Tudeep
The tudeep photosynthesizes using a chemical similar to the bacteriochlorophyll of Earth's green sulfur bacteria. It absorbs bands of red (650-680 nanometers) and near-infrared light, emitted by the dim glow of some of LadyM's fiery vents. Like green sulfur bacteria, they use hydrogen sulfide, rather than water, in their photosynthetic processes, and produce elemental sulfur, rather than oxygen, as a byproduct.
Between the low light levels, extreme conditions, and low food supplies (as of the time it evolved) the tudeep grows slowly. It can take about three (Earth) years for it to reach 50 cm, the typical age it is capable of reproducing. Yet, individuals continue to grow slowly past then; some individuals reach 70 cm. Partly because of its slow metabolism, it can live a rather long time for crystalflora of its time: about 50 Earth years.
The tudeep is not quite as tolerant of heat as Octherma. Spores that germinate on patches of seafloor that are too hot or acidic fail to germinate. Spikes of heat or acidity cause even established individuals to rapidly die, which is why few tudeeps even reach their maximum age. However, the tudeep struggles to survive if too far away from life-giving heat and light. Due to their delicacy, they make a distant ring of "standing stones" demarcating habitable temperatures around a vent.
The tudeep's fungal core produces a broomstick-like bundle of "roots" under its crystal. These roots have thin coats of stiff, sclerotinized chitin, which at times crack or distort under adverse conditions. The roots of the tudeep have a vague resemblance to bent, petrified caterpillars. While the fungal parts digest organic matter laying about, it also outright scavenges, or digests weak organisms alive.
Protohydroia Octherma colonies may grow on their surfaces, but enzymes emitted by the tudeep's fungal core slowly digest them. Yet, their production of elemental suflur, one of the Protohydroia Octherma's foodstuffs, encourages them to grow nearby anyway. Protohydroia Octherma encrust dead Tudeeps, to the point one vent-facing side may be entirely encrusted with octotherma, almost like a tree with moss pointing north.