Final answer:
Chordates that feed as larvae for several years and then mature, reproduce, and die within a few days exhibit a lifecycle pattern called semelparity. This pattern includes a single, often large, reproductive event, exemplified by species like the Chinook salmon and tunicates.
Step-by-step explanation:
The lifecycle pattern in question, where chordates feed as larvae for several years and then mature, reproduce, and die within a few days, is called semelparity. In semelparity, a species dedicates most of its resources to a single, often extravagant, reproductive event before death. One example is the Chinook salmon, which after spending years maturing and accumulating energy in the ocean, migrates upstream to spawn once and then dies shortly after. This lifestyles is in contrast to iteroparity, where organisms reproduce multiple times over their lifespan.
Other chordates, like tunicates, exhibit semelparous behavior. Tunicate larvae are free-swimming and possess all characteristic chordate features. However, once they find a suitable surface to attach to, tunicates undergo metamorphosis into a sessile adult form that lacks these typical chordate structures, culminating in a short reproductive period before death.