One of my fictional planets (which is largely terran in nature) is notable for an unique animal. Said animal is a dangerous predator that is notable for several things:
- It is physically separated into three parts: one "hunter", one "digestor" and one "reproducer". All three parts share the same DNA and arise from a single egg and yet have individual circulatory systems and lungs. Only the hunter is mobile while the other two parts are largely static.
- The hunter's body contains a mouth and a pouch for storing prey, where it is only "pre-digested" (if at all). Other than that, it has eyes, feet, claws, teech and everything else a successful predator requires.
- After hunting, the hunter returns to the nest and gives the prey to the digestor, whose body lacks eyes and an ability to move. The digestor basically consists of one giant stomach rooted to the ground with deformed appendages.
- To eat, the hunter returns regularly to the digestor and harvests a nutrient juice through a separate, smaller "mouth".
- The reproducer is a modified digestor which uses its stomach to grow eggs before dying off.
- Only the digestor has a well-developed liver and kidneys. In turn, it lacks a large brain (the hunter has it).
While a process of "evolutionary assimilation" is presumed to be the origin of chloroplasts and mitochondria, the formation of a creature like described above is certainly the result of a reverse process, in which an animal's organs are separated from its body and become semi-independent in their function while de facto staying parts of it. All three parts - the hunter, digestor and reproducer (and any arbitary additional "castes") are dependent on each other in the long term, as most vital organs are "separated" among them.
The only organs every part will have will be those required for immediate survival. Among the already mentioned circulatory systems (with individual hearts, of course) and lungs, each part would probably also have an excretion orfice.
My question is:
- What would force an animal to evolve in such a way? What would be the advantages and disadvantages?
Note: it can be assumed that the immobile parts protect themselves from enemies by means of a strong venom or hunters who stay in the nest for security purposes.