Tapeworms lack coelom, conventional circulatory system and an inner intestine. They absorb nutrients through the syncytial surface epithelium. The extracellular matrix (ECM) thus plays a very important role for the distribution of all kinds of substances-including both nutrients and neuronal signal substances.
The ECM of the obligatory endoparasite, the gull-tapeworm Diphyllobothrium dendriticum, has been investigated by conventional electron microscopical methods, after lanthanum or ruthenium red impregnation, and by incubation in tannic acid (the TARI/TAGO method) according to Buma and Roubos (1986, Neuroscience, 17: 867 979). The ECM forms a thin networkbetween the cells in the cortical tissues. In the medullary tissue it also forms lacunae. The ECM is composed of non-striated fibres 12 14 nm in diameter and glucose amine glucanes (GAGs). In the lamina beneath the syncytial epithelium and surrounding the main and the peripheral excretory ducts the fibres are abundant. Around the parenchyma cells the fibres form a loose network.
Light microscopical immunocytochemistry has revealed fibronectin-, laminin-and collagen IV-like substances in the ECM of the worm. Human antibodies were used which indicates that these ECM substances are well conserved.