The centestin replaced its ancestor the intestinal centifin. Like its ancestor it mimics its cousin the echofin and waits to be eaten by the snarks and gharks. Once inside they will feed on the blood of its host. They no longer needed legs and just wriggle around once inside. Their jaws keep them anchored to the intestinal walls and are so strong that it would rip the intestines if one tries to pull them off.
They have very thick exoskeletons which are resistant to stomach acid. Once past the stomach They are asexual so they no longer need to find a mate to reproduce. As long as they find a suitable host they will eat and lay their spore within the intestine. Then the spores get "pooped" out and grow into little centifin-like creatures. These creature will get eaten up with the normal centifins and thus the cycle continues. If they don't get eaten they will starve and die.