In a tide pool, a student encounters an organism with a hard outer covering that contains much calcium carbonate, an open circul
atory system, and gills. The organism could potentially be a crab, a shrimp, a barnacle, or a bivalve. The presence of which of the following structures would allow for the most certain identification of the organism? a. a heart
b. a filter-feeding apparatus
c. a mantle
d. a body cavity
e. eyes
