Heptapod

Heptapods are an intelligent, space-faring extraterrestrial species in Story of Your Life and the 2016 film Arrival. In both works, their first contact with humans and Dr. Louise Bank's struggle to communicate with them serve as the plot and are used to explore themes about determinism, language and the Sapir-Whorf Hypothesis. Two heptapods, nicknamed Abbott and Costello, attempt to communicate with Louise and Ian from their ship in Montana.

These aliens are enigmatic creatures, which have come to Earth for an unknown reason. However, it's revealed that they are benevolent beings, whose ultimate goal is to unite humanity as they will need the humans' help in the far future.

Biology
As the name suggests, a Heptapod has seven limbs, whose arrangement makes the creature heptaradially-symmetrical. As seen in the film, they never leave the confines of their spaceships, perhaps due to them being unable to breathe Earth's atmosphere, and instead leave it to the humans to initiate first contact.

In the film Arrival, the Heptapods are depicted as having jointed, arthropod-esque limbs, each ending in a point that can split open into a seven-pointed starfish-like "hand". When walking they appear to put five limbs ahead and the remaining two behind as they move. They have a dull-grey, fleshy-looking skin with a rough texture, and they seem to have no visible eyes or mouths (though several orfices are faintly visible on Costello's upper body). Their appearances seem to vary noticeably between individuals, as Abbott is taller and thinner than Costello.

While most of their physical features are obscured for most of the film their full appearance is seen when Louise is taken into the ship by Costello. It is revealed that their seven appendages only form a small lower portion of their body, with a large upper section that resembles the diamond-shaped body of a giant squid, and a head-like protrusion at the top. Seen in silhouette, the upper body of the heptapod resembles a vaguely humanoid figure, eerily reminescent of images of a hooded Grim Reaper.

Communication and language
Heptapods use vocal communication that is unpronounceable by humans (classified as Heptapod A), and a written script (Heptapod B), which by its modularity can be dissected and interpreted. The vocal and writing components are unrelated, in the sense that Heptapod B does not represent sound. Heptapod B is written with an ink-like substance, and it can induce a non-linear perception of time unto those who intimately learn and understand the language.

Technology
Heptapods are more capable than humans when it comes to spaceflight. When they first contact with humanity, they use radio to transmit their vocal recordings.

Ships
Heptapod ships (referred to as "Shells") are 450-meter-tall vehicles composed of a black, stone-like material of unknown composition, and are oval and somewhat flat in shape, resembling an immense, obsidian concave lens. They completely lack any surface features; there are no visible thrusters, nor are any emissions whatsoever detectable from these Shells. There is, however, a small vertical corridor leading to a transparent glass wall, through which the humans communicate with the heptapods.

The interior of the ship is made of a white, glass-like material with a serrated texture. The inner atmosphere (presumably the atmospheric conditions found on the heptapods' homeworld) is thick and misty, and is dense enough to have properties between a liquid and a gas. Through this medium the heptapods can fly through the air, and project their inky logograms within the mist, and Louise was able to survive for several minutes in the heptapods' environment.

The ship is also able to send out a small, twelve-foot-tall cigar-shaped craft, which emerges from an unknown opening. Costello uses this craft to bring Louise into the ship.