Dugong feeding behaviour
(A) Upon approaching the vegetation the oral disk is flared. This involves contraction of the snout along its entire length, pulling the orofacial ridge dorsally and laterally. Simultaneously, the pair of lateral furrows open and expand, resulting in the extension of the lateral flaps and a shape change of the oral disk from arched and convex to semicircular and flat.
(B) Perioral bristle movement (U1 and U2) begins near the midline, adjacent to the central crease. The upper lip (ventral margin of the oral disk) is lifted slightly to either side of the central crease of the oral disk to form a small, characteristic ‘M’ shape. The lip margin, where the U1 bristle fields are located, curls rostrally.
(C) Both U2 bristle fields are maximally everted rostrally near the midline, and each field begins to move laterally. Simultaneously, the raised peaks of the upper lip travel laterally in a wave-like action. At this time the lower jaw begins to open.
(D) At the ventrolateral corner of the oral disk the U2 bristle fields change directions and move caudally. During these events, the lower jaw continues to open and reaches its maximum gape. The L1 are everted to their full extent from the fleshy lower lip pad.
(E) The U2 bristles move medially to complete a circular motion that sweeps vegetation into the side of the mouth, and then return to their original position (rostral). As the lower jaw closes, the L1 bristle fields sweep vegetation caudally into the oral cavity.
Orofacial morphology and feeding behaviour of the dugong, Amazonian, West African and Antillean manatees (Mammalia: Sirenia): functional morphology of the muscular-vibrissal complex. Christopher D. Marshall, Hiroshi Maeda, Matsumitsu Iwata, Masami Furuta, Shiro Asano, Fernando Rosas and Roger L. Reep. Journal of Zoology / Volume259 / Issue03 / March 2003, pp 245-260 DOI: http://dx.doi.org/10.1017/S0952836902003205 (About DOI), Published online: 10 March 2003 (pdf)