Thrykar's species

Thrykar's species is a sapient, unnamed species of serpentine amphibious creatures. They are part of an interstellar culture that includes thousands of different races.

Biology
Members of this species are dark-skinned serpentine bipeds with sinuous bodies about 8 ft. long (~ 2.43 meters). Although they can walk upright, their legs are disproportionately short, and they move much faster when swimming. Extending outward from both sides of their bodies are triangular fins ribbed with cartilage. Four tentacles, about as thick as a man's thumb, function as manipulatory organs. These tentacles are evolutionarily derived from the cartilaginous side fins, and are not as strong as Human hands. Although there is no neck separating the body from the dome-shaped head, the lack of mobility of the head is compensated by a pair of independently-mobile eyes which are more than three times larger than Human eyes.

Members of Thrykar's species are amphibious and sleep underwater, although they can spend very long periods of time on land. They evolved on a watery world and can survive in Earth's environmental conditions without problem. Like Humans, they are a dioecious species with male and female individuals. Thanks to their larger eyes and smaller retinal cells compared to Humans, the eyes of this species can function as natural magnifying lenses and also move independently of each other.

Similarly to Humans and other species, the blood of Thrykar's species contains amoeboid defense cells known as leukocytes. Their diet includes food that contains dextrose.

Culture and society
Members of this species practice marriage and even go on honeymoons.

They have developed a complex medical treatment that allows them to modify their immune system, replacing the individual amoeboid leukocytes with a single unified "giant cell", which is spread through the entire body and linked with the nervous system in a way that allows the treated individual to have voluntary control over their physiology and regenerate from wounds, disease and old age, becoming biologically immortal as a result. However, the treatment requires them to regularly inject themselves with blood samples, taken either from other sapient species or from untreated individuals of their own species with a different blood chemistry, so that alien leukocytes are introduced to the treated individual's bloodstream and contact with them prevents the "giant cell" from degenerating and breaking up.

Appearances

 * "Assumption Unjustified", by Hal Clement (1946)