The deep sea is teeming with species that have never known sunlight, according to a news release from the Census of Marine Life, a systematic investigation of life on the ocean floor. The deepest ocean floor was once thought to be too barren, cold, dark and pressurized for life to flourish there. Wrong! Actually, "The abyssal fauna is so rich in species diversity and so poorly described that collecting a known species is an anomaly," says Dr. David Billett of UK’s National Oceanography Centre.
Some of this life depends on food from higher levels that settles to the depths, but other species there survive entirely on inorganic chemicals. We suspect that species in the latter category could also survive in the deep ocean on Europa, for example.
http://coml.org/embargo/emb_bs09/CoML_Beyond_Sunlight_11.17.2009.pdf