CEPHALIC ANATOMY OF THE HERBIVOROUS FISH GIRELLA-LAEVIFRONS (OSTEICHTHYES, KYPHOSIDAE) - MECHANICAL CONSIDERATIONS OF ITS TROPHIC FUNCTION
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Date
1990
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Abstract
Structural and functional restrictions hindering the development of efficient mechanism for cropping and ingestion of algal material could constitute an explanatory hypothesis for the observed low diversity of herbivorous fishes. In this study, the cephalic structures of the herbivorous kyphosid fish Girella laevifrons (Tschudi 1844) are described, including a functional analysis of its alimentary apparatus. This species can be characterized by having: (i) a great freedom of movement between the dentary and articular-angular, (ii) a double insertion of the muscle adductor mandibulae Al in both faces of the maxilla, (iii) specialized teeth, long and flexible with a peculiar articular condyle at their anterior base, (iv) a mobile articulation between ceratohyal and dorsal hypohyal, and (v) a well developed branchiostegal system. A mechanism based on a mandibular manipulation associated with a slow suction of a large volume of water is proposed. This mechanism would allow the ingestion of large amounts of algae (as long stripes) in a continuous fashion. The combined activity of both an oral manipulation and buccal suction systems are possible by the existence of a decoupling of the anterior and posterior regions of the buccal cavity involving the jaw and the hyoid arch. The adaptive value of this mechanism is discussed in relation of the feeding strategies utilized by this species.
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GIRELLA, HERBIVORY, HEAD MORPHOLOGY, FEEDING APPARATUS, FUNCTIONAL DESIGN