Because their internal osmolarity is similar to that of seawater, osmoconformers tend not to lose or gain water by osmosis. Thus, the correct option is A.
An osmoconformer is an animal that is iso-osmotic with its external environment. All osmoconformers are marine animals. And, because an osmoconformer's internal osmolarity is the same as that of its external environment, there is no tendency to gain or lose water.
Most of the marine invertebrates including starfish, crabs, jellyfish, lobsters, sea squirts, and scallops are osmoconformers. Such organisms do not need to expend as much energy as osmoregulators in order to regulate ion gradients in the water.
Therefore, the correct option is A.
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