Chestbuster

Chestburster
The chestburster is the immature infant form of the xenomorph which emerges forcibly from the chest of its host, killing it. The chestburster is similar in form to the fully grown alien but far smaller and pale in color.

The chestburster was designed by Alien special effects master Roger Dicken. Giger had produced a model of a chestburster that resembled a plucked chicken and was far too large to fit inside a ribcage. Much to Giger's chagrin, his model reduced the production team to fits of laughter on sight, Scott drafted a series of alternate designs for the chestburster based on the philosophy of working "back [from the adult] to the child" and ultimately produced "something phallic," so Dicken was given the task to design it. Giger stated the finished form first resembled a dinosaur but the arms and legs were removed.

The chestburster in Alien 3 was far more developed, possessing complete limbs. The Queen chestburster depicted in Alien 3 has all four arms.