The Golden Mycelialgae are the result of the Binucleus Pseudo-Cyanobacteria being so receptive to horizontal gene transfer, obtaining a variety of new genes most visibly from Oilcons and Nitroadoras. Ironically, the sheer amount of hybridization has also resulted in the loss of high receptiveness to horizontal gene transfer. This has resulted in quite the monster of a genus.

Externally, Golden Mycelialgae cells are still clearly of kind of binucleid origin as shown by their twin nuclei. However, it is an unusual color not commonly seen in binucleids: orange. It obtained this color, along with an incomplete part of the silicone-forming genes, from its Oilcon parent. The detail that it is only an incomplete part is represented in that it never produces silicone—the pure silicon is almost immediately oxidized back into silica, which is deposited into the cell wall. From its Nitroadora parent, alongside motility for one of its cell types, it has obtained the ability to produce heterocyst-like chloroplasts; with these it is able to fix nitrogen, making it a diazotroph, and species which fix more nitrogen are more yellowish.

With its changes and evolution out of the way, we only just now reach the general biology and life cycle of this strange genus. The Golden Mycelialgae, as its name suggests, has an often macroscopic colonial form resembling mycelium. Many existing colonial dikaryotic binucleids have orderly colonies, but the Golden Mycelialgae lacks the specializations that allow this to occur. Like with Terran dikaryotes, its colony structure is therefore completely limited to a branching root-like form which is only one cell thick, as anything else would restrict its ability to ensure daughter cells receive the correct number of nuclei. The individual cells have cell walls made of cellulose studded with biogenic silica, the latter making it both heavier and more difficult to consume. When it comes time to reproduce, motile, twin-flagellated monokaryotic spores resembling an adora are formed at the tips of the colony’s branches. These cells have a single light-sensing organelle and swim flagella-first towards light patches, where they meet and fuse with other spores. When spores combine, an aspect of the primary ancestor’s original reproduction is represented, as their nuclei temporarily fuse to swap parts of their chromosomes before splitting from one another again. The dikaryotic zygote germinates into a colony right away.

There are many species of Golden Mycelialgae. Microscopic varieties, often invisible to the naked eye, can be found floating freely in the ocean and contribute greatly to the ocean’s phytoplankton. The most common macroscopic varieties are benthic, sinking to the seafloor as they grow and latching on by nature of their mycelial structure. However, they can also be found floating out in the open ocean; these species usually have less silica in their cell walls, making them lighter, though they still have enough to be resistant to being consumed by large filter-feeders. Some species also specifically grow on floating flora and pelagic fauna. As they use a wavelength of light which penetrates deeper underwater, benthic and free-floating varieties exist a little bit into the twilight zone; at the time they evolved, this included species which live on Rhino Ridge, weathering the volcanic conditions with a thickened cell wall while thriving on the dim blue light. The colony structure also varies between species, with some forming strands with very little branching and others forming elaborate “cotton ball” shapes which branch so much that they appear like soft, sparkling golden spheres. In general, larger colonies have more branching than smaller ones. In general, smaller species fix nitrogen far more than larger ones. The reason for the broad range of colony size, ranging from microscopic strands to comparatively massive tangled balls, is that the mycelium-like colony structure, lacking any cellular differentiation, is infinitely scalable.