Gross and Histopathological Signs of the Spotting Disease in the Sea Urchin <i>Strongylocentrotus intermedius</i>

Abstract

Histopathological and scanning electron microscopic observations were performed in the lesional tissues of the test and appendages of the sea urchin Strongylocentrotus intermedius affected by “spotting disease.” Spotting lesions with blackish red color on the test surface, separation of spines and attachment failure of tube feet are typical external signs. The epidermal lesions of the test and appendages is disorganized and infiltrated by migrating coelomic red spherule cells (eleocytes) and brown granules. Muscle fibers in the spine base, tube feet and ampullae are fragmented. These pathological signs are very similar to those of the bald-sea-urchin disease in S. purpuratus and S. droebachiensis. Invasions of the ameba Paramoeba invadens that was identified as a pathogen of thebald-sea-urchin disease, were not found in the diseased S. intermedius. However, seriously damaged epidermis, dermis and connective tissue were invaded by bacteria, one of which was a filiform bacillus. The results suggest that the spotting disease of S. intermedius would associate with a bacterial infection.