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

A new species of the genus Thalassogenus Andrassy, 1973 is described and dedicated to the memory of Prof. Dr. M. Brzeski. It was extracted from Selaginella sp., La Paz Falls, Costa Rica. The main diagnostic feature is the long tail (108-178 mum, c' = 2.6-4.3); also body length tends to be greater than 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 presence of an ocellus suggests that species of this genus are recent immigrants of freshwater.