Extracellular matrix in some microturbellarians

Electron microscopy was used to study the ECM (extracellular matrix) in the epidermis, brain, and parenchyma of the catenulid turbellarians Stenostomum leucops leucops and Stenostomum leucops aquariorum and of the proseriates Archiloa unipunctata and Promonotus schultzei . Specimens were fixed with a tannic-acid fixation that enhances staining of extracellular proteins (TARI method) or a conventional electron microscopical method. Differences between species were found in the amount of matrix and extracellular fibrils. The morphology of ECM in these and other flatworms indicate that it could be an internal medium for transport and exchange of substances among cells. Variability in the structure of ECM among species probably does not reflect evolutionary relationships.