The distribution and composition of the ridge crest fauna of Cleft segment, southern Juan de Fuca Ridge, are examined in the context of geological settings. The concept that faunal characteristics should reflect lava age and morphology was tested with information from vent animal collections and from photographs of nonvent fauna. Numbers of both vent and nonvent species are low compared to the other sites in the region. The young age of the segment, relative eruptive instability, terminal position on the ridge, and current patterns may influence species accumulation. Recently eruptive lavas, 2 to 6 years old, were already colonized by several vent species but only two sessile nonvent animals; search and recruitment capabilities of vent species appear to be highly developed. Lava age and morphology do not appear responsible for observed differences in species composition from vent fauna between samples. In contrast, nonvent assemblages showed abundances that reflect lava ages, although the basalt morphology complicated the pattern. That gross geological setting does not explain vent faunal characteristics suggests that factors such as water chemistry and reproductive behavior need closer investigation.