Final answer:
The discussed organisms are lampreys and hagfish, jawless fish that use their specialized mouths to feed parasitically by clamping onto live fish or scavenging dead organisms, respectively.
Step-by-step explanation:
The chordates known for their parasitic feeding behavior by clamping onto live fish are primarily represented by lampreys. These jawless fish have evolved a specialized toothed, funnel-like sucking mouth that enables them to attach to their hosts by suction. When a lamprey finds a suitable fish host, it uses this mouth to tightly adhere to the fish's body and then uses its rough tongue to rasp away at the host's flesh. This method allows the lamprey to feed on the host's blood and bodily fluids, making it quite specialized among parasitic organisms.
Lampreys are not the only chordates that exhibit unique feeding behaviors; closely related to them are the hagfishes, which are known for being scavengers. Hagfishes feed on carcases of dead fish, penetrating the bodies of their prey to consume them from the inside out. Both lampreys and hagfish lack true jaws, but they have adapted to their respective ecological niches to exploit available food sources efficiently. Lampreys primarily inhabit coastal and fresh waters, going through a life cycle that transitions from larval suspension feeders to parasitic or free-living adults. Lastly, some chordates like lancelets are suspension feeders, not parasites.
In summary, the parasitic feeding behavior described involves the organism attaching itself to live fish to consume bodily fluids and is characteristic of lampreys in their adult stage.