Nitric oxide (NO) Nitric oxide (NO), colourless, toxic gas that is formed by the oxidation of nitrogen. Though it has few industrial applications, nitric oxide performs important chemical signaling functions in humans and other animals and has various applications in medicine.
or British mollusc /ËmÉËlÉsk/. plural mollusks. Learner's definition of MOLLUSK. [count] biology. : any one of a large group of animals (such as snails and clams) that have a soft body without a backbone and that usually live in a shell.
Not all mollusks have shells. Mollusks are a group of soft-bodied animals that includes snails, scallops, clams, and sea slugs. Most mollusks have shells: univalves, like snails, have one shell; bivalves, like clams, have two. Some mollusks, such as the squid and octopus, have lost their shells during their evolution. With 41% of the 736 documented extinctions of all animal species, the number of mollusks exceeds that of any other major taxonomic group 3. 2  Most documented endangered mollusk species are non marine (they live in freshwater or terrestrial environments) 5.