sarcosome

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A large specialized mitrochondrion found in striated muscle.

from The Century Dictionary.

• noun The fleshy part of a coral.
• noun The darker and actively contractile portion of a muscle fibril.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a large mitochondrion in a striated muscle fiber