WHAT IS A MOLLUSK? Why are animals that look and act so different grouped in the same phylum? It is because they share developmental patterns.
Characteristics of Mollusk 1. mantle 2. mantle cavity 3. shell 4. true coelom 5. head, muscular foot, visceral cavity 6. systems: circulatory, respiratory, digestive, excretory, reproductive, and nerve impulses
Mollusks are well defined as soft bodied animals that either have an external or internal shell. Their name comes from the Latin word molluscus meaning soft.
Most mollusks are composed of 4 basic parts: • foot - flat surface adapted for locomotion and usually contains the mouth and other feeding structures • mantle - covers most of the body and secretes the shell • shell - composed of calcium carbonate • visceral mass - contains the internal organ
Unique features of most mollusks include • Mantle • ctendia - special gill which are also used for filter feeding • radula - rasping tongue-like structure used for scraping
INTERNAL TRANSPORT OPEN CIRCULATORY SYSTEM In open circulatory systems, the blood is not always contained in vessels. There is a simple heart and a few arteries but there are no veins. Blood leaves the heart and bathes the internal organs and travels through the body in open spaces called sinuses. These sinuses lead the blood to the gills where oxygen and carbon dioxide are exchanged(diffusion).
Excretion - All animals must remove waste products An open circulatory system will work well for slow moving animals. Why is an open circulatory system not adequate for fast-moving animal