Question

circulation
molluscs represent the second phylum we have studied whose members have a true circulatory system (brachiopods also possess a simple, open circulatory system). bivalves such as clams, mussels, and oysters have an open circulatory system—a system in which the blood is not always confined within a network of vessels. in bivalves, blood from tissues and major organs flows to the gills, where it is oxygenated and is directed passively back to the heart (fig. 11.9). the oxygenated blood enters through openings in the heart called ostia and is pumped out of the heart through arteries to the mantle, foot, and visceral mass, where it empties into open sinuses in the tissues of these regions. small veins collect the blood and return it to the gills.
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2.1 list several features of the freshwater clam that enable it to thrive as a sedentary, aquatic organism.
2.2 what is the excretory organ of bivalves? where in the body is it located?
2.3 why do you suppose the adductor muscles are so well - developed in bivalves?
2.4 describe how the gills of a clam are an example of a multifunctional organ.

Explanation:

2.1: Freshwater clams have a hard shell for protection, siphons for filtering food and water, and a muscular foot for attachment to surfaces.
2.2: The excretory organ of bivalves is the kidney (also called nephridium). It is located near the heart in the body.
2.3: Adductor muscles are well - developed in bivalves to close their shells tightly, protecting them from predators and desiccation.
2.4: Clam gills are multifunctional as they are used for respiration (gas exchange), feeding (filtering food particles from water), and sometimes for reproduction (releasing gametes into the water).

Answer:

2.1: Hard shell for protection, siphons for filtering, muscular foot for attachment.
2.2: Kidney (nephridium), near the heart.
2.3: To close shells tightly for protection.
2.4: Used for respiration, feeding, and sometimes reproduction.