Octopus
Reproduction is a cause of death: males can only live for a few months after mating, and females die shortly after their eggs hatch. They neglect to eat during the (roughly) one-month period spent taking care of their unhatched eggs, but apparently they do not die of starvation. A biological explanation of these short lifespans (or rapid ageing) is not agreed at present. One idea is that the lifespan is limited by the number of safe niches in their environment. If adults lived longer, they would use up all the safe niches. In that case, the baby octopus would scarcely survive. It is known that the same niches are used by generations of octopods. They are usually in the calcium carbonate reefs which were formed in tropical waters.