A new nematode species, Comephoronema multipapillatum sp. n. (Cystidicolidae), is described from the anterior intestine and caecum of the squirrelfish Holocentrus adscensionis (Osbeck) (Beryciformes: Holocentridae) collected in Angra dos Reis, State of Rio de Janeiro, offshore Brazil. The new species was placed in Comephoronema Layman, 1933 by having an oval oral aperture, four submedian labia, four bilobed submedian sublabia, two narrow lateral pseudolabia and four single cephalic papillae, but mainly by numerous precloacal papillae in males (more than six pairs), in which it differs from species of the otherwise morphologically similar genus Ascarophis van Beneden, 1871. Comephoronema multipapillatum sp. n. can be easily distinguished from other congeners based on the high number of precloacal papillae in males (18 pairs + one unpaired) and also by the bidentate plate structure on the inner margin of pseudolabia, mature eggs with two long filaments on a single pole, body length of male (9.4-11.5 mm) and female (10.2-19.9 mm), left spicule size (222-278 µm) and length ratio of spicules (1 : 2.2-2.8). This is the fifth nominal species of Comephoronema, the first nematode registered parasitizing H. adscensionis and the first species of the genus in the Neotropical part of the Atlantic Ocean.