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

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. Several published reports have referred to various and isolated aspects of the cephalothoracic extrinsic muscles and the intrinsic musculature of the isopod gut. In a comprehensive description of the digestive anatomy of Edriophthalme, Ide (1892) noted only briefly foregut musculature, as did Reh6rst (1914). However, Ide observed a pair of extrinsic muscles forming a crosslike pattern, which he called the "Cross of St. Andrew." Jackson (1926) contributed significantly to our knowledge of isopod anatomy by way of a detailed description and discussion of the head endoskeleton and appendage musculature of Ligia oceanica. Nicholls (1931) provided a detailed account of foregut structure and its musculature in L. oceanica, as well as the processes of feeding, digestion, and absorption. Radu (1948) described the intrinsic and extrinsic muscles of the oniscoid esophagus, cardiac stomach, and pyloric stomachs, but he did not discuss their functinal relationships. Manton (1963) effectively complemented Jackson's work, integrating much scattered information to offer comprehensive functional morphologic interpretations of crustacean jaw mechanisms. The functional morphology of the alimentary canal in two carnivorous intertidal isopods, Eurydice pulchra and E. affinis, was treated by Jones (1968) in a comparison of the structural and functional modifications related to the carnivorous mode that characterizes the genus with those of herbivorous and omnivorous isopods. Schmitz and Schultz (1969) reported that the esophageal lumen of Armadillidium vulgare is opened and closed both by intrinsic and extrinsic muscles and contended that the gastric mill is moved in a similar manner to form a closing apparatus. Subsequently, Schultz (1973b) described the foregut musculature of Lirceus garmani, referring briefly to similarities in L. fontinalis (see also Schultz, 1973a). The work of Hassall (1977) detailed the structure, as well as the functional morphology, of the mouthparts and foregut in Philoscia muscorum. The purpose of the present paper is to contribute further to our knowledge of