New observations on the ciliate genus Vestibulongum (Pycnotrichidae): vestibular ultrastructure, macronuclear endosymbiotic bacteria, biogeography, and evidence for host specificity.

Two isolates of the pycnotrichid ciliate genus, Vestibulongum, were collected from the host fish, Acanthurus xanthopterus, from two locations in the Southern Pacific Ocean. One was from the Great Barrier Reef (GBR), and a second from Papua New Guinea. These sites are thousands of km from the type locality, off the coast of South Africa. New data were collected from protargol-stained samples to more fully characterize the general form and light microscopic structures of the ciliate. Specimens from all three sites had a long vestibule, characteristic of most members of the family. Data suggest that specimens from each site are the same genus. The kinetids of the Vestibulongum isolated from the GBR contained the typical components of postciliary, transverse, and nemodesmatal microtubules, and Kd fibrils. Also, two quite different forms of endomacronuclear bacteria were observed and are described. One of those has distinct endospores, which are similar to endospores in nuclear endosymbiotic bacteria in a species of Balantidium from the gut of another species of surgeonfish.