Osmoconformers are marine organisms that maintain an internal environment which is isotonic to their external environment. This means that the

osmotic pressure Osmotic pressure is the minimum pressure which needs to be applied to a Solution (chemistry), solution to prevent the inward flow of its pure solvent across a semipermeable membrane. It is also defined as the measure of the tendency of a soluti ...

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 is isosmotic to their external environment, the types of

ions An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

in the two environments differ greatly in order to allow critical biological functions to occur. An advantage of osmoconformation is that such organisms don’t need to expend as much energy as osmoregulators in order to regulate ion gradients. However, to ensure that the correct types of ions are in the desired location, a small amount of energy is expended on ion transport. A disadvantage to osmoconformation is that the organisms are subject to changes in the osmolarity of their environment.

Examples

Invertebrates

Most osmoconformers are

marine invertebrates Marine invertebrates are invertebrate animals that live in marine habitats, and make up most of the macroscopic life in the oceans. It is a polyphyletic blanket term that contains all marine animals except the marine vertebrates, including the ...

such as

echinoderms An echinoderm () is any animal of the phylum Echinodermata (), which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as larv ...

(such as starfish),

mussels Mussel () is the common name used for members of several families of bivalve molluscs, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, whic ...

, marine crabs, lobsters,

jellyfish Jellyfish, also known as sea jellies or simply jellies, are the #Life cycle, medusa-phase of certain gelatinous members of the subphylum Medusozoa, which is a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animal ...

, ascidians ( sea squirts - primitive chordates), and scallops. Some

insects Insects (from Latin ') are hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of jointed ...

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.

Craniates

There are a couple of examples of osmoconformers that are craniates such as

hagfish Hagfish, of the Class (biology), class Myxini (also known as Hyperotreti) and Order (biology), order Myxiniformes , are eel-shaped Agnatha, jawless fish (occasionally called slime eels). Hagfish are the only known living Animal, animals that h ...

, skates and

sharks Sharks are a group of elasmobranch cartilaginous fish characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the ...

. Their body fluid is isosmotic with seawater, but their high osmolarity is maintained by making the concentration of organic solutes unnaturally high. Sharks concentrate urea in their bodies, and since urea denatures proteins at high concentrations, they also accumulate trimethylamine N-oxide (TMAO) to counter the effect. Sharks adjust their internal osmolarity according to the osmolarity of the sea water surrounding them. Rather than ingesting sea water in order to change their internal salinity, sharks are able to absorb sea water directly. This is due to the high concentration of urea kept inside their bodies. This high concentration of urea creates a

diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...

gradient which permits the shark to absorb water in order to equalize the concentration difference. The

crab-eating frog The crab-eating frog (''Fejervarya cancrivora'') is a frog native to south-eastern Asia including Taiwan, China, Sumatra in Indonesia, the Philippines and more rarely as far west as Orissa in India. It has also been introduced to Guam, most lik ...

, or Rana cancrivora, is an example of a vertebrate osmoconformer. The crab-eating frog also regulates its rates of urea retention and excretion, which allows them to survive and maintain their status as osmoconformers in a wide range of external salinities. Hagfish maintain an internal ion composition plasma that differs from that of seawater. The internal ionic environment of hagfish contains a lower concentration of

divalent In chemistry, the valence (US spelling) or valency (British spelling) of an atom is a measure of its combining capacity with other atoms when it forms chemical compounds or molecules. Valence is generally understood to be the number of chemica ...

ions (Ca2+, Mg2+, SO4 2-) and a slightly higher concentration of monovalent ions. Hagfish therefore have to expend some energy for osmoregulation.

Biochemistry

Ion gradients are crucial to many major biological functions on a cellular level. Consequently, the ionic composition of an organism's internal environment is highly regulated with respect to its external environment. Osmoconformers have adapted so that they utilize the ionic composition of their external environment, which is typically seawater, in order to support important biological functions. For instance, seawater has a high concentration of

sodium ion Sodium is a chemical element; it has symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable isotope ...

s, which helps support

muscle contraction Muscle contraction is the activation of Tension (physics), tension-generating sites within muscle cells. In physiology, muscle contraction does not necessarily mean muscle shortening because muscle tension can be produced without changes in musc ...

and neuronal signaling when paired with high internal concentrations of

potassium ion Potassium is a chemical element; it has symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to form flaky white pot ...

References

{{Animalosmo Marine biology Homeostasis