Meeting Abstract
P2.56 Friday, Jan. 4 Intramandibular bending and an “umbrella-like” jaw protrusion mechanism in the kissing gourami WALSH, K.M.*; GIBB, A.C.; ARENA, A.; PACE, C.; Harvey Mudd College, Claremont; Northern Arizona Univ., Flagstaff; Northern Arizona Univ., Flagstaff; Northern Arizona Univ., Flagstaff kwalsh@hmc.edu
Kissing gourami Helostoma temminkii have an unusual jaw morphology that enables them to perform the eponymous �kissing� behavior. We note two key aspects of these unusual jaws: kissing gourami (1) employ a novel and previously unrecognized mechanism of upper jaw protrusion and (2) use this jaw protrusion mechanism in combination with intramandibular (i.e., within the lower jaw) bending to scrape algae from the substrate. To quantify feeding kinematics and to ascertain the mechanism that generates these unusual movements, we filmed live kissing gourami feeding on encrusting algae and compared them to preserved specimens that we manipulated to mimic natural movements. We found that rotation of the angular bone of the lower jaw is key to generating both upper jaw protrusion and intramandibular bending. Upper jaw protrusion occurs via an �umbrella-like� mechanism, whereby the angular bone rotates and serves as the �runner� that pushes the maxilla (the �stretcher�) and the premaxilla (the �rib�) of the upper jaw into a protruded position. Intramandibular bending occurs when the dentary (the anterior lower jaw) forms an 80° angle relative to the angular (the posterior lower jaw). These movements allow a freely-feeding kissing gourami to generate a gape of over 180° (i.e., jaws flush with the substrate). We also noted a previously undescribed tendon from the jaw adductor (adductor mandibulae) to the dentary, which we posit assists in the retraction of the lower jaw. In addition, iron-tipped teeth are embedded in cartilaginous elements within the lip ligaments. We conclude that the unique jaws of the kissing gourami facilitate maximum contact between the teeth and the substrate; this may allow them to obtain encrusting algae that other fish cannot readily procure.
