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I love worm composting (I use red wiggler worms), but wondering how similar or different the Caenorhabditis elegans and Eisenia fetida are?

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It's possible that the gardening stack exchange might provide better answers if you're interested in their differences in regards to composting. –  Oreotrephes Aug 22 '13 at 6:20
    
@Mys-721tx's answer (excellent, by the way!) is the type of response you'll get here. –  Oreotrephes Aug 22 '13 at 7:40
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Caenorhabditis elegans is a nematode. Eisenia fetida is an annelid. They both are lophotrochozoans (more specifically, trochozoans).

Time of Divergence

According to Michael Lynch, there are about 41 amino-acid substitutions per site between Annelida and Nematoda. According to Lynch's data, I estimated that this difference is roughly equal 100 million years.

Therefore, assuming the rate of molecular evolution was constant, their common ancestors lived about 100 million years ago.

Difference on Anatomy

Nematodes have pseudocoelom while annelids have eucoelom. Therefore nematodes do not have a vascular blood system. However, annelids do have one. Nematodes also lack a layer of circular muscle, which annelids have. This layer of muscle allows annelids to move by shorten and elongate their bodies.

C. elegans in particular does not have a female gender. There are only male worms and hermaphrodite worms. Only the male can fertilize other worms.

E. fetida is hermaphroditic and two of them can fertilize each other.

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The time of divergence within the nematodes is already estimated to be >500 million years timetree.org/pdf/Blaxter2009Chap28.pdf -- so the divergence of annelids and annelids must be even earlier –  Michael Kuhn Aug 22 '13 at 12:41
    
What does "there are about 41 amino-acid substitutions per site" mean? –  Jack Aidley Aug 22 '13 at 13:51
    
@MichaelKuhn It's probably true. Also notice that the Lynch paper was published in 1997, the sequence data he used might simply be not good enough. –  Mys_721tx Aug 22 '13 at 15:44
    
@JackAidley Lynch compared 10 proteins encoded by mitochondrial genes between organisms in 12 phyla. The "substations per site" are the differences in protein sequences coded by homologous genes in two compared organisms. –  Mys_721tx Aug 22 '13 at 15:54
    
@Mys_721tx: I don't see how you can have 41 amino-acid substitutions at a single site between two homologous genes. Surely you can have at most one substitution per site on each gene? –  Jack Aidley Aug 22 '13 at 15:58
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