Using light and electron microscopy, we focused on the origin and organization of the trophosome in order to determine whether it resembles the complex vestimentiferan trophosome derived from the visceral mesoderm (as suggested by the relationship between Sclerolinum and Vestimentifera), the somatic mesodermal Osedax trophosome, or the endodermal organized frenulate trophosome.
The trophosome of Sclerolinum contortum is clearly derived from the visceral mesoderm. Most of the trophosome is an apolar tissue strand composed of bacteriocytes and mesenchyme anteriorly and of bacteriocytes surrounded by a peripheral peritoneum posteriorly.