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CAMBRIAN PERIOD

542-488 million years ago

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myotomes in chordate

MUSCULAR SYSTEM

The skeletal muscle of ancestral cephalochordates was organized to form V-shaped myotomes similar to those observed in fish. Homologs of the trapezius muscle also existed.

Myotomes first evolved in cephalochordates and are evident in the following photos of modern lancelets (Cameron, 2000). Additional muscles in Amphioxus surround the oral and pharyngeal areas and form an anal sphincter. A pair of trapezius muscles on the dorsal surface helps to expel water from the body. (Ruppert, from Harrison, 1997, p. 397-9).
myotomes in lancelet myotomes in lancelet