Volume 38 (2008) Issue 2 Pages 57-69
The nematode genus Actus belonging to the order Mononchida, an important group of predatory nematodes, is rare in the world. Actus salvadoricus Baqri and Jairajpuri, 1974, which had been described from El Salvador, were found from subtropical forest in the northern part of Okinawa Island, Japan. Its morphological observation is made herein and its phylogenetic position is elucidated based on 18S rDNA sequence. A. salvadoricus collected from Okinawa is characterized by having its buccal cavity with a moderately developed dorsal tooth, vertical subventral plates with a single row of denticles arranged as 3:3 or 3:4 or 2:4 on two plates, distinct excretory pore, elongate-conoid ventrally arcuate tail, with tandem caudal glands and terminal spinneret. Based on the nearly complete 18S rDNA sequence data already known and revealed in this work, phylogenetic trees of Mononchina were constructed using parsimony and maximum likelihood algorithms. The results show that the genus Actus forms a sister group with the species of the genus Mylonchulus in the suborder Mononchina, showing the valid status of its taxonomic group.