I don't understand how the transmissible venereal tumor isn't considered a species of its own (this will be quick because I have to go to sleep)
These hellish monstrosities basically meet all the criteria to be classified as such, and I stand by that.
1) Out of the roughly 20,000 genes a dog has, 10,000 show non-synonymous (functionally different) variations, and 646 have been lost; in other words, based solely on what is missing, they differ more from a dog than a chimpanzee does from a human.
2) As unicellular organisms, their morphology is completely different.
3) And as obligate parasites, their ecological niche is also completely different—in fact, they have evolved specifically for that role.
4) And, obviously, they are reproductively isolated.
As for potential objections:
1) Being a parasite is no reason to claim they lack sufficient independence or their own life cycle; \*Henneguya zschokkei\* cannot even breathe on its own.
2) The biological species concept is nonsense in cases like this; it cannot be applied to anything that reproduces asexually—which accounts for more than 90% of the species on Earth.
Anyway...
What do you think?