Mollusks essays

Mollusks essays Everything You Ever Wanted to Know about Mollusks Mollusks: soft, squishy, slimy, and in some cases tasty animals. Mollusks have a soft body that may be protected by a hard shell. Some mollusks have hard outer shells, such as snails, while others have a light internal shell (squids) or no shell at all (octopuses). There are three characteristics that all mollusks have in common. First of all, mollusks have a mantle. This is their soft outer tissue layer. The mantle, in some species is what produces the hard outer shell. Secondly, mollusks have a muscular foot, which they use to move or hang on. The muscular foot appears in different ways on different mollusks. Third, between the mantle and the foot, there is the visceral mass. Most of the internal organs are located here. There is one more characteristic that most, but not all mollusks share. This is an open circulatory system in which blood flows freely over body tissues and organs. Although not all mollusks have separate sexes, they all reproduce sexually. Reproduction can involve internal or external fertilization. Internal fertilization occurs when a male mollusk transfers sperm into the female mollusk. After the eggs are fertilized, the female deposits them in a safe place for them to grow. External fertilization occurs when two mollusks release sperm and eggs into the water at the same time. The four most well known classes of mollusks are Cephalopoda, Gastropoda, Polyplacophora, and Bivalvia. Class cephalopod includes nautilus, squids, cuttlefish, and octopuses. Modern cephalopods are very much the same as their ancestors. They have very developed nervous systems and a closed circulatory system. Gastropods include mollusks such as snails, slugs, and conches. To feed, gastropods scrape algae, shred leaves, or capture prey with their radula. Some gastropods have destroyed millions of dollars in crops. Polyplacophoras most closely resemble ancient mollusks. Their shell i...