Another one would be the Medicinal Leech (Hirudo medicinalis) and
although not as well studied genetically as the nematode C elegans, it
is a much more active organism, and its motor systems is very
interesting from that standpoint.
Here are some references:
Brodfuehrer & Thorogood (2001) Identified neurons and leech swimming
behavior, Prog Neurobiol. vol 63(4): pg 371-81
von Bernhardi & Muller (1995) Repair of the central nervous system:
lessons from lesions in leeches, J Neurobiol. vol 27(3): pg 353-66
Sahley (1995) What we have learned from the study of learning in the
leech, J Neurobiol. vol 27(3): pg 434-45
Brodfuehrer et al (1995) Neuronal control of leech swimming.
J Neurobiol. vol 27(3): pg 403-18
Or a website at