Table of Contents
What is the function of the mollusk shell?
In nature, mollusk shells have a role in protecting the soft body of the mollusk from predators and from the external environment, and the shells consist mainly of calcium carbonate and small amounts of organic matrices. Organic matrices in mollusk shells are thought to play key roles in shell formation.
What are the external features of molluscs?
The most obvious external molluscan features are the dorsal epidermis called the mantle (or pallium), the foot, the head (except in bivalves), and the mantle cavity.
What are the external shells of mollusks made of?
Seashells are the exoskeletons of mollusks such as snails, clams, oysters and many others. Such shells have three distinct layers and are composed mostly of calcium carbonate with only a small quantity of protein–no more than 2 percent. These shells, unlike typical animal structures, are not made up of cells.
What is the composition of a mollusk shell?
Shells are almost always composed of polymorphs of calcium carbonate – either calcite or aragonite. In many cases, such as the shells of many of the marine gastropods, different layers of the shell are composed of calcite and aragonite.
What are the main morphological features of molluscs?
Characteristic Features of Phylum Mollusca
- They are bilaterally symmetrical.
- They are triploblastic, which three layers.
- They show organ system grade of organisation.
- The body is soft and unsegmented.
- Body is divisible into three regions – head, a visceral mass, and ventral foot.
- Body is covered by a mantle and shell.
Why do all mollusks have shells?
As the mollusk ages, the shell becomes thicker and sturdier. As such, older mollusks usually have strong shells. The primary purpose of the shell is protection. It protects the animal against predators and guards the internal organs.
How does the mollusk build and repair its shell?
The mantle deposits calcium into a protein matrix to make the shell. The inner crystalline structure prevents cracks from breaking the shell, and the mantle continually repairs the shell from the inside.
What kind of tissue does a mollusk have?
Mollusks are invertebrates such as snails, scallops, and squids. Mollusks have a hard outer shell. There is a layer of tissue called the mantle between the shell and the body. Most mollusks have tentacles for feeding and sensing, and many have a muscular foot. Mollusks also have a coelom]
What does the head of a mollusk do?
Most mollusks have a distinct head region. The head may have tentacles for sensing the environment and grasping food. There is generally a muscular foot, which may be used for walking. However, the foot has evolved modifications in many species to be used for other purposes.
How are proteins secreted into the mollusc shell?
They are secreted into the extrapallial space by the mantle, which also secretes the glycoproteins, proteoglycans, polysaccharides and chitin that make up the organic shell matrix. Insoluble proteins tend to be thought of as playing a more important/major role in crystallization control.
Where does growth take place in a mollusc shell?
The shell is deposited within a small compartment, the extrapallial space, which is sealed from the environment by the periostracum, a leathery outer layer around the rim of the shell, where growth occurs. This caps off the extrapallial space, which is bounded on its other surfaces by the existing shell and the mantle.