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Marine world is an ideal model for studying species diversity. The main reasons for this is the abundant availability of water, presences of a large area favorable for photosynthesis, and lesser temperature variations compared to land climatic conditions [1, 2]. The wide species diversity can be broadly attributed to variable primary productivity in different ocean zones according to light availability [3]. Members of different species therefore evolved differently based on the biological functions that are suitable for its own habitat; this led to a rise in different biomolecules sharing a common structure existing across species [4] but differing in the basic properties according to the requirements. Although this holds true for many biomolecules present today, nothing displays the extent of variation occurring in polysaccharides. Their essential nature coupled with more than 2.5 billion years of evolutionary history simultaneously resulted in organisms employing this molecule for many key functions. Although not different from other polymers (proteins, lipids), polysaccharides are the most studied, utilized and information dense on earth, with a common basic structure but with a multitude of derivatizations [5, 6].

Polysaccharides are high-molecular polymers, also called glycans, made up of repeated units of monosaccharides and bound to unique glycoside bonds. They are omnipresent in the biological world, with roles as diverse as energy storage, building the cellular framework, to encoding genetic information through generations [6]. They can be water soluble or insoluble, and their structural diversity stems from different derivatization reactions taking place. On the basis of monomeric units, they can be divided in to 2 categories: homopolysaccharide (composed of same monomers), and heteropolysaccharide (composed of 2 or more different monomers). However, due to the diversity of the polysaccharide family, a more general classification is based on the intended functions:

 Storage polysaccharides (glycogen, starch)

 Structural polysaccharides (chitin, cellulose)

 Hereditary (DNA, RNA); conjugated with nitrogenous bases.

Structurally, polysaccharides can be linear (cellulose, agar) or branched (amylopectins, arabinans) [7]. Marine polysaccharides are essentially derived from marine organisms, like algae, seaweeds, bacteria, corals, sponges, fungi, and crustaceans (organisms like shrimps, crabs, prawns, and lobsters). This chapter addresses the properties and major applications of polysaccharides from marine sources in biomedical, food, pharmaceutical and agrarian industries.