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The hosts of its ancestor, Protohydroia Octherma, accumulated on the chitinous surfaces of dead Tudeeps like moss on rotting logs. Over time, the tudeeps' thick, chitinous cells would be decayed by Melter Detritis, or opened up while they were still alive by disease-causing Protopathogena crysta. Some Protomancerxia thermaparasitica pierced through the thoroughly-decayed chitin layers of tudeeps while feeding on their typical hosts.
The fungal mush of a tudeep eroded by the heat and acids of a hydrothermal vent was much more nutritious and abundant than a single Protohydroia Octherma. Over millions of years, some of the parasites adapted to take advantage of the resource, growing longer, thicker feeding tubes, like plastic straws.
While dead tudeeps cannot regenerate, unlike a host Protohydroia Octherma, their sheer size and the Saprobe Protomancer's pace of consumption means it can take months to drain a Tudeep, if no voracious detritivores get there first. Since the Saprobe Protomancer doesn't need to select a new host in its lifespan and one individual can easily share a dead Tudeep with its descendants, its support-tentacles of cell membrane are thicker, heavier struts that allow it to clamp onto the ragged edges of a hole through the chitin of the tudeep.
Occasionally, they feed on dying Tudeeps as well, whose chitinous shells are thinned by disease and cannot dissolve microbes so well.