Browsing by Author "VIAL, CI"

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    CEPHALIC ANATOMY OF THE HERBIVOROUS FISH GIRELLA-LAEVIFRONS (OSTEICHTHYES, KYPHOSIDAE) - MECHANICAL CONSIDERATIONS OF ITS TROPHIC FUNCTION
    (1990) VIAL, CI; OJEDA, FP
    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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    COMPARATIVE-ANALYSIS OF THE HEAD MORPHOLOGY OF PACIFIC TEMPERATE KYPHOSID FISHES - A MORPHOFUNCTIONAL APPROACH TO PREY-CAPTURE MECHANISMS
    (1992) VIAL, CI; OJEDA, FP
    Vial & Ojeda (1990) proposed that the low diversity of herbivorous fishes observed among Percoids might be owing to the existence of morpho-functional restrictions of the feeding apparatus that hinder the acquisition of efficient mechanisms for cropping and ingesting plant material. The morphological and functional evidence presented therein for the herbivorous kyphoid Girella laevifrons indicates that its morphological specializations are related to structural decouplings of the anterior and posterior regions of the buccal cavity involving the jaw and the hyoid arch. Functionally, these decouplings allow the ingestion of algae in a continuous fashion at low energetic cost. In this study, we evaluate the general validity of the proposed model by means of a morphological and functional comparative analysis of the cephalic structures of the four most abundant Kyphosid species of the Chilean coast: the girellids Girella laevifrons (Tschudi), Girella albostriata Steindachner, and Graus nigra Philippi, and the scorpid Scorpis chilensis Guichenot. We found great osteological and myological similarities between the two strict herbivores, G. albostriata and G. laevifrons, thus suggesting that the mechanism previously described for the latter species corresponds very closely to that of the former. This mechanism provides for mandibular manipulation carried out independently by the upper jaw and for a decoupling of the lower jaw into two mechanical units. Graus and Scorpis display a somewhat different morphological design. Although both maintain the intrahyoid decoupling shared by all kyphosid species, they do not present mechanical independence between the upper and lower jaw, nor a capacity for intramandibular movements. In Graus, teeth are well developed, conical, and slightly curved toward the interior. These characteristics make possible a trophic mechanism primarily based on a strong biting especially well suited for carnivory. The structural plan of Scorpis appears more distant from species in the other two genera, althoug it shares with them characters such as the double tendon of the A1 muscle in the maxilla, the intrahyoid articulation, the type of teeth, their replacement system, and the general design of the suspensorium. The particular morphology of the adductor muscles, and the mandibular design of Scorpis suggest a trophic mechanism mainly based on a rapid suction. From a functional viewpoint, the structural differences encountered in the four species analyzed may be understood as modifications related to their different mechanisms of prey capture.