These are unidentified non-humanoid species observed in the 23rd century.
Bird-like creature
A bird-like creature
An Avian looking creature was displayed at Trelane's mansion. (TOS: "The Squire of Gothos")
Multi-eyed Alien
A multi-eyed alien
A painting with a member of this species with many small black eyes underneath two large eyes hung in Dr. Leonard McCoy's sickbay aboard the USS Enterprise for some time. (TOS: "The Enterprise Incident", "That Which Survives")
A space-borne lifeform vaguely resembling this painting was encountered by the crew of the Enterprise in the first issue of the non-canon comic Star Trek: Early Voyages. The resemblance was probably coincidental.
Yellow creature
A yellow creature
In an alternate reality, one young Vulcan was studying the image of a yellow creature, which moved as if it was either flying or swiming, inside a learning pit. (Star Trek)