Osmoconformer

Osmoconformers are marine organisms that maintain an internal environment that is isosmotic to their external environment. This means that the osmotic pressure, or osmolarity, of the organism’s cells is equal to the osmotic pressure of their surrounding environment. By minimizing the osmotic gradient, this subsequently minimizes the net influx and efflux of water into and out of cells. Even though osmoconformers have an internal environment that's isosmotic to their external environment the types of ions in the two environments differ greatly in order to allow critical biological functions to occur. A benefit to osmoconformation is that organisms don’t need to expend as much energy as osmoregulators in order to regulate ion gradients. However, to ensure the correct types of ions are in their desired location, a small amount of energy is expended on ion transport. A disadvantage to osmoconformation is that organisms are subject to changes in the osmolarity of their environment.

Most osmoconformers are marine invertebrates such as echinoderms (such as starfish), mussels, marine crabs, lobsters, jellyfish, ascidians (sea squirts - primitive chordates), and scallops. Some insects are also osmoconformers. Some osmoconformers, such as echinoderms, are stenohaline, which means they can only survive in a limited range of external osmolarities. The survival of such organisms is thus contingent on their external osmotic environment remaining relatively constant. On the other hand, some osmoconformers are classified as euryhaline, which means they can survive in a broad range of external osmolarities. Mussels are a prime example of a euryhaline osmoconformer. Mussels have adapted to survive in a broad range of external salinities due to their ability to close their shells which allows them to seclude themselves from unfavorable external environments.

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