Three species of Bunonematoidea, Pterygorhabditis panoplus, Rhodolaimus arboreus sp. n. and Rhodolaimus dimorphus are described and illustrated on the basis of material collected in Costa Rica. SEM studies and details of the labial region structure in R panoplus and R. arboreus sp. n. are given. Rhodolaimus arboreus sp. n. is characterised by the 0.2-0.25 mm long body, left body side with five parallel cuticular ridges, right body side with two parallel rows of tubercles, the anteriormost pair of which are almost fused, 28-33.5 mum long spicules, cylindrical gubernaculum, bursa developed on left body side and seven pairs of caudal papillae.