Integument of Maxmuelleria lankesteri (Echiura), with notes on bacterial symbionts and possible evidence of viral activity

The integumental ultrastructure of the trunk and proboscis of the echiuran Maxmuelleria lankesreri is described. In the trunk, a complex cuticle overlies an epithelium of support and secretory cells. The proboscis has a typical ciliated epithelium with a simpler cuticle but more microvilli than the trunk. A close similarity with the integument of Urechis caupo suggests a high degree of morphological conservatism in echiurans. Rod-shaped bacteria were found in the basal cuticle of the trunk. The most striking and unexpected feature of the hunk integument was the presence, in the cytoplasm and nuclei of support cells, of crystalline arrays that may be viral in origin.