Parasites and Symbionts (?) in Mussels (Bathymodiolus sp.)
from Cold Petroleum Seeps in the Gulf of Mexico

1a, b, c. Gill "rosettes" of unknown affinity are associated with the bacteriocytes in the gill. They appear to originate at the basement membrane of the gill filaments, migrate to the surface, and frequently move through the gill surface, coming to lie outside the tissue between the gill filaments.

2a, b. Chlamydial/Rickettsia-like inclusions are found in the digestive diverticula and tubules. Some appear smooth, while others appear as a group of tightly-compacted short rods in multidirectional groups. 3a, b. Extracellular gill ciliates.

4. Bucephalus-like trematodes are found invading the gonad, often replacing all reproductive tissues. In heavier infections, gill, mantle, and digestive gland are invaded as well. Prevalence was 100% at one site. 5a, b. Gill "inclusions" often appear similar to to Chlamydia/Rickettsia inclusions, and also have a visible internal structure. These appear as long strands, either tightly or loosely compacted, and often in a whirled configuration. These are most often located near the distal end of the gill filaments.