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The morphology of the mandible and stomach lateralia in some Lake Baikal amphipods has been investigated in regard to their food preference. Six species of endemic amphipods with different life styles (so-called "life forms") have been studied by means of light and scanning electron microscopy. The modifications of the mandible are attributed to the food resources used. The position of the incisor and lacinia mobilis, their width and length, the structure of the triturative area of the molar, the wearing of incisor and lacinia mobilis between two moults, and the relative length of the stomach depend on the type of food. None of the species studied revealed complete reduction of any part of the mandible. The most specialized species are the oophage Pachyschesis bazikalovae G. Karaman, 1976, the necrophage Ommatogammarus albinus (Dybowsky, 1874), and a species biting holes in sponges with a siliceous skeleton, Eulimnogammarus violaceus (Dybowsky, 1874). The morphology of the lateralia seems not to be connected with the food type, but is probably important from a phylogenetic point of view. RÉSUMÉ La morphologie de la mandibule et des pièces latérales de l'estomac de certains amphipodes du lac Baïkal a été étudiée en relation avec leurs préférences alimentaires. Six espèces d'amphipodes endémiques ayant des modes de vie différents (désignés par le terme "life forms") ont été examinées au microscope électronique à balayage et au microscope optique. On a montré que les modifications de la mandibule sont déterminées par le type d'aliments utilisés. La position du processus incisif et de la lacinia mobilis, la largeur et la longueur de ces pièces, la structure de la surface broyeuse du processus molaire, l'usure subie par le processus incisif et la lacinia mobilis pendant l'intermue, ainsi que la longueur relative de l'estomac dépendent du type de nourriture. Parmi les espèces examinées, aucune n'a subi la réduction totale d'une partie ou d'une autre de la mandibule. Les espèces les plus spécialisées sont l'oophage Pachyschesis bazikalovae G. Karaman, 1976, le nécrophage Ommatogammarus albinus (Dybowsky, 1874) et une espèce inquiline Eulimnogammarus violaceus (Dybowsky, 1874) qui vit dans des cavités qu'elle creuse dans des éponges à squelette siliceux. La 1 )

BackgroundIn crustaceans, several mechanisms provide for the mechanical strength of the cuticular “tools” (dactyli, claws, jaws), which serve to catch and crush food objects. Studies on the mandibles of the endemic Baikal amphipod Acanthogammarus grewingkii by means of electron microscopy and elemental analysis have revealed specific structural features of these mouthparts.MethodologyThe fine structure of the mandible has been studied by means of SEM, TEM, and AFM; methods used to analyze its elemental and phase composition include XEPMA, XPS, SEM-EDS analysis, and XRD.ConclusionFunctional adaptations of the mandible in A. grewingkii provide for the optimum combination of mechanical hardness and fracture resistance, which is achieved due to a complex structure and composition of its cutting parts. Teeth of the mandible are covered by a thin layer of silica (10–20 µm). Their epicuticle is characterized by a high density, consists of three layers, and increases in thickness toward the tooth apex. The epicuticle is enriched with Br, while the concentrations of Ca and P reach the peak values in the softer internal tissues of the teeth. These data broaden the view of the diversity of adaptation mechanisms providing for the strengthening of cuticular “tools” in crustaceans.