Ideally animals store water in their blood or metabolize their fat reserves. I am aware of these methods but that’s not the approach I’m going for. Instead I though of an animal that secretes a slime sack which serves to store water in large quantities. The animal is closely related to amphibians like frogs and salamanders. It uses this adaptation travel on dry land in order to reach distant lakes or ponds, which would be otherwise distant for ordinary amphibians due to drying out.
You're probably thinking “why not store water normally?”
Cane toads have dry and warty skin that makes them less susceptible to the environment. This slime-sack adaptation however allows the animal to absorb ambient water like dew or rain during its journeys. In addition it allows the animal to store more water compared to its body size, though of course a larger sack is harder to carry. Due to gravity the sack will hang under the stomach, shielded from the sun. Thin mucus on the skin also absorbs water and transfers it to the sack via gravity.
The mucus is similar to hagfish slime which has the desired properties.
Hagfish slime is a protein-based, jelly-like substance emitted by hagfish as protection against predators. The slime is made up of strands that are stronger than nylon, thinner than human hair, and very flexible. Because of these unusual properties, hagfish slime is used to produce durable, environmentally-friendly fabric.
Unlike other types of mucus, however, hagfish slime doesn’t dry out.
The mucin is made up of long, thread-like fibers, similar to spider silk. These strands, which are arranged in bundles called skeins, are thinner than human hair, stronger than nylon, and extremely flexible. When the skeins come into contact with seawater, the glue holding them together dissolves, allowing the slime to expand rapidly. It is said that one hagfish can fill a five-gallon bucket with slime in only a few minutes.
Would this adaptation work? If not, why? What additional adaptations would the animal need to make use of this?