Species / Legends Species were unique lifeforms . They were generally divided into three classifications based on their level of sentience : sentient , semi - sentient , and non - sentient . There were over 20 million sentient species known to the galaxy . Sentient species were sometimes erroneously referred to as races , which more accurately referred to groups or subspecies within a species . Lifeforms . The five characteristics of lifeforms were organization ( a distinct form and appearance ) , irritability ( the ability to respond to external stimuli ) , metabolism ( the ability to convert energy to stay alive ) , reproduction ( the ability to create new lifeforms ) , and adaptation ( the ability to change as their environments change ) . The predominant form of sentient life in the galaxy was carbon - based lifeforms . However , other forms of sentient life did exist , such as silicon - based or energy - based lifeforms . Reports from remote parts of the galaxy even mentioned giant clouds of interstellar gas which had evolved a form of intelligence based on internal force - fields . Across all species , the majority were oxygen breathers , although a number breathed other substances such as ammonia , cyanogen , methane , methanogen , helium and Dorin gas . Despite these differences , most species were easily classified into a number of distinct categories : Mammalian sentient species were warm - blooded vertebrates , who nourished young through secretions from mammary glands . Most mammals were covered in hair . Some of the most prominent species in the galaxy were mammals , such as the Humans and their numerous offshoots , and the Duros . Other notable forms were Wookiees , Cereans , Bothans and Sullustans . Reptilian sentient species were cold - blooded vertebrates , typically covered in scales or bony plates . They typically evolved from species such as lizards , snakes and crocodiles . Most reptiles were land based , and lay eggs to reproduce . Reptilian sentient species were also very common in the galaxy , and notable examples included the Rodians , Barabel s , Chistori , and Trandoshans . They also came in less humanoid forms , such as the Slith and Ssi - ruu . Plant sentient species synthesized energy from water , nutrients and sunlight . They were usually immobile , although some species were able to move to seek better soil , light or nutrients . The Neti , Ergesh , Revwien s , Zelosian s , and Sylphe are some examples of this form of life . Insect sentient species were arthropods , with defined body segments ; most commonly head , thorax and abdomen . Many had hard exoskeletons and wings , and could have any number of segmented legs . Some insectoid species evolved into different forms , such as humanoid insect species . Common examples of this form of life were the Verpine , Fefze , Killik , Bartokk , Gand , and Geonosians . Hard invertebrates had hard outer bodies with no internal skeleton . These often included crustaceans and some flying creatures . While this classification also included insectoid species , they were grouped separately . Examples of hard invertebrate sentient species included the Sauvax , the Aganof and the Tarc . Soft invertebrates were descended from soft - bodied species with no bones , such as octopi , slugs and worms . Sentient species of this origin took many diverse forms , such as the Iyra , Hutt and Ee . Avian sentient species were warm - blooded , feathered and winged creatures . They typically had light bones and strong muscles , needed to enable flight . However , many sentient avian species had lost the ability to fly . Examples of this kind included the Vor , Mrlssi , Quor ' sav , Rishii , S ' kytri and the Tikiarri . Aquatic sentient species were those descended from marine life . These lifeforms often fit into other categories , but were classified together . Aquatic lifeforms included those that could breathe water , air , or both . These include the Mon Calamari , Selkath , Nautolan , Quarren , Herglic , Vurk , Dellaltian and Gungan . Craniopod sentient species were , despite these broad categories , lifeforms so truly alien that they did not fit easily into any of the common categories . These were categorized as exotic sentient species , and included the Bith . , Celegian s , the Filar - Nitzan and the Pulra . The study of sentient species . Many institutions in the galaxy focused on the study of sentient species . The most notable were the University of Coruscant and the University of Sanbra . Those scientists and anthropologists that studied sentient species were known as sentientologist s . One of the major works on sentientology , Obo Rin ' s " Catalog of Intelligent Life in the Galaxy " , was commissioned by Lord Vader , and was carried out under the auspices of Major Vontenn , Liaison Officer of Sentiology Studies . While it contained much information , it was also a conduit for Imperial propaganda , and as such , had a tendency to depict some species as less developed than was actually the case . Rin ' s credentials as a scientist were also questionable . Another major work on sentientology was " The University of Sanbra Guide to Intelligent Life " by the Iyra Tem Eliss . Rather than a scientific study , it was designed to facilitate first contact with species , providing " guidelines as to common cultural interests , goals , fears and drives . " However , it departed from Imperial doctrine on a number of points . The Empire tried to apprehend its author shortly before publication , but the academic escaped and released his research through underground networks and NewsNet s . The Shi ' ido researcher Mammon Hoole wrote the acclaimed " The Essential Guide to Alien Species " . He gained unique insights into species by infiltration using his shapeshifting abilities . Other documents that detailed sentient species included the " Universal Encyclopedia " . Behind the scenes . Species in the " Star Wars " universe generally have a large compatibility to real - world classification systems . However , these are not always strictly adhered to . For instance , according to " The Essential Guide to Vehicles and Vessels " , the Colossus wasp s " follow the standard insect physiognomy , with a head , thorax and abdomen , " which corresponds with the real - world physiognomy of insects ; however , the Sic - Six , which also have these three body segments but eight legs , are classified as arachnids , which in the real world have only two body segments . " Star Wars " also has numerous examples of species sharing characteristics from different classifications , such as the Quor ' sav species . They have a combination of monotreme — mammals that lay eggs — and avian characteristics .