CEPHALOTHORACIC MUSCLES OF THE FOREGUT AND FEEDING APPENDAGES OF ARMADILLIDIUM VULGARE (LATREILLE) (CRUSTACEA: ISOPODA)

ABSTRACT The cephalothoracic muscles associated with the foregut and feeding appendages of Armadillidium vulgare (Latreille) are described with a view toward establishment of functional morphologic relationships based on studies of dissections, special endoskeletal preparations, and whole-organism serial sections. The complex endoskeleton of the head resembles that of Ligia oceanica in certain aspects. The maxillipeds flex only weakly, but are capable of strong adduction and anterior-posterior movement. The maxillae are weak appendages, but the complex musculature of the maxillules suggests powerful movements associated with food manipulation. The asymmetric mandibles are triturating appendages moved by adductors and abductors. The labrum is held in place over the mouthparts by muscles that permit only slight mesial movements when the mandibles are opened. Musculature of the esophagus includes circular and longitudinal intrinsic bands and 17 pairs of extrinsic dilators. Coordinated sequential dilation and constriction along the length of the esophageal tube produces peristaltic-like movements. The triturating function of the gastric mill is effected by five pairs of extrinsic muscles. Intrinsic circular muscle constricts the pressing apparatus; two pairs of extrinsic muscles contract simultaneously to dilate the press. The foregut appears to be modified for food handling, transport, storage, trituration, pressing, and straining of food.