Table of Contents
What are the layers of a shell?
This pattern of growth results in three distinct shell layers: an outer proteinaceous periosteum (uncalcified), a prismatic layer (calcified) and an inner pearly layer of nacre (calcified). In comparison, turtle shells are part of the vertebrate animal’s so-called endoskeleton, or skeleton from within the body.
What are the three layers of the shell?
The shell is made of three layers: the nacreous layer, an inner iridescent layer of nacre (mother-of-pearl) composed of calcium carbonate that is continuously secreted by the mantle, the prismatic layer, a middle layer of chalky white crystals of calcium carbonate in a protein matrix and the periostracum, an outer …
What is the outer layer of a mollusk shell?
The periostracum, the outermost organic layer, is secreted by the inner surface of the outer mantle fold at the mantle margin.
What is the outer shell made up of?
Earth’s outermost, rigid, rocky layer is called the crust. It is composed of low-density, easily melted rocks; the continental crust is predominantly granitic rock (see granite), while composition of the oceanic crust corresponds mainly to that of basalt and gabbro.
What are the two portions of a mollusk shell called?
Bivalves by definition possess two shells or valves, a “right valve” and a “left valve”, that are joined by a ligament. The two valves usually articulate with one another using structures known as “teeth” which are situated along the hinge line.
What are the different layers of the bivalve shell?
2.1. The valves are composed mostly of calcium carbonate and have three layers; the inner or nacreous layer, the middle or prismatic layer that forms most of the shell, and the outer layer or periostacum, a brown leathery layer which is often missing through abrasion or weathering in older animals.
What is the inner layer of a shell made of?
The calcium carbonate layers in a shell are generally of two types: an outer, chalk-like prismatic layer and an inner pearly, lamellar or nacreous layer. The layers usually incorporate a substance called conchiolin, often in order to help bind the calcium carbonate crystals together.
Are mollusks bilateral or radial?
Mollusks are generally considered a phylum of bilaterally symmetrical animals, although there are also many asymmetrical species. Bilateral symmetry means that an organism can only be divided into two equal halves if it is cut from top to bottom along the middle of the anterior-posterior (front-back) axis.
What is another term for a mollusk shell?
Valve. Another term for a mollusk shell. Radula. A rasping, tongue-like organ that is found in all mollusks except bivalves.
What holds the two shells together?
A hinge ligament made of elastic protein joins the two halves of the shell together, and large adductor muscles between the two valves hold them closed. When the shell is closed, the top part of the hinge ligament is stretched and the lower part is compressed.