Cross references:  Amphioxus Muscles     Myoseptum   

Myomere (Wiki) 
    "Myomere are the blocks of skeletal muscle tissue found commonly in chordates. They are commonly zig-zag, "W" or "V"-shaped muscle fibers. The myomeres are separated from adjacent myomere by connective tissues and most easily seen in larval fishes or in the olm. Myomere counts are sometimes used for identifying specimens, since their number corresponds to the number of vertebrae in the adults."