Mussel Periostracum from Deep-Sea Redox Communities as a Microbial Habitat: The Scalloping Periostracum Borer

A complex and highly unusual eukaryotic microorganism was discovered to be penetrating and removing the periostracum of deep-sea mussels from the Florida Escarpment brine seeps at a depth of 3266 m. These brine seeps support a chemolithoautotrophic redox community similar to those known from Pacific hydrotherma! vents. This microorganism of unknown taxonomic affinity is filamentous and coenocytic, with a simple plasma membrane and no cell wall. It forms prostrate, radiating systems of branched tunnels, 8–15 u.m in diameter. The surface of the tunnels is sculptured by helically organized, scale-like depressions, which are left as scars in the process of periostracum removal by the organism. Periostracum is removed in discrete pieces (scallops) at the ends of the tunnels. This organism has been found at three Atlantic deep-sea redox communities, but not in similar communities of the Pacific.