The intestinal centifin split from its ancestor the centifin. The ghastly snarks ate so many centifins that some were bound to survive the digestion process. Those that survive adapted by having thicker exoskeletons which are resistant to the stomach acid of the ghastly snark. Once past the stomach the intestinal centifin will latch onto the intestines of its host. There it will suck the blood constantly. They have changed their reproduction to 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.