The mass of tissue is soft, and yields too easily to the touch. The surfaces are covered in complex ridges, like the gills of fungi. There are sometimes slowly contracting holes, places where the ridges have been pushed apart by something emerging. The mass is largely unaffected by bullets, but area-of-effect weapons, explosives and disassemblers are very effective. Inhalation of particles blown off by weaponry will invariably infect the unfortunate inhaler.
Crèche is a biological strain, infecting biomorphs and pods.
Stage 1: (Initial infection to one month) In the early days of infection, the only symptom is an increased appetite. The victim will begin to gain weight, but not as fat. A new type of tissue is growing throughout the victim's body: a fibrous, pseudo-fungal network grown from hijacked lymph nodes. The infection can only be diagnosed with a tissue sample or detailed medical scan.
Stage 2: (One month to two months) Once the infection has infiltrated the victim's brain, and built a sufficient store of energy and nutrients, it will induce a nesting compulsion in the victim. They will gather as much organic material as they can manage, piling it into a hidden niche. When they are satisfied that they have enough, they will burrow into it. The infection will no longer maintain its host's body, using it and the gathered organic matter as it grows. The growing flesh is a pale, off-white globe, with ridges and valleys tracing its surface.
Stage 3: (Two months+) Once a critical volume (not mass) is reached, the flesh has become a crèche. A simple, but powerful genetic computer, it endlessly recombines the genetic material of its former victim. Any of these combinations that prove viable are gestated, slowly moved from the center of the crèche to the periphery and expelled once mature. The behavior of the beings, like their anatomy, are not consistent, except for basic instincts not to harm the crèche and to bring it organic matter.
Left alone, a crèche's expansion will be limited only by the volume of it's environment and the amount of organic matter it can absorb. A very mature example might fill every square centimeter of a ship or station, packed with the unborn, waiting for there to be enough room for delivery.