Attachment of eggs by Concinnocotyla australensis (Monogenea: Polystomatidae) to the tooth plates of the Australian lungfish, Neoceratodus forsteri (Dipnoi)

Abstract

Eggs of the polystome monogenean, Concinnocotyla australensis, were found attached to the crushing surface and sides of the tooth plates of the Australian lungfish, Neoceratodus forsteri, from the Brisbane River and Enoggera Creek in south-east Queensland, Australia. Scanning electron microscopy reveals that the crushing surface of the tooth plates of infected hosts can bear an extensive, carpet-like cover comprising enormous numbers of eggs. The eggs are attached firmly by eggshell material at the distal tip of the abopercular appendage. Our studies suggest that the eggs are laid singly soon after manufacture, embryonate while attached to the tooth plates, and hatch in situ to release an unciliated oncomiracidium. Attachment of eggs to the host by C. australensis, a rare strategy among monogeneans, achieves some of the advantages, and avoids some of the disadvantages, of ovoviviparity and full egg-embryonation before laying. Emergence of unciliated oncomiracidia permits auto-infection. However, a transfer of larvae or adults from host to host might occur, possibly during spawning, when male and female lungfish intertwine. Attachment of eggs to the tooth plates may reflect the suitability of their hard, non-secretory surface.