Spoiler Level: High
My apologies for the gruesome photo, but I couldn't let my review of the episode with the goriest scene in Star Trek history go without it. Credit also goes to Topless Robot's article The 15 Cruelest Deaths in Star Trek History, for saving me the trouble of doing the screen capture on my own this time. And in case you're wondering, poor Remmick here came in at #8.
But "Conspiracy" is notable for two other reasons as well. First off, it was the first time we got some kind of story arc in Star Trek, with this episode being a direct follow-up to "Coming of Age." And even though this particular story arc didn't go any farther than this episode, the concept of the arc as a story-telling device would become a regular staple on Start Trek from here on out, particularly with the Klingons on Next Gen and for much of Deep Space Nine.
And secondly, it showed that the producers were interested in coming up with new recurring villains, since the Ferengi just weren't fitting the bill. The Romulans were also brought back in the next episode, and the following season would introduce the characters that did finally become the main bad guys of Next Gen, the Borg.
I have no idea if the parasites were considered too dark or if once they came up with the Borg they just weren't interesting in following up on this story line. Either way, they were never seen again. Thank heavens for TrekLit-- the homing beacon mentioned at the end of this episode as well as the origins of the parasites are finally followed up on in the Deep Space Nine novels The Lives of Dax, Worlds of Deep Space Nine Volume Two, and Unity.