2 NEW SPECIES OF THE EARTHWORM GENUS LAVELLODRILUS (OLIGOCHAETA, ACANTHODRILINI) FROM TROPICAL MEXICAN RAIN-FORESTS

Lavellodrilus ilkus and L. bonampakensis are described from two Mexican tropical rain forests. Some ecological observations are also discussed. Despite the presence of an intestinal gizzard, these species are placed in the genus Lavellodrilus (where this character is absent) because they present sexual characters diagnostic of this genus and by the close association of this feature with a certain ecological niche. The adaptive nature of intestinal gizzards in non-moniligastid genera is discussed in terms of: their repeated appearence, Bouche's hypothesis of functional constraints and the suggested adaptive function. It is proposed that in the new species described seasonality of tropical rain forest environment may have represented the constraint which selected the displacement of the gizzard.