Nameks are a genderless alien race (from the animes DragonBall and DragonBall Z), usually found on their home world of Namek/New Namek, although they aren't above adventuring into the farthest reaches of the universe, even appearing in Rhy'Din on occasion. All possess a range of magical or ki abilities, which vary according to their caste. Most Nameks are telepathic to some degree, and due to their flexible physiology, they tend to be agile fighters. They possess some very advanced technology but choose to live simply, regardless of their location.
The Nameks are not a populous race, on account of a natural disaster on their home world many years ago. It wiped out the entire younger generation and a large portion of the elders. As a result, there is a large age gap between the eldest of the species and the general population. One Namek, Guru, was responsible for the majority of the Namekian re-population, and as the eldest and leader of the Nameks prior to his death, he has taken on an eternal grandfather role for the entire race.
Perhaps because of the asexual egg-based reproduction, Nameks don't seem to display typical familial relationships. Due to a very long lifespan and the ability to have many children in a relatively short amount of time (no pregnancy period), many Nameks are closely related. They tend to treat all members of their generation as siblings and don't appear to have an individual father figure, other than Guru.
Nameks are divided into two castes, apparently at a young age. It is unknown whether the caste is selected based upon the individual's abilities, or if the abilities are developed based upon what caste they join.
Those who enter the warrior caste develop extremely powerful combat abilities. Nameks are able to enlarge their limbs or even their overall size, which can be useful in close range combat. They also possess superhuman strength, partially because of their ability to manipulate ki. They are very adept at ki attacks, which can range from a simple energy blast to a large "beam cannon" shot from the fingertips. Some are even able to shoot concentrated ki beams from their eyes, like lasers. All Nameks possess the ability to fly (bukujitsu).
The sage/healer caste has a much broader range of ki abilities, but their physical ability is very limited. Even their ki has very little destructive power. They can fly like anyone else and possess potent healing ability. This ability is critical in major battles—even though Nameks are able to regenerate tissue, their ability to do so depends entirely on how much energy they possess. If they've been expending a lot of energy on ki attacks and even strenuous physical combat, their regenerative powers become much less effective. The sage class is also capable of creating objects apparently from air. This includes simple objects like clothing (warriors may be able to do this as well), but also things as complicated and powerful as Dragon Balls. Sages are extremely intelligent and are likely responsible for the technologically advanced spaceships used by the Namekian race.
Nameks (or Namekians) display a few traits similar to slugs (namekuji is the Japanese word for "slug"), such as their antennae and debatable hermaphroditic physiology. While no one has been able to study a Namek closely enough to determine whether or not they possess male, female or no genitalia, Nameks usually take on a male-like appearance (including deep voice) but reproduce by spitting out eggs, like a female. However, despite their namesake, the similarities between Nameks and slugs end there. In actuality, the organism Nameks most resemble is not part of the animal kingdom at all, but of the plant kingdom. A Namek's skin is predominantly green, with yellow arm markings. The markings are banded with colors ranging from pink to orange to red—the hue changes with age. Nameks only ingest water, and their home planet has three suns, eliminating night. As such, it is very likely that Nameks draw energy from photosynthesis, chlorophyl being the reason behind their skin color, just like a plant. They are also capable of regenerating body tissue, even an entire limb or body part. This is a common ability of plants, although several animal species display regenerative capabilities as well.
Unlike slugs (but like some plants), Nameks produce completely asexually. They do this by spawning eggs, usually one at a time. The offspring isn't actually a clone of the parent, as asexually reproduction might suggest—the parent can actually control the offspring's physical traits by manipulating the DNA they pass to the egg before spawning. All Nameks possess the same basic characteristics, however: the coloring, markings and antennae mentioned above, as well as large, elf-like pointed ears. (They have very sharp hearing.) All Nameks are bald, perhaps to maximize the area of exposed skin for photosynthesizing.
Nameks speak the Namekian language, although it appears that many, if not all, can also speak common English as well. It is possible that their natural telepathic ability is the reason for the widespread mastery of a second language.
Namekian - Wikipedia
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Official DragonBall Z Website
Note: Much of the information above is adapted from the anime and Wikipedia. However, this entry does contain original research and speculation, particularly that regarding the physiological similarities between Namekians and plants. Those theories are the intellectual property of Picc and should not be considered DragonBall or DBZ canon.