There is a life-form.
It comes from a world light-years away from ours, but many things about it are curiously familiar.
The life-form is an exact alien analogue of an Earthly vertebrate, with an internal skeleton covered by muscles and skin. It has an articulated spine, a bony casing to protect its brain, and four jointed limbs attached exactly like ours. There are five digits on each of the forelimbs; we are not certain about the hind limbs.
It lives on land, and breathes oxygenated air (using lung-like organs, to judge by the expansion and contraction of its upper body). The body-plan matches that of an anthropoid primate precisely. It is bipedal, and like apes it has lost its tail. The texture of its skin is very mammalian, and it appears to have the same bizarre distribution of hair as humans: very little on the body, a lot on the top of the head. (The location of other patches of hair is poorly documented.)
The large head has a jaw with opposed sets of teeth; two spherical eyes with irises to control light input; two ears, and a nose with two nostrils. Vision and hearing are strong, and the creature is diurnal. It is easy to mistake this life-form for a human, so eerily close is the resemblance. The unusual, pointed shape of the outer ear is often cited as a difference, but it is not clear if this falls outside the range of historical human variation.
There are differences in biochemistry. The life-form’s blood uses copper-based haemocyanin in place of our iron-based haemoglobin. Remarkably, they have been known to interbreed with humans. In spite of their extraterrestrial biochemistry, which surely ought to be incompatible with ours, viable young have been produced. One rose to fame as an officer on an exploration ship; I myself am a great admirer of his work.
These beings are highly intelligent, with a technological civilisation slightly in advance of ours. Like us, they wear clothing. Their material culture is alien, but not shockingly so. An odd cultural quirk is their utter suppression of emotional expression in favour of logical thought. This trait arose within recorded history, as a philosophical response to a series of devastating wars
There is a life form.
It is a predator, and a very successful one, widespread on its homeworld.
The being has several eyes, but its vision is surprisingly poor. Instead, it perceives the world mainly through vibrations in solid objects, to which it is exquisitely sensitive.
There are other oddities. Our creature breathes air using modified gills on the rear of its body. Some varieties have iron-based blood like us, but others have copper-based blood like our first life form. It has no bones. Body and limbs keep their shape thanks to a thick, segmented, semi-rigid skin that is similar in composition to our fingernails.
The life-form has a waist but no neck. It has six pairs of limbs. One pair are specialised organs of touch. Another is for stabbing into prey to inject a potent venom. The life-form then uses the stab wounds to drink the liquefied contents of the victim’s body cavity.
The remaining limbs are legs, though the hind pair are capable of such delicate work we could also call them “arms.” For this creature is a great builder. Using smart nanomaterials secreted from its own body, it constructs huge and elaborate traps. These often have an eerie geometric elegance that seems to indicate intelligence. In fact, the creature works entirely by instinct, though it has a knack for adapting its blueprint to different environments.
They cannot interbreed with humans.
There is probably one in the room with you right now.
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