divaricator
From ZooTerms (Dictionary of Invertebrate Zoology)
divaricator (noun; Latin divaricatus, spread apart): 1. A muscle which causes parts to open.
2. (Brachiopoda) A muscle from the ventral valve to the cardinal process which opens the shell.
3. (Bryozoa) One of a pair of muscles which open the mandible for an avicularium or an operculum.
