A Hhortah is probably based off a creature from an early episode of "Star Trek, the Original Series" (s1e25, "The Devil in the Dark"). It is a silicon-based life form in the shape of a blob, and spits out extremely corrosive acid with a high enough ph to cut tunnels through the hardest metals. In the show, it's spelled "Horta."
This certainly isn't the first "trekie/sci-fi" easter egg to be found in Spiderweb Software games...