The Hivemind Necromorph Type Explained (Dead Space Remake Lore)

Gameplay credit: Gamer's Little Playground -    / @glp  

The Hive Mind was a massive Necromorph variant created by Marker 3A on Aegis VII.
It was unwittingly created by the Sovereign Colonies, as a result of military testing of the experimental Marker 3A on Aegis VII in the 2290s, and acted as a nexus between the Marker and the rest of the Necromorphs. The Marker maintained its connection to the HiveMind through a signal-amplifying pedestal, which it used to relay orders to the massive creature.
The SCAF eventually aborted any further experimentation with the Marker, sealing off Aegis VII and abandoning the artifact somewhere above the Hive Mind's resting place beneath the surface where it remained for the next 200 years.
The Hive Mind resembled an enormous worm with tentacles along its length. Its full size was never truly shown as an unknown portion of the creature was hidden inside the crater, but it appeared to have a defined head and thorax. It is unknown how many bodies were used to create the Hive Mind. The creature had a very fleshy appearance on its lower thorax, almost resembling human skin with muscle tissue covering certain areas, and its tentacles appeared to grow from well below this thorax area.
The head's most prominent feature was a massive circular mouth, consisting of two sets of jaws, each with their own rows of teeth. The Hive Mind was able to spit acidic pods from its central mouth. Around the mouth, there were five quote-unquote “eyes” made from yellow explosive fluid. The thorax featured a frontal cavity which sheltered five more yellow sacks that served as the Necromorph's vital organs with a rib-cage serving as protection for them. The back of the creature featured several branched, antenna-like appendages; the purpose of these was unknown, but it is possible that they served as antennas helping in broadcasting the Marker Signal to other beings as well as forwarding commands to the other Necromorphs.
The Hive Mind acted as an organic 'command centre' for the Aegis 7 Necromorph outbreak, as Marker 3A referred to it as a "nexus" between itself and the Necromorphs.
The connection between the Hive Mind and the Marker was strengthened by the Marker's Pedestal, which amplified its signal and allowed it to relay orders to the creature. When the Marker was removed from the pedestal, the connection was severed and the Marker could no longer coordinate with the Hive Mind.

A Nexus organism is the name given to Necromorphs that are able to broadcast the signal from the Markers and Brethren Moons to the smaller Necromorph variants.
Another of this type was the Nexus seen on Tau Volantis, and which served the same purpose of the Aegis 7 version, except instead of being made from the combined biomass of thousands of Humans, the Nexus was made from a single gigantic Tau Volantian, as the alien species had an indeterminate growth, meaning they would continue to grow throughout their entire lifespan without stopping.
The Boss from the mobile game is thought to be an immature Hivemind; and both the Ubermorph and some Slashers which have the same 5 eye layout are speculated to also be some sort of progenitors of the Hive mind type. Perhaps as a new Hivemind begins to form, one of these would act as the dominant Necromorph to which others would then assimilate into.
The Hivemind will use its tentacles to Slam down onto its enemies, and will also use them to grab with so it can devour them. It can also spit out explosive sacks and smaller Necromorph forms.
200 years after the Sovereign Colonies abandoned Aegis 7; the Concordance Extraction Corporation mining company discovered the planet and found out that it was a goldmine of resources. Regardless of the restrictions for traveling to the Aegis System due to the classified information regarding the First Aegis VII Incident, the CEC decided to construct an illegal mining colony on the planet to begin harvesting it.
A a small team of miners found the Marker. Immediately upon its discovery, it began the first phase of the second Necromorph outbreak by slowly driving the members of the mining colony insane. As the Ishimura arrived at the planet, the colony began the extraction.

As the colony was overrun, the Ishimura followed as both the Marker and the infection were brought on board the vessel. In a matter of hours, both the colony and ship were lost. Dr. Kyne recovered footage of the Hive Mind during the outbreak, and the crazed Dr. Mercer came to learn of its existence and turned to worshipping it as a divine entity. The Hive Mind appeared to be the controlling intelligence of the Necromorphs in the Aegis VII System.
With the absence of Marker 3A's creators preventing Convergence from beginning, the Marker instead sought to imprint its codes After the USG Kellion arrived at the Ishimura, the Marker seemingly encouraged Kyne to request the assistance of one of the Kellion's crew, a CEC engineer named Isaac Clarke.