The details of their inner anatomy are mostly unknown, save for their 'Squeedilyspooch', which is mentioned throughout the series and is confirmed in the commentary of Germs to be one large super-organ, filling most of the Irken's torso An Irken's blood has never been seen in the show, but there have been some hints in episodes such as Planet Jackers (when he tried to distract them by fighting them hand-to-hand). After a while we see Zim again, but this time he is badly injured and his face is covered with patches of green liquid; presumably blood. Another good example of an Irken's blood color is any time he gets burned with meat like in Tak: The Hideous New Girl, when he returns home and we see him in GIR's point of view, smoking and covered with dark green patches (most likely bruises) on his face. Suggested at the end of Dark Harvest, when Zim was deemed 'healthy' by the nurse once she checked his thermometer, an Irken's body temperature may be very close to that of humans. Irkens have square cells
An Irken's skeletal system is almost similar in structure to a human skeleton, but more flexible, durable, and can regenerate and heal much faster. The skeletal structure of several Irkens can be seen in The Nightmare Begins
Although Irkens don't have any nostrils, they smell from the same area as humans; however, this reaction may be for comedic purposes for the show only. Either that, or there is a permeable membrane in that area which can detect scents.
Strengths and Weaknesses
Irken skin can kill parasites such as lice, possibly by secreting some sort of protective substance. However, while safe from such pests, their skin cannot tolerate Nuclear Chemicles. They are capable of regenatating body parts if severed and capable of travling at car speeds. the Irkens are also one of the most longes lived creatures in the entire universe. In fact It appears "Young Adult" Lasts from 140-10,000 years and "Middle Age" Starts at 160,000.
THe Irkens Have a Beedy eyes, dispite their apperence not compound. The bigger dot may be what is a pupil. They also seem to be sensitive to irritants: in The Nightmare Begins, Zim seems very agitated by his new contact lenses, complaining that they "are all scratchy" while desperately rubbing at his eyes. Also, in the episode Planet Jackers Zim actually loses an eye for a few seconds; we see that it is like an oblong sphere in shape and attached to a long, thin cord of sinew and muscle, which might be the equivalent of the optic nerve. As Zim simply replaces his eye by pushing it back into its socket a moment later with no signs of distress or loss of function, it could also be theorized that the Irken eye is an artificial implant of an unknown nature; an unaired episode, Day of da Spookies, implied as much; yet, in a flashback scene in the episode Parent Teacher Night which apparently shows Zim's "birth", he clearly has eyes in his head The majority of Irkens have red, green or purple eyes with red being the most common, followed by purple, dispite this the eyes are every color.
Genders and Reproduction
Irkens apparently have female and male Genders, Female Irkens appear to have different shaped antennae from the males (slightly curled), and more pronounced eyelashes, on average they're slightly-shorter than the males. the species reproduces through cloneing
The IQ of the Avarage Irken is 9,000, however the Irken Sciencetist IQ is about 17,647, Even more intimating the Most INTELLIGENT Irkens have an IQ that is about NEAR-INFINITY, The entire Species is aware if the past is altered at a massive scale, meaning they are aware of Quantum activity. In the Basic terms They would make someone like Jimmy Neutron Look like a complete idiot.
Irken babies, who are created in a large "birthing facility" beneath the surface of Irk. When they are two minutes old, they are given a name and They don't come out with many teeth accepted maybe 1 or 2,they then hit their growth and begin to develop their full grown teeth
Avarage Height and weight
with a minor exceptions of service drones (1,7 ft), fry lords(7 ft), and the Almighty Tallest(8,11) although with some slight differences in size the avarage population stands about 4,5 ft. However the weight is unknown however there usailly Light to Medium weight