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The Gastrotrich (a small aquatic animal) lives only for three days.
pygmy goby (vertebrate(fish))(59 days)
flies 34 - 36 days
The gastrotrich (a minute aquatic animal) lives the shortest - three days.
[JRT: the question asks about a mammal, which the gastrotrich isn't.]
Gastrotrichs are microscopic marine animals that have worm shaped bodies. They eat decaying matter, bacteria, algae, as well as protists.
gastrotrich lives the shortest it lives three days