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.

These aliens are enigmatic creatures, which have come to Earth for an unknown reason. However, it's entirely possible that they came to evacuate people from an evil threat to the entire galaxy.

Biology
As the name suggests, a Heptapod has seven limbs, whose arrangement makes the creature heptaradially-symmetrical.

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. They completely lack any surface features; there are no visible thrusters, nor are any emissions whatsoever detectable from these Shells.