Heart
Located in the pericardial cavity (separate
from the coelomic cavity), in the throat region,
caudal and ventral to the gills. The heart is
two-chambered (atrium, ventricle), but contains
a thin walled sinus venosus leading into the
atrium, and a thick, elastic bulbus arteriosus,
leading out of the ventricle. It is typically not
very infbrmative on squash preps but important
for histopathology. The heart is also part of the
RES.