Relict Megascolecidae and exclusion of Lumbricidae from basalt-derived soils in southern California

Estimates of the composition and density of earthworm species were made from nine basalt-derived soil (BDS) areas and from surrounding non-basalt-derived soils (NBS) in southern California. Soils from selected sites were analysed for various chemical constituents. Eight BDS and a few of the NBS sites contained Diplocardia californiana James (Megascolecidae), a species widespread throughout southern California. D. woodi James, a relict species, was collected from only two of the BDS sites. Despite their common occurrence in the area, Lumbricidae were absent from the BDS sites, implying that some soil factors may be involved in their exclusion. Total soil iron content was about four times higher in the BDSs than in the NBSs. No other soil constituent measured showed as much difference.