Protonephridial Excretory System in Vestimentifera (Siboglinidae, Annelida).

Ultrastructural study of the excretory tree of vestimentifera Ridgeia piscesae has shown that it consists of tubules that are blind at their distal ends. The tubules are lined with ciliated cells and have one or two multiciliated terminal cell(s) at the distal ends. In the tubule walls, there are putative ultrafiltration sites. The excretory tree tubules are interpreted as the secondary protonephridia.