Medusae - Anatomy and Physiology: The true horror from a Medusae is not due to the creature itself, for while it is clearly an unnatural creature, it does not seem to pose any direct threat. A Medusae's main body is no more than a bag of flesh, not much larger than a human head. The flesh itself is not unusual, except for the fact that it carries an unusually dense concentration of neural pathways and receptors. Some Imperial savants theorise that this unusual neurology resembles the brain of a sentient species, but most knowledgeable Magos Biologis wave off such thoughts.Its eerie hovering, though, is perhaps the most disturbing feature. While several savants have studied the creature, none can determine how it floats effortlessly without any visible means of propulsion. While the Medusae has no limbs as such, it does have a surprising number of thin, whip-like tentacles, numbering in the dozens. They seem to look like bare spinal cords, free of bone or chitin. This is not so far from truth, as the Medusae's main form of attack seems to be inserting these tentacles into the brain and central nervous system of a creature and melding with it. The Medusae has somehow become the ultimate parasite. It does not just live off of the vital fluids or flesh of its host. It actually becomes one with it.The Medusae's unique neural structure allows the foul xenos to insert itself into the mind of its host and take over the host's body, all the while allowing the host to remember and feel everything. Those few victims who have survived an encounter with a Medusae tell tales of feeling as if they can take in all of the emotions around them with exceptional clarity. Others have mentioned that they felt as if they were storing that emotion, intensifying it and holding onto it like an obscene sponge. Worse, those attempting to rescue their victimised comrades from the creature are often struck senseless by overpowering waves of powerful anguish, seemingly emanating from the very eyes of those they would save.Along the sides of a Medusae's body are also a series of thicker tentacles, often sprouting larger growths. These growths form in a series of ploin-sized tubers, folding over one another like a cluster of ripe fruit. The body of the Medusae seems to have no need for these growths and they appear to be completely extraneous to the Medusae itself. There are even reports of these growths coming off the Medusae during an attack without causing the creature any real harm, like the tail of a lizard. It has been noted, however, that as the creature attacks and uses its host, these growths seem to enlarge and new tubers seem to form.Studies of these growths have been inconclusive, though this has not prevented Cold Traders from doing a brisk business in them. They feature in tales of sordid gatherings where the debauched and debased dare each other to actually consume these growths. Even the smallest nibble is enough to send these foolish cads into paroxysms of either agony or ecstasy, it being difficult to tell the difference in their faces. The experience is too much for even these jaded degenerates, as they collapse into coma-like states, their brains unable to process such intense emotional power.Spire-gossip says that none have ever recovered, but this has not stopped others from such temptations, such is the reputation for the experience. Scholars of xenos in the Koronus Expanse are stymied by what little information there is about these creatures and how contradictory the reports appear to be. This has hindered efforts to pin down their homeworld, and many hold they are not native to the Expanse.The creatures do not seem to favour any one climate and, other than their attack upon victim sentients, they do not seem to require any sustenance, assuming this attack is indeed needed for survival. They have been sighted in the company of Drukhari raiders, latched onto what appear to be slave-caste beings, leading some to believe the creatures could be pets or even a food source for that foul xenos race. Some psykers have also provided accounts saying they had encountered Medusae whilst in states of dreamlike meditation, but the very nature of these reports make them dubious at best.