A new species of the genus Thalassogenus Andrassy, 1973 and the systematicpositiont of the genus (Nematoda : Oncholaimina)

A new species of the genus Thalassogenus Andrassy, 1973 is described and de dicated to the memory of Prof. Dr. M. Brzeski. It was extracted from Selagi nella sp., La Paz Falls, Costa Rica. The main diagnostic feature is the lon g tail (108-178 mum, c' = 2.6-4.3); also body length tends to be greater th an in the other species (2.3-3.2 mm vs 1.7-2.5). Opinions vary with regard to the systematic position of the genus; Oncholaimina (Pelagonematidae) or Mononchina. We show that it belongs to Oncholaimina, where it represents a separate family. The genus is now known from four widely spaced regions in the tropics - India, New Guinea, Samoa Islands and Central America. The pre sence of an ocellus suggests that species of this genus are recent immigran ts of freshwater.