Mollusks are a diverse group but they all share similar traits.
Mollusks are found in almost every habitat and include creatures such as snails, octopus, clams, abolones, mussels and oysters. With over 100,000 different species, mollusks are a diverse group. Despite their diversity, mollusks all share at least three distinct characteristics. All mollusks have three distinct parts: the muscular foot, the head and the visceral mass. These creatures also have a body cavity known as a coelom. Most mollusks are marine animals but some also live in freshwater habitats and on land.
Body Cavity
All mollusks have a body cavity known as a true coelom, according to the author Christopher Smith in his book "Biology of Sensory Systems." The coelom is a collection space for the mollusk's waste fluids. The coelom helps the mollusk in a number of ways. The coelom suspends the internal organs in fluid, which cushions them and protects them from injury. This separation of the organs from body muscles allows food to move through the mullosk's digestive system without interfering with muscle movement.
Head
The head of the mollusk contains the mollusk's mouth, nervous system and sensory system. The head region of the mollusk has small, interconnecting "brains" known as ganglionic centers. These ganglionic centers connect nerves, motor organs and sensory organs. In higher forms of mollusks such as snails and octopus, the ganglionic centers are concentrated in the head region. In lower forms of mollusks, like chitons, the ganglionic centers start at the head and run through the length of the body.
Visceral Mass
The visceral mass contains the vital organs such as the digestive, reproductive, circulatory, and excretory systems. The digestive system contains an esophagus, stomach, liver, intestines and anus. Some mollusks have an open circulatory system where blood is pumped into sinuses containing tissue, while others have a closed circulatory system where blood is pumped into blood vessels, according to the author Eldra Pearl Solomon in her book "Biology." Some mollusks also have either male or female sex organs in their reproductive system while others have both male and female sex organs. The mollusk's excretory system is located in the anus and secretes waste fluids to the coleum.
Foot
Mullosks have a singular foot that allows the mullosk to move around. The foot is muscular and is formed from muscles within the body wall. The foot is also covered with numerous mucus glands. The exterior skeleton of the mollusk provides the foot with support. The foot moves the mollusk by flexing the muscles in the foot as well as by grasping and clinging to surfaces with mucus secreted from the glands in the foot.
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