This proposed mechanism requires that the glandulo-muscular cores antagonize the divaricator musculature so that the hook supports bend rather than simply shorten.
We found the nodus to be a relatively small structure at the base of the hook supports to which the hook support base, the divaricator muscle fibers, and the proboscis retractor muscles are all closely attached.
We consider each hook support as a beam with a medial tensile element (the connective tissue basement membrane surrounding the medial glandular region), a core of variable length (the glandulo-muscular core with its radial myofilament bundles), and a lateral contractile element (the divaricator muscle fibers).
The radial and divaricator musculature of the hook supports are inactive.
The translation and rotation required to open the hooks may be accomplished by the co-activation of both the radial myofilament bundles and the divaricator muscle fibers.
In the first phase, the divaricator muscles relax while the radial myofilament bundles of the glandulo-muscular core remain activated.
This is because without the antagonistic support provided by the glandulo-muscular core, either the activation of the divaricator muscle fibers or the tension within the basement membrane of the medial glandular region will return the hook supports to their shorter resting length.
Simultaneous contraction of the lateral divaricator muscle fibers results in a lateral bending, and thus opening of the hooks.
As a muscle articulation, the hook support musculature probably generates the force necessary for hook movement; hook opening forces may be generated by the divaricator muscle fibers and radial myofilament bundles, and closure may be the result of the hook support bending as its glandulo-muscular core lengthens because of asymmetric forces on either side.