protractor muscles

From ZooTerms (Dictionary of Invertebrate Zoology)
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protractor muscles: 1. A contractile muscle that functions to extend an organ.

2. (NEMATA) Muscles attached to the stylet knobs or base and anteriorly to the body wall or head skeleton.

3. (Sipuncula) In adult Xenosiphon and some larval forms, an extra pair of muscles attached to the introvert near the brain and to the body wall of the trunk anteriorly.