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Inner anatomy of a snail shown left. As shown, there are many different organs present.
All Molluscs have three main differentiating parts: the visceral mass, the mantle, and the foot. The visceral mass contains many of the organ systems, such as the respiratory and digestive systems. The mantle covers the entire body. The foot is used to allow the mollusc to move.
To the left are some of the different body plans that molluscs have. Notice that although they look different, they all have most of the same key parts.
Reproduction: Sometimes the sexes are separate and males and females develop early on. Some of them, such as Crepidula, have males turn into females when they mature. Some of them are hermaphrodites who have both male and female gonads. Most of them reproduce using sexual reproduction, but not always. Parthenogenesis (in which the offspring are essentially clones of the parent) is rare but not impossible. Much of the reproduction is done internally.
A diagram of the circulatory system of a bivalve is shown left.
The circulatory system of Molluscs is called an open circulatory system. This means it has a heart which pumps blood into the body cavities, so the tissues are covered in blood. Through the cells, the blood diffuses back into the circulatory system. Neat!
An organ called the nephridium is used to expel the waste products out of the body. These are also known as kidneys. Extant, or living, gastropods usually only have one.
Molluscs breathe using comb like gills called ctenidia. Respiration occurs in a cavity. When the mollusc inhales, it widens the cavity by lowering the bottom of it, causing low pressure. This allows the mollusc to intake oxygen. To exhale, the floor is brought up which increases the pressure in the cavity, causing the mollusc to expel.
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