ИСТИНА

Altogether 17 nematode species of nearly one thousand collected specimens have been registered in six hydrothermal sites along the Mid-Atlantic Ridge. Samples were washout taken from aggregations of mussels Bathymodiolus spp. and debris accumulated in rock cracks. The most common species are Prochaetosoma sp. n., Paracanthonchus sp. n., Oncholaimus sp., Desmodora sp., Thalassomonhystera vandoverae, Prochromadora sp. n., Leptolaimus sp. n., Microlaimus sp., in sequence of decrease the percentage in community. Nematofauna of the Mid-Atlantic Ridge hydrotherms is characterized by features: 1) species diversity is low in comparison with both of shelf and adjacent deepsea bed; 2) In the generic composition, nematode communities of the deep-sea hydrothermal vent biotopes are more similar to those of shallow water sediments than to those of the adjacent abyssal fine sediments around the hydrotherms; 3) in the average body size, nematode communities of the deep-sea hydrothermal areas are more similar to those of shelf sediments than to those of the adjacent abyssal plains around the hydrotherms; 4) most deep-sea hydrothermal nematode species possess enlarged buccal cavity with armature (feeding on larger particles) while most species of adjacent abyssal plains are characterized by narrow unarmed buccal cavity (feeding on smaller bacteria-sized particles); 5) distinct food content within guts in most hydrothermal nematode specimens (intensive feeding) while guts of most abyssal specimens are empty; 6) most deep-sea hydrothermal nematode females contain ripe eggs in their uteri (high rate of reproduction) while the uteri of most abyssal plain females are empty. 7) contrary to that of mega- and macrofauna, endemism of nematofauna of the deep-sea hydrothermal vent biotopes is comparatively low and does not exceed the species level. The project is supported by the grant RFBR 12-04-00781a. Keywords: Nematoda, hydrothermals of Mid-Atlantic Ridge, feeding, reproduction.