Two species of Acuaria were collected from passerine birds from the Area de Conservacion Guanacaste, Costa Rica. Acuaria mayori Lent, Freitas and Proenca, 1945, was collected from Myiarchus nuttingi. Specimens from Costa Rica differ from the original description by having a spicule ratio of 1:1.5–1.7 versus 1:1.43–1.47, as well as shorter spicules and female tails. Acuaria wangi n. sp. in Hylophylax naevioides and Gymnopithys leucaspis resembles A. alii, A. crami, A. cyanocitta, A. minuta, A. pattoni, and A. cissae by having cordons extending posteriorly to the anterior portion of the glandular esophagus. The new species differs from A. alii by having 4 pairs of preanal and 6 pairs of postanal papillae rather than 2 pairs of preanal and 7 pairs of postanal papillae, a shorter left spicule, a spicule ratio of 1:1.6–1.8 versus 1:1.1 and in having spicules with blunt rather than pointed distal ends. Acuaria crami and A. minuta differ from A. wangi by having 7 pairs of postanal papillae and spicule ratios of 1:1.6–1.8 versus 1:1.3 in A. crami and 1:1.1 in A. minuta; in addition, A. minuta has spatulate-shaped spicules and a tricupsid-shaped distal end of the right spicule. The new species can be distinguished from A. pattoni by having a longer left spicule and a spicule ratio of 1:1.6–1.8 versus 1:1 and from A. cissae by having a shorter left spicule and a spicule ratio of 1:1.6–1.8 versus 1:2.5–2.7. Acuaria wangi is similar to A. cyanocitta, which has similarly shaped spicules, including a very pointed distal end of the left spicule, but differs in body length, in having shorter spicules, in the arrangement of postanal papillae, and in having smaller eggs.