravid females of this philometrid. After revision of both these nematodes and type material, the following differences from the original description of the species were observed: (a) cuticle with fine transverse striations, instead of smooth cuticle; (b) presence of cephalic papillae and a pair of amphids; (c) absence of swellings in the oesophagus; (d) oesophageal gland appendix very large and lobulate rather than small and vermiform, and (d) presence of vulva and vagina. The morphological features given in the redescription allow the confirmation of the identity of I. argentinensis as a valid species and to distinguish it from other members of the genus.