Six species of thelastomatid nematodes belonging to 6 different genera were collected from the peppered cockroach Archimandrita tesselata Rehn, 1903, at the Area de Conservación Guanacaste, Costa Rica, from 2003 to 2006. We describe Aoruroides costaricensis n. sp. This species differs from the other described members of the genus in female cephalic morphology and male papillae arrangement as well as having different morphological dimensions including a shorter female esophagus than that of Aoruroides philippinensis (Chitwood and Chitwood, 1933) and Aoruroides queenslandensis Jex, Cribb, and Schneider, 2004, longer esophageal corpus and isthmus than in Aoruroides legionarius Kloss, 1966, and a much shorter male tail than that of A. legionarius Kloss, 1966. The 5 additional species recovered included Buzionema validum, Protrelleta floridana, Cranifera cranifera, Hammerschmidtiella diesingi, and an unidentified species from the family Thelastomatidae. These species are redescribed using light and scanning electron microscopy and constitute new host and geographical records.