List of unidentified species

The following are a list of evidence and appearances of potential numerous alien species that have not been identified or named in the universe

Other Sources
Confirmation other species exist: Canon Fodder: Bulkhead Banter

CHeeeezyy: Are there any other kind of sentient beings (as like if they knew how to make tools and stuff) in the Milky Way galaxy?

''A: The short answer is yes, the Forerunners indexed and reintroduced many sentient species into the Milky Way galaxy. The longer answer is that only a fraction of these species have gone on to build tools or achieve even Tier 7 (preindustrial) signature technologies in the millennia following the firing of Halo; of those, only a handful have been encountered by humanity in the Orion Arm region of the galaxy. In fact, not even every species that fell under the yoke of the Covenant have been contacted and catalogued by the UNSC, as the Prophets did not deign many worthy of trading service for salvation within their fleets and the Sangheili kept few records of civil affairs.''

Number of catalogued species: Halo Silentium - Page 18

"But as Catalog I am aware that she has studied and favored one hundred and twenty-three technologically capable species across three million worlds within the explored regions of our galaxy. How many of these she will seek to preserve, it is not my job to predict or even to understand."

At least a total of 123 sapient species existed in the Forerunner ecumene

Installation 04 (Alpha Halo)
Below is evidence of alien species arriving at the Halo installation Installation 04.

Crashed ship
Around 40,000 BCE after the firing of the array, during an experiment 343 Guilty Spark conducted on the Halo, an Unidentified alien vessel crashed on the ring. However none of the species left the ship or attempted contact, and Guilty Spark built a sarcophagus around the vessel. Ultimately Guilty Spark was hopeful for the next species to arrive on the ring.

Visitors to the ring
During the Battle of Installation 04, 343 Guilty Spark noted in logs made during the battle that the Covenant landing on the ring and seeking something was similar to other alien species who arrived at the ring who recorded what they saw and left. These visits ultimately lead to 343 Guilty Spark changing from being hopeful at meeting alien species, to threatening ships that went near the ring, this persisted until the arrived.

Installation 05 (Delta Halo)
Below is evidence of alien species arriving at the Halo installation Installation 05.

Flood outbreak
It is suggested that there was potentially outside meddling that lead to a Flood breach at the containment facility, leading to an outbreak and eventual formation of a Gravemind on Installation 05.

Installation 07 (Zeta Halo)
Below is evidence of alien species at Halo installation Installation 07.

Banished occupation
During the Banished occupation of Installation 07, an alien called The Harbinger, and aliens known under Skimmers were present.

System of Miasmic Giants
Below is evidence of alien species around the System of Miasmic Giants.

'Crecka's survival
Unknown Species: Broken Circle - Page 30

''The old warrior rubbed thoughtfully at his scarred eye socket. "Many cycles ago, I was the last survivor of a vessel brought down by hostiles - we never knew what race it was. They did not speak a civilized tongue. All this was on the far side of the galaxy from here, in the System of Miasmic Giants."''

This is a species that nearly destroyed 'Crecka's ship in the System of Miasmic Giants.

Line Installation 9-12
Below is evidence of alien species at Line Installation 9-12.

Crashed ships
Unknown ships 2: Halo 4 Wreckage Map

Unknown ships appear around Line Installation 9-12

Netherop
Below is evidence of alien species on the planet of Netherop.

Spider mechs
Halo Oblivion - Need to expand

Unknown Location
Below is a list of alien species in unidentified locations.

Solitary
Prisoner: Halo Reach Map Solitary

A prisoner escaped from this location