Types of Circulatory Systems Open Circulatory System Closed Circulatory System

Open Circulatory System Common to mollusks (clams), crustaceans (shrimp), insects, and other invertebrates. Blood circulates by diffusing back to the heart system between cells. All cells need to be within 1 cell from blood so the blood can soak through the body.

Example of Open Circulatory System

Closed Circulatory System Almost all Vertebrates (animals with a backbone) have a closed circulatory system. Closed circulatory systems have blood closed within vessels of different sizes. Blood is pumped by a heart through vessels and does not fill body cavities.

Example of Closed Circulatory System

The Clam The clam is an animal that burrows under the sea floor. Clams have open circulatory systems. They are bivalves, which are mollusks that have two shells that protect a soft body. There are over 15,000 different species of clams worldwide. The clams you will receive are Quahog clams or Chowder Clams (whatever the fish-monger has).

Valves Clams have 2 valves. In clam anatomy: valves open and close to protect the clam and allow water to flow into and out of the animal. The valves are essentially shells.

Three Body Regions The clam is made up of three body regions: Head-foot Mantle Body

Mantle The mantle coats the inside of the shells. It is a thin film that regenerates the shells as the clam grows. In short: the mantle grows the shells.

Body The body is a soft cavity that contains the digestive, circulatory, reproductive, and nervous systems. When people eat clams, they eat the body.

Head-Foot The head-foot is attached to the body It is used to help the clam move. It also helps the clam burrow (dig a hole) to bury itself in the sand for protection.

Siphons There are 2 siphons –Excurrent siphon and incurrent siphon They are 2 tube like structures that suck in water and food (incurrent) and flush out water and waste (excurrent).

Umbo The hinge area at the top of the clam. It holds the shells (valves) together.

Heart The clam runs on an open circulatory system. The heart is found in the darkened area hidden underneath the umbo.

Gills Clams do not have lungs The have gills (like fish) for breathing. The gills are striated (striped).

Anterior and Posterior Retractor Muscles The clam has 2 muscles that allow the clam to open and close. Anterior means left side. Posterior means right side.