Biologically speaking, is it true that there are no parasites in Parasyte?


Watching the anime "Parasyte - the maxim" I can't really see any of the
organisms shown as real parasites, from a biological/ecological viewpoint.

Can any of the different kinds of alien parasytes shown be classified as a
bona fide parasite?




I will use "parasite" (lower case, with an "i") to refer to the ecological
relationship, and "Parasyte" (upper case, with an "y") to refer to the manga
creatures.

* * *

From Wikipedia on [parasitism](http://en.wikipedia.org/wiki/Parasitism):

> Parasitism is a non-mutual symbiotic relationship between species, where one
> species, the parasite, benefits at the expense of the other, the host. (...)
> Unlike predators, parasites typically do not kill their host (...)

Then, on [decapitation](http://en.wikipedia.org/wiki/Decapitation):

> This form of injury invariably results in death (...)

* * *

So, on the three kinds of Parasytes:

  * The ones that "eat" the brain and take over the head, they already killed their hosts upon infection. So they **are not parasites** because they first **kill the host** , then inhabit the corpse. **Parasitism** is a kind of **symbiosis** , meaning that **both** organisms must be **alive**.

From [Livescience](http://www.livescience.com/42301-brain-death-body-
alive.html):

> A person is considered brain-dead when he or she no longer has any
> neurological activity in the brain or brain stem — meaning no electrical
> impulses are being sent between brain cells.

The head of those bodies is the Parasyte, the original human head long gone,
consumed by the Parasyte larvae. So there is no ecological relationship
between living organisms. The Parasyte simply took over the corpse of the
human they killed. Such is the case when a Parasyte changes bodies too, like
when

> Shinichi's mom is beheaded by the car crash Parasyte, because it needed a
> female body to inhabit.

We can then infer that these head-Parasytes are not parasites. The
relationship between them is [called
Metabiosis](http://en.wikipedia.org/wiki/Commensalism#Metabiosis).

  * The co-inhabiting Parasytes, like Migi and Joe, they are really either [mutualist symbiotes](http://en.wikipedia.org/wiki/Mutualism_%28biology%29) because the Parasyte provides his host with augmented abilities and protection from a predator (other Parasytes), and even if we think of a co-inhabiting Parasyte that stays dormant on his host, it would still be a case of [phoresis or inquilinism commensalism](http://en.wikipedia.org/wiki/Commensalism#Types). 

The human in the case of a commensalist symbiote would not be harmed or
hindered, because the Parasyte emulates the body part it "ate" and the
commensalist Parasytes are not too eager to kill their host since their
primary drive is survival, and as Migi states, without eating the brain they
do not know how to control a whole human body.

  * The colony Parasytes, like

> Miki and Gotou

are a colony of same-species organisms mimicking a human body. They are also
not parasites.

* * *

From the bullet points above, we can say that none of the Parasytes shown in
the manga or the anime (so far) are not really parasites.

