A: Anatomy

What is the anatomy of an immortal jellyfish?

As a multi-stage organism, the jellyfish’s anatomy changes through its life cycle.
Beginning as a polyp, the immortal jellyfish is formed as a polyp in a colony of such forms, called hydroids. These hydroids have stolons to connect them to their resident surface, and upright branches which bloom medusa buds, which eventually are released from the main colony.
The immortal jellyfish’s medusa form can reach an even 4.5 millimeter diameter, making a circular bell shape. This bell is made of a jelly, or mesoglea, covered by two layers of epidermis (like a peanut-butter jelly sandwich, minus the peanut butter). This mesoglea is somewhat thicker at its topmost part, and replaces a respiratory system in that the ‘skin’ of the jellyfish is thin enough for diffusion to deliver oxygen to the body. Also contained in the skin of the jellyfish is its nervous system, a kind of ‘nerve-net’ starting at the ‘rophalial lappet,’ the ring around the base of the jellyfish’s bell. This jelly-skin encapsulates a bright red, cross-shaped organ called a manubrium. The manubrium is a mixture of stomach and mouth, where a stalk protruding from the bell’s interior dangles down to a mouth at its base. The mouth opens into a gastrovascular cavity, which digests nutrients for the rest of the body. The smaller renditions of this creature have but eight tentacles, whereas the larger, older specimens have ten times that number.