the legs driven by the ancestors of the Giant Fibers. This behavior was probably similar to the escape system found in a mantis shrimp called Squilla that diverged from the crayfish lineage very early on. It is likely that this mechanism was replaced by the tail flip since the wide surface area of the tail made this behavior more selectively advantageous. This most likely occurred when the ancestral flexor motor neurons in each segment formed connections with one of these limb motor neurons. The Squilla mechanism seems to be similar to this ancestral state because a large diameter axon in the dorsal nerve chord facilitates limb promoter motor neurons. This seems to match the ancestral condition, but it is not known for sure whether the circuitry is homologous. Etymology Caridoid is derived from the Greek or (pronounced "kah-RISS"), shrimp or prawn, which is the root of the name of the taxonomic infraorder Caridea, a large group of crustaceans also known as the caridean shrimp. See also Crayfish Lateral giant interneuron Medial giant interneuron Command neuron Fixed action pattern Central pattern generator Coincidence detection in neurobiology Pain in crustaceans References Suggested reading Roberts, A., Krasne, F. B., Hagiwara, G., Wine, J. J., and Krarner, A. P. (1982) "Segmental giant: Evidence for a driver neuron interposed between command and motor neurons in the crayfish escape system". Journal of Neurophysiology. 47: 761–781. Wine, J.J. and Hagiwara, G. (1977) "Crayfish Escape Behavior I. The Structure of Efferent and Afferent Neurons Involved in Abdominal Extension". The Journal of Comparative Physiology-A 121: 145–172. External links The Lobster Conservatory includes information on the biology and conservation of lobsters. The majority can be applied to crayfish due to common ancestry and homology. Neural and tail anatomy provides an idea of the organization of the segmental ganglia in the tail of the crayfish. The second diagram on the page is a transverse section through the tail that highlights the positions of the LGI, MGI and non-giant neurons. At the bottom of the page it also has diagrams of the tail flips caused by stimulation of the LGI (on the left half of the diagram) and the MGI (on the right half of the diagram). This accurate diagram appears to be similar to that found in Wine and Krasne's 1972 publication. Lobster Body Plan presents information on decapod anatomy. Cornell University's Neuroethology Course page Neuroethology Marine biology