The bloodworms don't get discussed because they just aren't very interesting. Frankly, the horror aspects of the episode were undermined totally for me when Nick Cook's character got eaten. Once he was still screaming after his lungs were clearly gone the whole scene teetered into unintentional comedy. It was impossible for me to take the worms seriously after that.
Some would argue I'd do a far better job without lungs.
And I'm not sure the bloodworms even make sense from a scientific point-of-view. They're just a plot device for the Alex-Peter story.
There's a catalogue of plot points throughout Star Trek history that don't make much sense from a scientific point of view, so that's hardly anything new.