Ultrastructure of the flame bulbs of the Monopisthocotylean MonogeneaLoimosina wilsoni(Loimoidae) andCalceostoma herculanea(Calceostomatidae)

Abstract

The flame bulbs of Loimosina and Calceostoma consist of a row of external and a row of internal longitudinal ribs connected by a « membrane » apparently of extracellular matrix, and two cytoplasmic cords connected by a septate junction. Internal ribs are continuous with the terminal cell, external ribs and cytoplasmic cords with the proximal canal cell. Both species have many internal leptotriches, in the first, some external leptotriches were also seen. Internal leptotriches arise from the perikaryon of the terminal cell or the internal ribs. The flame bulbs closely resemble those of the Monogenea Polyopisthocotylea examined and of Gyrodactylus, Dactylogyrus and an unidentified ancyrocephaline, i. e. evidence available indicates that all Monogenea share one type of flame bulb, also found in aspidogastreans and digeneans, but different from that of gyrocotylids, amphilinids and cestoideans. Udonella has a different type of flame bulb and, therefore, is unlikely to be a monogenean.