Megaspawn

Megaspawns are large, bioengineered aliens from another dimension in X-Com: Apocalypse. Their are functionally organic weapon platforms.

Overview
Towering around nine feet (three meters) tall, a megaspawn is the most robust alien type that can be encountered inside of an alien ship. It's bulky frame is somewhat flesh colored, and crossed by many purple veins. Multitude of organic tubes and other cavities are all over it's body. Presumably these are exhaust pipes to protect inside organs from overheating.

The creature has no neck, or even hands. It's mouth is brutal looking with plenty of sharp, protruding teeth. It's functionality either never was to be for food intake, or it has become vestigial. It must be completely dependant on other aliens for nourishment.

Even though megaspawn are engineered to be organic weapon platforms, the weapons itself do not grow from a megaspawn. Weapons are later implanted into their flesh, but their nervous system is directly linked to their weapons.

It has utterly complex and unnatural organs, where it can actually grow the ammunition it uses - especially the dimensional missiles.

Role in invasion
Megaspawns are the heavy weapons of  extradimensional aliens. They aren't designed with intelligence in mind, and so require a guiding hand or a psionic command to carry out it's tasks. They are commonly seen in larger alien battleships, and guarding vital buildings in alien dimension.

Megaspawns are living tanks. It fires disruptor beams and extradimensional missiles that generate antimatter explosions where they hit.