Possum, Oh Possum!

The possum has been back. And this time, I've got a better picture.

Sort of a big rat with bad hair. And long toes.

I've been confused about the name; is it possum, or opossum?  And is that the same as the Mexican tlacuache?

I Googled it, and now the confusion has doubled.

The American possums are actually called opossums, scientific name, Didelphimorphia. But for some reason, they are more commonly referred to as possums. ... Australian possums are (scientific name) Phalangeridae. Both are marsupials, but that’s about it. Other than that, they are not really related at all.(From BobInOz)

Here's Wikipedia on the American possums:

The opossums, also known by their scientific name Didelphimorphia ..., make up the largest order of marsupials in the Western Hemisphere, including 103 or more species in 19 genera. Of South American ancestry, they entered North America following the connection of the two continents.
...
The word "opossum" is borrowed from the Virginia Algonquian (Powhatan) language ... from the Proto-Algonquian word meaning "white dog" or "white beast/animal".
They are also commonly called possums, particularly in the Southern United States and Midwest. However, the term "possum" was borrowed into use to describe distantly related Australian marsupials (specifically those of the suborder Phalangeriformes) when Australia became known to Europeans.

They originated in South America, from where one species spread into the American Southeast, and then west and north to here. And in each country in Latin America, they go by a different name: "tlacuache" (from an Azetc word) in Mexico, which is the name I knew, and ...

en El Salvador como tacuazines ... en Ecuador como guanchacas, en Honduras como guasalos, en el Perú como mucas o canchalucos, en Bolivia como carachupas, en Colombia como faras, chuchas, runchos o raposas, en Venezuela como rabipelados ... (From Wikipedia in Spanish)

And the Latin name, Didelphimorphia, means "double womb", referring to the split reproductive system; baby possums are born very early in their development, and crawl up the mother's belly to a pouch where they attach themselves to a teat and grow until they're ready to face the world. They are marsupials, like the better-known kangaroo.

Looking up names, I learned that some of the things I "knew" about possums were wrong.

• "Possum" has been used in the phrase, "playing possum," referring to the habit of a threatened oppossum of keeling over and pretending to be dead. Except that they don't, really, all that often; only about 10% of possums play dead.


• They are also supposed to have prehensile tails, but this only shows up in the young; an adult is too heavy for his own tail.

UPDATE: Christopher Taylor adds, in the comments,

The "double womb" is actually a bit more literal than that. Unlike the situation in humans, where the Fallopian tubes lead from the ovaries on each side to a common central uterus, marsupials have an entirely separate uterus for each ovary, with a separate vagina for each (though only a single cervix, so I think there would still be only a single visible opening externally). I believe many male marsupials have a divided head to the penis, so that they are able to fertilise both sides of the female's reproductive system at once. Even though this feature is (I think) common to all marsupials, I suspect that Didelphis was the animal that got tagged with it because, of course, the American opossum was discovered by Europeans long before the Australian forms.

Two uteri, and a pouch, to boot! And then the mother carries her babies on her back for weeks after they're out of the pouch. The burden of motherhood is a heavy one for an opossum!