S1-1.1 Jan. 4 The structure and function of the hooks of a turbellarian flatworm: A vermetically sealed muscle articulation UYENO, T.A.*; KIER, W.M.; University of North Carolina at Chapel Hill firstname.lastname@example.org
This study investigates the functional morphology of the grasping hooks of the proboscis of an interstitial turbellarian flatworm (Suborder Kalyptorhynchia). The hooks, which are used in predation, do not articulate with one another and instead are embedded in muscle and connective tissue. Thus, they resemble the “muscle articulations” of the beaks of octopus and the jaws of polychaetes where solid muscle blocks composed of multiple fiber orientations allow the joint flexibility, move the beaks or jaws, and bear bite reaction forces. Confocal and conventional light microscopy was used to investigate the arrangement of the muscle and connective tissue fibers. In contrast to previously described muscle articulations, the muscles that support and move the hooks appear to include parallel muscle fiber arrays of a single orientation. Also observed were several connective tissue bands that may control and limit deformations along one axis. The hooks may be rotated open by the co-activation of transversely arranged muscle fibers that push the hook base forward and longitudinal muscle fibers that draw the hook tips back. The hooks may be closed by activation of a transverse muscle fiber layer in conjunction with medially/longitudinally arranged connective tissue bands. Muscle articulations may therefore be more widespread and diverse in structure and function than previously recognized.