The morphology, morphogenesis, culture and pathogenesis of a marine facultative parasitic ciliate, Mesanophrys sp., of the Dungeness crab, Cancer magister, and its occurrence in wild crustacean populations

A histophagous ciliate was found associated with Dungeness crab (Cancer magister) mortalities in the spring of 1990. Its morphology and stomatogenesis indicated that the ciliated protist was an undescribed species of the genus Mesanophrys. The organism possessed a unique interruption of argentophilic fibers between adjacent kinetosomes of OPK1 indicating that it was composed of two different but functionally related components, and a transient fourth ciliary field during stomatogenesis.;At the ultrastructural level, the ciliate possessed features in common with other scuticociliates. Cortical mitochondria were bipolar and closely apposed to the inner alveolar membrane. Kineties were mostly composed of typical scuticociliate dikinetids. Small parasomal sacs were observed in cultured but not parasitic ciliates. The ciliate was transformed in culture to a form that possessed putative muco-trichocysts in the anterior half of the cell.;Studies on in vitro culture revealed that the nutrient requirements of Mesanophrys sp. were not easily met; phospholipids were required for growth. Optimal growth rate was attained in a chemically defined medium that was adjusted to pH 7.2, specific gravity 1.020 and incubated at 20;A non-specific removal of circulating hemocytes occurred early in the disease. Host response in the form of nodule and granuloma formation to ciliate tissue damage was confined to the period in which circulating hemocytes were present. Proliferating ciliates were generally restricted to the connective tissue and vascular spaces of infected crabs. Reserve inclusion cell abundance was diminished as the disease progressed indicating that the pathogen was competing for host nutrients.;During late spring of 1990, examination of a small number of randomly collected Dungeness crabs revealed the presence of Mesanophrys sp. in the blood of moribund, dead and apparently healthy crabs that had recently molted. Collections made in late spring to summer of 1990-1992 indicated that the ciliate was more prevalent in males than females and at one of the two collections sites. Infections were also more prevalent in newly molted crabs than in pre-molt and new hard shell crabs.